1 
ﺍﻟﻌﺭﺒﻴﺔ ﺍﻟﺨﻠﻴﺞ ﻟﺩﻭل ﺍﻟﺘﻌﺎﻭﻥ ﻤﺠﻠﺱ ﻟﺩﻭل ﺍﻟﺘﻘﻴﻴﺱ  ﻫﻴﺌﺔ 
GCC STANDARDIZATION ORGANIZATION (GSO) 
 
 
 
 
 
  ﻨﻬﺎﺌﻲ:  ﻤﺸﺭﻭﻉ 
 
  
 
GSO2/1/FDS/…: 2009 
 
 
 
 
 
  
   
 
 
ﺇﻋﺩﺍﺩ 
  ﻭﺍﻹﻁﺎﺭﺍﺕ  ﺍﻟﻤﺭﻜﺒﺎﺕ  ﻤﻭﺍﺼﻔﺎﺕ  ﻟﻘﻁﺎﻉ ﺍﻟﺨﻠﻴﺠﻴﺔ  ﺍﻟﻔﺭﻋﻴﺔ ﺍﻟﻔﻨﻴﺔ ﺍﻟﻠﺠﻨﺔ 
 
 
 
 
    ﻗﻴﺎﺴﻴﺔ ﻟﻤﻭﺍﺼﻔﺔ  ﻤﺸﺭﻭﻉ  ﺍﻟﻭﺜﻴﻘﺔ ﻫﺫﻩ            ﻓﺈﻨﻬـﺎ ﻟﺫﻟﻙ ﺒﺸﺄﻨﻬﺎ، ﻭﺍﻟﻤﻠﺤﻭﻅﺎﺕ  ﺍﻟﺭﺃﻱ ﻹﺒﺩﺍﺀ ﺘﻭﺯﻴﻌﻬﺎ  ﺘﻡ ﺨﻠﻴﺠﻴﺔ 
               ﻤﺠﻠﺱ ﻤﻥ ﺍﻋﺘﻤﺎﺩﻫﺎ  ﺒﻌﺩ ﺇﻻ ﺨﻠﻴﺠﻴﺔ ﻗﻴﺎﺴﻴﺔ ﻜﻤﻭﺍﺼﻔﺔ  ﺇﻟﻴﻬﺎ ﺍﻟﺭﺠﻭﻉ  ﻴﺠﻭﺯ ﻭﻻ ﻭﺍﻟﺘﺒﺩﻴل،  ﻟﻠﺘﻐﻴﻴﺭ ﻋﺭﻀﺔ
ﺍﻟﻬﻴﺌﺔ ﺇﺩﺍﺭﺓ.  ﺍﻟﺘﻲ ﺒﺎﻟﺴﻴﺎﺭﺍﺕ  ﺍﻟﺨﺎﺼﺔ  ﻟﻠﻤﻠﺤﻘﺎﺕ  ﺍﻟﺘﺭﻜﻴﺏ  ﻭﻁﺭﻴﻘﺔ  ﻤﺘﻁﻠﺒﺎﺕ -  ﺍﻟﺴﻴﺎﺭﺍﺕ
 ﺍﻟﻤﻀﻐﻭﻁ  ﺍﻟﻁﺒﻴﻌﻲ  ﺒﺎﻟﻐﺎﺯ ﺘﻌﻤل 
Motor Vehicles – Requirements & Installation of Components 
in Motor Vehicles using Compressed Natural Gas (CNG)  ﺘﻘﺩﻴﻡ  
ﺍﻷ ﻋﻀﻭﻴﺘﻬﺎ  ﻓﻲ ﺘﻀﻡ ﺇﻗﻠﻴﻤﻴﺔ ﻫﻴﺌﺔ ﺍﻟﻌﺭﺒﻴﺔ ﺍﻟﺨﻠﻴﺞ ﻟﺩﻭل ﺍﻟﺘﻌﺎﻭﻥ ﻤﺠﻠﺱ ﻟﺩﻭل ﺍﻟﺘﻘﻴﻴﺱ ﻫﻴﺌﺔ  ﺍﻟﻭﻁﻨﻴﺔ ﺠﻬﺯﺓ
 ﺍﻟﺨﻠﻴﺠﻴﺔ  ﺍﻟﻘﻴﺎﺴﻴﺔ ﺍﻟﻤﻭﺍﺼﻔﺎﺕ  ﺇﻋﺩﺍﺩ ﺍﻟﻬﻴﺌﺔ ﻤﻬﺎﻡ ﻭﻤﻥ ، ﺍﻟﻌﺭﺒﻴﺔ ﺍﻟﺨﻠﻴﺞ ﺩﻭل ﻓﻲ ﻭﺍﻟﻤﻘﺎﻴﻴﺱ  ﻟﻠﻤﻭﺍﺼﻔﺎﺕ
 ﻤﺘﺨﺼﺼﺔ  ﻓﻨﻴﺔ ﻟﺠﺎﻥ ﺒﻭﺍﺴﻁﺔ  . 
 
ﺭﻗﻡ ﺍﻟﻔﻨﻴﺔ ﺍﻟﻠﺠﻨﺔ ﻋﻤل ﺒﺭﻨﺎﻤﺞ ﻀﻤﻥ ﺍﻟﻌﺭﺒﻴﺔ ﺍﻟﺨﻠﻴﺞ ﻟﺩﻭل ﺍﻟﺘﻌﺎﻭﻥ ﻤﺠﻠﺱ ﻟﺩﻭل ﺍﻟﺘﻘﻴﻴﺱ ﻫﻴﺌﺔ ﻗﺎﻤﺕ ﻭﻗﺩ2-1 
 "  ﺍﻟﺨﻠﻴﺠﻴﺔ  ﺍﻟﻔﻨﻴﺔ ﻭﺍﻹﻁﺎﺭﺍﺕﺍﻟﻠﺠﻨﺔ  ﺍﻟﻤﺭﻜﺒﺎﺕ  ﻤﻭﺍﺼﻔﺎﺕ  ﻟﻘﻁﺎﻉ ﺍﻟﻔﺭﻋﻴﺔ "   ﺭﻗﻡﺒﺈﻋﺩﺍﺩ  ﺍﻟﻤﻭﺍﺼﻔﺔ "   
2009 …… /FDS/1/2 GSO "  ﺍﻟﺴﻴﺎﺭﺍﺕ - ﺍﻟﺘﻲ ﺒﺎﻟﺴﻴﺎﺭﺍﺕ  ﺍﻟﺨﺎﺼﺔ ﻟﻠﻤﻠﺤﻘﺎﺕ  ﺍﻟﺘﺭﻜﻴﺏ  ﻭﻁﺭﻴﻘﺔ ﻤﺘﻁﻠﺒﺎﺕ  
ﺍﻟﻤﻀﻐﻭﻁﺔ  ﺍﻟﻁﺒﻴﻌﻴﺔ  ﺒﺎﻟﻐﺎﺯﺍﺕ  ﺘﻌﻤل "   ﺒﺈﻋﺩﺍﺩ  ﻗﺒل ﻤﻥ ﺍﻟﺨﻠﻴﺠﻴﺔ  ﺍﻟﻘﻴﺎﺴﻴﺔ ﺍﻟﻤﻭﺍﺼﻔﺔ  ﻫﺫﻩ ﺍﻟﺒﺤﺭﻴﻥ  ﻤﻤﻠﻜﺔ  ﻭﻗﺩ 
ﺇﻋﺩ ﺘﻡ  ﺫﺍﺕ ﺍﻟﻤﺭﺠﻌﻴﺔ  ﻭﺍﻟﻤﺅﻟﻔﺎﺕ  ﻭﺍﻟﺩﻭﻟﻴﺔ  ﻭﺍﻷﺠﻨﺒﻴﺔ  ﺍﻟﻌﺭﺒﻴﺔ ﺍﻟﻘﻴﺎﺴﻴﺔ ﺍﻟﻤﻭﺍﺼﻔﺎﺕ  ﺍﺴﺘﻌﺭﺍﺽ  ﺒﻌﺩ ﺍﻟﻤﺸﺭﻭﻉ  ﺍﺩ
ﺍﻟﺼﻠﺔ  .
    
 ﺍﻟﻤﻭﺍﺼﻔﺔ  ﻫﺫﻩ ﺍﻋﺘﻤﺩﺕ  ﻭﻗﺩ  ﺨﻠﻴﺠﻴﺔ ﻓﻨﻴﺔ ﻜﻼﺌﺤﺔ    ﺭﻗﻡ ﺍﻟﻬﻴﺌﺔ ﺇﺩﺍﺭﺓ ﻤﺠﻠﺱ ﺍﺠﺘﻤﺎﻉ ﻓﻲ              
       )          ( ﺒﺘﺎﺭﻴﺦ ﻋﻘﺩ ﺍﻟﺫﻱ ،  /      /       ، ﻫـ          ﺍﻟﻤﻭﺍﻓﻕ/      /       ﻡ  . 
 
Foreword 
 
Standardization Organization for GCC (G SO) is a regional Organization which 
consists of the National Standards Bodi es of GCC member States. One of GSO 
main functions is to issu e Gulf Standards /Technical regulation through specialized 
technical committees (TCs). 
 
GSO through the technical pr ogram of committee TC No . 2-1 "  The Gulf technical 
Subcommittee for vehicles and tyres standard s " has prepared this Standard .  The 
Draft Standard has been prepared by Kingdom Of Bahrain .  
 
 The draft Standard has been prepared based on relevant ADM O, International and 
National foreign Standa rds and references. 
 
This standard has b een approved as Gulf  Standard by GSO Board of Directors in its 
meeting No..../....  …….held on    /    /   /  H ,  /    /   G GSO STANDARD                                                                     GSO  /    
 
 
 
Motor Vehicles – Requirements & Installation of Components in 
Motor Vehicles using Compressed Natural Gas (CNG)  
 
  
CONTENTS 
 REGULATION Page 
 
1. Scope....................................................................................................................... ..............  6 
 2.  Complementary  References  ……………………………………………………………… 6  3. Definition and classification of components ........................................................................  6  PART I  4. Specifications regarding CNG components........................................................................  13   PART II  5. Definitions ................................................................................................................. .........  15 
 6. Requirements for the installation of specific 
components for the use of compressed natural gas in the propulsion system of a vehicle .................................................................................  15 
  ANNEXES  Annex 1A
 - Essential characteristics of the CNG component 
 
Annex 1B  - Essential characteristics of the vehicle, engine and CNG-related system 
 Annex 2
 - Gas cylinders - High pressure cylinder for the on-board storage of natural gas 
as a fuel for automotive vehicles 
 
Annex 2 - Appendix A  - Test methods 
Annex 2 - Appendix B  - Report Forms 
Annex 2 - Appendix C  - Verification of stress ratios using strain gauges 
Annex 2 - Appendix D  - Fracture performance methods 
Annex 2 - Appendix E  - Instructions by the container manufacturer 
regarding handling, use and inspection of cylinders GSO STANDARD                                                                     GSO  /    
 
 
 4Annex 2 - Appendix F  - Environmental test 
 Annex 4A
 - Provisions regarding the approval of the automatic valve, non-return valve, the 
pressure relief valve, pressure relief device and the excess flow valve 
 Annex 4B
 - Provisions regarding the approval of flexible fuel lines or hoses 
 Annex 4C
 - Provisions regarding the approval of the CNG filter 
 Annex 4D
 - Provisions regarding the approval of the pressure regulator 
 Annex 4E
 - Provisions regarding the approval of the pressure and temperature sensors 
 Annex 4F
 - Provisions regarding the approval of the filling unit 
 Annex 4G
 - Provisions regarding the approval of ga s flow adjuster and gas/air mixer or 
injector  Annex 4H
 - Provisions regarding the approval of the electronic control unit 
 Annex 3
 - Test procedures 
 Annex 3A
 - Overpressure test (Strength test) 
 Annex 3B
 - External leakage test 
 Annex 3C
 - Internal leakage test 
 Annex 3D
 - CNG compatibility test 
 Annex 3E
 - Corrosion resistance test 
 Annex 3F
 - Resistance to dry heat 
 Annex 3G
 - Ozone ageing 
 Annex 3H
 - Temperature cycle test 
 Annex 3I
 - Pressure cycle test applicable only to cylinders (see Annex 2) 
 Annex 3J
 - (Not allocated) 
 Annex 3K
 - (Not allocated) 
 Annex 3L
 - Durability test (Continued operation) GSO STANDARD                                                                     GSO  /    
 
 
 5 Annex 3M
 - Burst/destructive test applicable only to cylinders (see Annex 2) 
 Annex 3N
 - Vibration resistance test 
 Annex 3O
 - Operating temperatures 
 Annex 4
 - Provisions regarding CNG identification mark for public service vehicles 
 Annex 5
 - Consolidated Resolution on the Construction of Vehicles (R.E.3), 
(document TRANS/WP.29/78/Rev.1/Amend.2, as last amended by Amend.4)).GSO STANDARD                                                                     GSO  /    
 
 
 61. SCOPE 
 
 This Regulation applies to:  1.1. Part I. Specific components for passe nger & multipurpose vehicles of    
category M and N
1  using compressed natural gas (CNG) in their 
propulsion system; 
 1.2. Part II. Vehicles of category M and N  with regard to the installation of 
specific components, for the use of  compressed natural gas (CNG) for 
propulsion, of an approved type. 
 
2.                    COMPLEMENTARY REFERENCES 
 
2.1 GSO 48 / 1984 “ Motor Vehicles Conformity Certificate” 
  
2.2 GSO 591 / 1995 “ Road Vehicles – Types, Terms & Definitions.”  
 
 
3. DEFINITION AND CLASSIFICATION OF COMPONENTS 
 
CNG components for use in vehicles shall be classified with regard to the working 
pressure and function, according to figure 1-1.  Class 0 High pressure parts including t ubes and fittings containing CNG at a 
pressure higher than 3 MPa and up to 26 MPa. 
 Class 1 Medium pressure parts includi ng tubes and fittings containing CNG at 
a pressure higher than 450 kPa and up to 3,000 kPa (3 MPa). 
 Class 2 Low pressure parts including t ubes and fittings containing CNG at a 
pressure higher than 20 kPa and up to 450 kPa. 
 
Class 3 Medium pressure parts as safety  valves or protected by safety valve 
including tubes and fittings containi ng CNG at a pressure higher than 
450 kPa and up to 3,000 kPa (3 MPa). 
 
Class 4 Parts in contact with gas subject to the pressure lower than 20 kPa.  A component can consist of se veral parts, each part classified in its own class with 
regard to maximum working pressure and function. 
 
                    
 
1 - F or the purpose of this regulation, refer to the definition of M & N category mentioned in Annex 5 
(Consolidated Resolution on the Construction of Vehicles (R.E.3), (document 
TRANS/WP.29/78/Rev.1/Amend.2, as  last amended by Amend.4)). GSO STANDARD                                                                     GSO  /    
 
 
 73.1. "Pressure " means relative pressure versus at mospheric pressure, unless otherwise 
stated. 
 3.1.1. "Service pressure
" means the settled pressure at a uniform gas temperature of 15 
°C. 
 3.1.2. "Test pressure
" means the pressure to which a component is taken during 
acceptance testing. 
 3.1.3. "Working  pressure
" means the maximum pressure to which a component is 
designed to be subjected to and which is the basis for determining the strength of 
the component under consideration. 
 3.1.4. "Operating temperatures
" means maximum values of the temperature ranges, 
indicated in Annex 3O, at which safe and good functioning of the specific component is ensured and for which it has been designed and approved. 
 3.2. "Specific component
" means: 
 
(a) container (or cylinder), (b) accessories fitted to the cylinder  (c) pressure regulator,  (d) automatic valve, (e) manual valve, 
(f) gas supply device, 
(g) gas flow adjuster, (h) flexible fuel line, (i) rigid fuel line, (j) filling unit or receptacle, (k) non-return valve or non-return valve, (l) pressure relief valve (discharge valve), (m) pressure relief device (temperature triggered), (n) filter, (o) pressure or temperature sensor / indicator, (p)  excess flow valve, (q)  service valve, (r) electronic control unit, (s) gas-tight housing, (t) fitting, (u) ventilation hose. 
 3.2.1. Many of the components mentioned above can  be combined or fitted together as a 
"multi-functional component". 
  GSO STANDARD                                                                     GSO  /    
 
 
 8
 GSO STANDARD                                                                     GSO  /    
 
 
 9Fig. 1-2  
 
TESTS  APPLICABLE  TO  SPECIFIC  CLASSES  OF  COMPONENTS 
(EXCLUDING CYLINDERS) 
 
 
Performance 
Test  
Over-
pressure 
Strength Test  
Leakage Test 
(external)  
Leakage 
Test 
(internal)  
Continued 
Operation 
Durability 
Test  
Corrosion 
Resistance 
  
Ozone 
Ageing  
CNG 
Compatibility  
Vibration 
Resistance  
Dry - Heat 
Resistance 
 
  
Annex 3A  
Annex 3B  
Annex 3C 
Annex 3L  
Annex 3E  
Annex 
3G  
Annex 3D  
Annex 3N  
Annex 3F 
 
Class 0  
X  
X  
A  
A  
X  
X  
X  
X  
X 
 
Class 1  
X  
X  
A  
A  
X  
X  
X  
X  
X 
 
Class 2  
X  
X  
A  
A  
X  
A  
X  
X  
A 
 
Class 3  
X  
X  
A  
A  
X  
X  
X  
X  
X 
 
Class 4  
O  
O  
O  
O  
X  
A  
X  
O  
A 
 
X   = Applicable O   = Not applicable A   = As applicable  3.3. "Container
" (or cylinder) means any vessel used  for the storage of compressed 
natural gas; 
 3.3.1. A container can be:  
CNG-1 metal;  
CNG-2 metal liner reinforced with resin impregnated continuous filament (hoop 
wrapped);  CNG-3 metal liner reinforced with resin impregnated continuous filament (fully 
wrapped);  CNG-4 resin impregnated continuous f ilament with a non-metallic liner (all 
composite). 
 3.4. "Type of container
" means containers which do not differ in respect of the 
dimensional and material characteristics as specified in Annex 2. 
 
3.5. "Accessories fitted to the container " means the following components (but not 
limited to them), either separate or combined, when fitted to the container: GSO STANDARD                                                                     GSO  /    
 
 
 10 3.5.1. Manual valve;  3.5.2. Pressure sensor/indicator;  
3.5.3. Pressure relief valve (discharge valve);  3.5.4. Pressure relief device (temperature triggered);  3.5.5. Automatic cylinder valve;  3.5.6. Excess flow valve;  3.5.7. Gas-tight housing.  3.6. "Valve
" means a device by which the flow of a fluid may be controlled. 
 
3.7. "Automatic valve " mans a valve which is not operated manually. 
 3.8. "Automatic cylinder valve
" means an automatic valve rigidly fixed to the cylinder 
which controls the flow of gas to the fuel system.  The automatic cylinder valve is also called remote-controlled service valve. 
 3.9. "Non-return valve
" means an automatic valve whic h allows gas to flow in only 
one direction. 
 3.10. "Excess flow valve
" (excess flow limiting device) means a device which 
automatically shuts off, or limits, the gas flow when the flow exceeds a set design value. 
 3.11. "Manual valve
" means a manual valve rigidly fixed to the cylinder. 
 3.12. "Pressure relief valve (discharge valve)
" means a device which prevents a pre-
determined upstream pressure being exceeded. 
 3.13. "Service valve
" means an isolation valve which is closed only when servicing the 
vehicle. 
 3.14. "Filter
" means a protective screen which re moves foreign debris from the gas 
stream. 
 3.15. "Fitting
" means a connector used in a piping, tubing, or hose system. 
3.16.  Fuel lines  
 3.16.1. "Flexible fuel lines
" mean a flexible tubing or hose through which natural gas GSO STANDARD                                                                     GSO  /    
 
 
 11flow. 
 3.16.2. "Rigid fuel lines
" mean a tubing which has not b een designed to flex in normal 
operation and through which natural gas flows. 
 3.17. "Gas supply device
" means a device for introducing gaseous fuel into the engine 
intake manifold (carburetor or injector). 
 3.17.1. "Gas/air mixer
" means a device for mixing the gaseous fuel and intake air for the 
engine. 
 3.17.2. "Gas injector
" means a device for introducing gaseous fuel into the engine or 
associated intake system. 
 3.18. "Gas flow adjuster
" means a gas flow restricting de vice, installed downstream of a 
pressure regulator, controlling gas flow to the engine. 
 3.19. "Gas-tight housing
" means a device which vents gas leakage to outside the vehicle 
including the gas ventilation hose. 
 3.20. "Pressure indicator
" means a pressurized device whic h indicates the gas pressure. 
 3.21. "Pressure regulator
" means a device used to control the delivery pressure of 
gaseous fuel to the engine. 
 3.22. "Pressure relief device (temperature triggered)
" means a one time use device 
triggered by excessive temperature and/or pressure which vents gas to protect the 
cylinder from rupture. 
 3.23. "Filling unit or receptacle
" means a device fitted in the vehicle external or internal 
(engine compartment) used to fill the container in the filling station. 
 3.24. "Electronic control unit (CNG - fuelling)
" means a device which controls the gas 
demand of the engine, and other engine pa rameters, and cuts off automatically the 
automatic valve, required by safety reason. 
 3.25. "Type of components
" as mentioned in paragraphs 3.6. to 3.23. above means 
components which do not differ in such e ssential respect as materials, working 
pressure and operating temperatures. 
 3.26. "Type of electronic control unit
" as mentioned in paragraph 3.24. means 
components which do not differ in such e ssential respect as the basic software 
principles excluding minor changes. GSO STANDARD                                                                     GSO  /    
 
 
 12PART I 
 
APPROVAL OF SPECIFIC COMPONENTS OF MOTOR VEHICLES USING 
COMPRESSED NATURAL GAS (CNG) IN THEIR PROPULSION SYSTEM 
  
4. SPECIFICATIONS REGARDING CNG COMPONENTS 
 
4.1. General provisions 
 
4.1.1. The specific components of vehicles us ing CNG in their propulsion system shall 
function in a correct and safe way as specified in this Regulation. 
 The materials of the components which are in contact with CNG shall be compatible with it (see Annex 3D).  Those parts of component whose correct and safe functioning is liable to be 
influenced by CNG, high pressure or vibr ations has to be submitted to relevant 
test procedures described in the annexes of this Regulation.  In particular the 
provisions of paragraphs 4.2. to 4.11. are to be fulfilled.  The specific components of vehicles usi ng CNG in their propulsion system shall 
comply with relevant electromagnetic compatibility (EMC) requirements according to Regulation No. 10, 02 series of amendments, or equivalent. 
 
4.2. Provisions regarding containers 
 
4.2.1. The CNG containers shall be type appr oved pursuant to the provisions laid down 
in Annex 2 to this Regulation. 
 
4.3. Provisions regarding components fitted to the container 
 
4.3.1. The container shall be equipped at l east with the following components, which 
may be either separate or combined: 
 4.3.1.1. manual valve,  4.3.1.2. automatic cylinder valve,  4.3.1.3. pressure relief device,  4.3.1.4. excess flow limiting device.  4.3.2. The container may be equipped with a gas-tight housing, if necessary.  GSO STANDARD                                                                     GSO  /    
 
 
 134.3.3. The components mentioned in paragr aphs 4.3.1. to 4.3.2. above shall be type 
approved pursuant to the provisions laid down in Annex 4 to this Regulation. 
 4.4.-4.11. Provisions regarding other components  
The components shown shall be type approved pursuant to the provisions laid 
down in the annexes which can be determined from the table below: 
 
Paragraph Component Annex 
4.4. Automatic valve 
Non-return valve or non-return valve 
Pressure relief valve Pressure relief device Excess flow valve 4A 
4.5. Flexible fuel line-hose 4B 
4.6. CNG filter 4C 
4.7. Pressure regulator 4D 
4.8. Pressure and temperature sensors 4E 
4.9. Filling unit or receptacle 4F 
4.10. Gas flow adjuster and gas/air mixer or 
injector 4G 
4.11. Electronic control unit 4H 
    GSO STANDARD                                                                     GSO  /    
 
 
 14PART II 
 
APPROVAL OF VEHICLES 
WITH REGARD TO THE INSTALLATION OF SPECIFIC COMPONENTS OF AN 
APPROVED TYPE FOR THE USE OF COMPRESSED NATURAL GAS (CNG) 
IN THEIR PROPULSION SYSTEM 
 
 
5. DEFINITIONS 
 
5.1. For the purposes of Part II of this Regulation: 
 5.1.1. "Approval of a vehicle
" means the approval of a vehi cle type of categories M and 
N with regard to its CNG system as an  original equipment for the use in its 
propulsion system; 
 
5.1.2. "Vehicle type " means vehicles fitted with specific components for the use of CNG 
in their propulsion system which do not differ with respect to the following conditions:  
 5.1.2.1. the manufacturer;  5.1.2.2. the type designation established by the manufacturer, 
 
5.1.2.3. the essential aspects of design and construction:  5.1.2.3.1. chassis/floor pan (obvious a nd fundamental differences); 
 5.1.2.3.2. the installation of the CNG equipmen t(obvious and fundamental differences). 
 5.1.3. "CNG system
" means an assembly of components (container(s) or cylinder(s), 
valves, flexible fuel lines, etc.) and conn ecting parts (rigid fuel lines, pipes fitting, 
etc.) fitted on motor vehicles using CNG in their propulsion system. 
 
 
6. REQUIREMENTS FOR THE INSTALLATION OF SPECIFIC 
COMPONENTS FOR THE USE OF  COMPRESSED NATURAL GAS IN 
THE PROPULSION SYSTEM OF A VEHICLE 
 
6.1. General 
 6.1.1. The CNG system of the vehicle shall function in a good and safe manner at the 
working pressure and operating temperatur es for which it has been designed and 
approved. 
 GSO STANDARD                                                                     GSO  /    
 
 
 156.1.2. All components of the system shall be type approved as individual parts pursuant 
to Part I of this Regulation. 
 6.1.3. The materials used in the system shall be suitable for use with CNG.  
6.1.4. All components of the system shall be fastened in a proper way.  6.1.5. The CNG system shall show no leaks, i.e. stay bubble-free for 3 minutes.  6.1.6. The CNG system shall be installed such that is has the best possible protection 
against damage, such as damage due to  moving vehicle components, collision, grit 
or due to the loading or unloading of the vehicle or the shifting of those loads. 
 6.1.7. No appliances shall be connected to the CNG system other than those strictly 
required for the proper operation of the engine of the motor vehicle. 
 6.1.7.1. Notwithstanding the provisions of paragr aph 6.1.7., vehicles may be fitted with a 
heating system to heat the passenger comp artment and/or the load area which is 
connected to the CNG system. 
 6.1.7.2. The heating system referred to in paragraph 6.1.7.1. shall be permitted if, in the 
view of the Technical Services res ponsible for conducting type-approval, the 
heating system is adequately protected  and the required operation of the normal 
CNG system is not affected. 
 6.1.8. Identification of CNG-fuelled vehicles of categories M2 and M3 . 
 
6.1.8.1. Vehicles of categories M2 and M3 e quipped with a CNG system shall carry a 
plate as specified in Annex 4. 
 6.1.8.2. The plate shall be installed on the front  and rear of the vehicle of category M
2 or 
M3 and on the outside of the doors on the right-hand side. 
 
6.2. Further requirements  6.2.1. No component of the CNG system, incl uding any protective materials which form 
part of such components, shall project beyond the outline of the vehicle, with the 
exception of the filling unit if this does not project more than 10 mm beyond its 
point of attachment. 
 
6.2.2. No component of the CNG system shall be located within 100 mm of the exhaust 
or similar heat source, unless such com ponents are adequately shielded against 
heat. 
 6.3. The CNG system GSO STANDARD                                                                     GSO  /    
 
 
 16 6.3.1. A CNG system shall contain at least the following components:
 
 17.3.1.1. Container(s) or cylinder(s);  6.3.1.2. Pressure indicator or fuel level indicator;  6.3.1.3. Pressure relief device (temperature triggered); 
 
6.3.1.4. Automatic cylinder valve;  6.3.1.5. Manual valve;  6.3.1.6. Pressure regulator;  6.3.1.7. Gas flow adjuster;  6.3.1.8. Excess flow limiting device;  6.3.1.9. Gas supply device;  6.3.1.10. Filling unit or receptacle;  6.3.1.11. Flexible fuel line;  6.3.1.12. Rigid fuel line;  6.3.1.13. Electronic control unit;  6.3.1.14. Fittings;  6.3.1.15. Gas-tight housing for those components installe d inside the luggage and passenger 
compartment.  If the gas-tight housing will be destroyed in case of fire, the 
pressure relief device may be covered by the gas-tight housing. 
 6.3.2. The CNG system may also include the following components:
 
 
6.3.2.1. Non-return valve or non-return valve;  6.3.2.2. Pressure relief valve;  6.3.2.3. CNG filter; 
 
6.3.2.4. Pressure and/or temperature sensor;  GSO STANDARD                                                                     GSO  /    
 
 
 176.3.2.5.  Fuel selection system and electrical system.  6.3.3. An additional automatic valve may be combined with the pressure regulator.  6.4. Installation of the container 
 6.4.1. The container shall be permanently inst alled in the vehicle and shall not be 
installed in the engine compartment. 
 6.4.2. The container shall be installed such that  there is no metal to metal contact, with 
the exception of the fixing points of the container(s). 
 6.4.3. When the vehicle is ready for use the fuel container shall not be less than 200 mm 
above the road surface. 
 6.4.3.1. The provisions of paragraph 6.4.3. shall not apply if the container is adequately 
protected, at the front and th e sides and no part of the container is located lower 
than this protective structure. 
 6.4.4. The fuel container(s) or cylinder(s) mu st be mounted and fixed so that the 
following accelerations can be absorbed (without damage occurring) when the containers are full: 
 
Vehicles of categories M
1 and N 1: 
(a) 20 g in the direction of travel 
(b) 8 g horizontally perpendicular to the direction of travel  Vehicles of categories M
2 and N 2: 
(a) 10 g in the direction of travel (b) 5 g horizontally perpendicular to the direction of travel  Vehicles of categories M
3 and N 3: 
(a) 6.6 g in the direction of travel (b) 5 g horizontally perpendicular to the direction of travel  A calculation method can be used instead of practical testing if its equivalence can be demonstrated by the applicant for approval to the satisfaction of the Technical Service. 
 
6.5. Accessories fitted to the container(s) or cylinder(s)  6.5.1. Automatic valve
 
 
6.5.1.1. An automatic cylinder valve shall be installed directly on each container.  GSO STANDARD                                                                     GSO  /    
 
 
 186.5.1.2. The automatic cylinder valve shall be operated such that the fuel supply is cut off 
when the engine is switched off, irresp ective of the position of the ignition switch, 
and shall remain closed while the engine in not running.  A delay of 2 seconds is 
permitted for diagnostic. 
 
6.5.2. Pressure relief device  
 
6.5.2.1. The pressure relief device (temperature triggered) shall be fitted to the fuel 
container(s) in such a manner that can disc harge into the gas-tight housing if that 
gas-tight housing fulfils the requirements of paragraph 6.5.5. 
 6.5.3. Excess flow valve on the container
 
 6.5.3.1. The excess flow limiting device shall be fitted in the fuel container(s) on the 
automatic cylinder valve. 
 6.5.4. Manual valve
 
 6.5.4.1. A manual valve is rigidly fixed to the cylinder which can be integrated into the 
automatic cylinder valve. 
 6.5.5. Gas-tight housing on the container(s)
 
 6.5.5.1. A gas-tight housing over the container(s) fittings, which fulfils the requirements 
of paragraphs 6.5.5.2. to 6.5.5.5. shall be fitte d to the fuel container, unless the 
container(s) is installed outside the vehicle. 
 6.5.5.2. The gas-tight housing shall be in open connection with the atmosphere, where 
necessary through a connecting hose and a lead-through which shall be resistant 
against CNG. 
 
6.5.5.3. The ventilation opening of the gas tight housing shall not discharge into a wheel 
arch, nor shall it be aimed at a heat source such as the exhaust. 
 6.5.5.4. Any connecting hose and lead-through in  the bottom of the bodywork of the 
motor vehicle for ventilation of the gas- tight housing shall have a minimum clear 
opening of 450 mm
2.  
 
6.5.5.5. The housing over the container(s) fittings and connecting hoses shall be gas-tight 
at a pressure of 10 kPa without any permanent deformations.  In these circumstances a leak not exceeding 100 cm
3 per hour may be accepted. 
 6.5.5.6. The connecting hose shall be secured by cl amps, or other means, to the gas-tight 
housing and the lead-through to ensure that a gas-tight joint is formed. 
 GSO STANDARD                                                                     GSO  /    
 
 
 196.5.5.7. The gas-tight housing shall contain all th e components installed into the luggage 
or passenger compartment. 
 6.6. Rigid and flexible fuel lines  
6.6.1.  Rigid fuel lines shall be made of seamle ss material:  either stainless steel or steel 
with corrosion-resistant coating. 
 6.6.2. The rigid fuel line may be replaced by a flex ible fuel line if used in Class 0, 1 or 2. 
 6.6.3. Flexible fuel line shall fulfil the requirement of Annex 4B to this Regulation.  6.6.4. Rigid fuel lines, shall be secured such that  they shall not be subjected to vibration 
of stresses. 
 6.6.5. Flexible fuel lines shall be secured su ch that they shall not be subjected to 
vibration or stresses. 
 6.6.6. At the fixing point, the fuel line, flexible or rigid, shall be fitted in such a way that 
there is no metal to metal contact. 
 6.6.7. Rigid and flexible fuel gas line shall not be located at jacking points.  6.6.8. At passages the fuel lines shall be fitted with protective material.   6.7. Fitting or gas connections between the components   
 6.7.1. Soldered joints and bite-type compression joints are not permitted.  6.7.2. Stainless steel tubes shall only be  joined by stainless steel fittings. 
 6.7.3. Distributing-blocks shall be made of corrosion-resistant material.  6.7.4. Rigid fuel lines shall be connected by a ppropriate joints, for example, two-part 
compression joints in steel tubes and joints with olives tapered on both sides. 
 6.7.5. The number of joints shall be limited to a minimum.  6.7.6. Any joints shall be made in locations where access is possible for inspection.  6.7.7. In a passenger compartment or enclosed luggage compartment th e fuel lines shall 
be no longer than reasonably required, and in any case shall be protected by a gas-
tight housing. 
 6.7.7.1. The provisions of paragraph 6.7.7. shall not apply to vehicles of categories M2 or GSO STANDARD                                                                     GSO  /    
 
 
 20M3 where the fuel lines and connections are fitted with a sleeve which is resistant against CNG and which has an open connection to the atmosphere. 
 6.8. Automatic valve  
6.8.1. An additional automatic valve may be insta lled in the fuel line as close as possible 
to the pressure regulator. 
 6.9. Filling unit or receptacle  6.9.1. The filling unit shall be secured against ro tation and shall be protected against dirt 
and water. 
 6.9.2. When the CNG container is installed in  the passenger compartment or a enclosed 
(luggage) compartment the filling unit shall be  located at the outside of the vehicle 
or in engine compartment. 
6.9.3. For vehicles of classes M
1 and N 1 the filling unit (receptacl e) shall comply with 
the drawing specifications detailed in Figure 1 of Annex 4F. 1 / 
 
6.10. Fuel selection system and electrical installation  6.10.1. The electrical components of the CNG system shall be protected against 
overloads. 
 
6.10.2. Vehicles with more than one fuel system  shall have a fuel selection system to 
ensure that no more than one fuel at th e same time is supplied to the engine for 
more than 5 seconds.  "Dual-fuel
" vehicles, using diesel as the primary fuel for 
igniting the air/gas mixture, are allowed in cases where these engines and vehicles 
meet mandatory emission standards. 
 6.10.3. The electrical connections and compone nts in the gas-tight housing shall be 
constructed such that no sparks are generated. 
 GSO STANDARD                                                                     GSO  /    
 
 
 21Annex 1A  
 
ESSENTIAL CHARACTERISTICS OF THE CNG COMPONENT 
  1.2.4.5.1. System description:  1.2.4.5.2. Pressure regulator(s):  yes/no 1
/ 
 1.2.4.5.2.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.2.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.2.5. Drawings:......................................................................................................... ..........  
 
1.2.4.5.2.6. Number of main adjustment points ...........................................................................   1.2.4.5.2.7. Description of principle of adjustme nt through main adjustment points: .................  
 1.2.4.5.2.8. Number of idle adjustment points: ............................................................................   1.2.4.5.2.9. Description of principles of adjust ment through idle adjustment points:..................  
 1.2.4.5.2.10. Other adjustment possibilities: if so and which (description and drawings):  1.2.4.5.2.11. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.2.12. Material:........................................................................................................ .............  
 
1.2.4.5.2.13. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.3. Gas/air mixer: yes/no 1 / 
 1.2.4.5.3.1. Number: ........................................................................................................... ..........  
 1.2.4.5.3.2. Make(s):.......................................................................................................... ...........  
 1.2.4.5.3.3. Type(s):.......................................................................................................... ............  
 
1.2.4.5.3.4. Drawings:......................................................................................................... ..........  
1.2.4.5.3.5. Adjustment possibilities: ......................................................................................... ..  
 1.2.4.5.3.6. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.3.7. Material:......................................................................................................... ............  GSO STANDARD                                                                     GSO  /    
 
 
 22 
1.2.4.5.3.8. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.4. Gas flow adjuster: yes/no 1 / 
 1.2.4.5.4.1. Number: ........................................................................................................... ..........  
 1.2.4.5.4.2. Make(s):.......................................................................................................... ...........  
 1.2.4.5.4.3. Type(s):.......................................................................................................... ............  
 
1.2.4.5.4.4. Drawings:......................................................................................................... ..........  
 1.2.4.5.4.5. Adjustment possibilities (description)  1.2.4.5.4.6 Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.4.7. Material:......................................................................................................... ............  
 
1.2.4.5.4.8. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.5. Gas injector(s): yes/no 1 / 
 1.2.4.5.5.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.5.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.5.3. Identification:................................................................................................... ..........  
 
1.2.4.5.5.4. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.5.5. Drawings of installation: ......................................................................................... ..  
 1.2.4.5.5.6. Material:......................................................................................................... ............  
 
1.2.4.5.5.7. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.6. Electronic Control Unit (CNG-fuelling): yes/no 1 / 
 1.2.4.5.6.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.6.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.6.3. Adjustment possibilities: ......................................................................................... ..  
 GSO STANDARD                                                                     GSO  /    
 
 
 231.2.4.5.6.4. Basic software principles:........................................................................................ ..  
 
1.2.4.5.6.5. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.7. CNG container(s) or cylinder(s):  yes/no 1 / 
 1.2.4.5.7.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.7.2. Type(s) (include drawings): ......................................................................................   1.2.4.5.7.3. Capacity:......................................................................................................... ... litres 
 
1.2.4.5.7.4. Drawings of the installation of the container: ...........................................................   1.2.4.5.7.5. Dimensions: ....................................................................................................... ........  
 1.2.4.5.7.6. Material:......................................................................................................... ............  
 1.2.4.5.8. CNG container accessories  1.2.4.5.8.1. Pressure indicator:
  yes/no 1 / 
 
1.2.4.5.8.1.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.1.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.1.3. Operating principle: float/other 1
/ (include description or 
  drawings) ...................................................................................................................   1.2.4.5.8.1.4. Working pressure(s): 2
/ ......................................................................................MPa 
 1.2.4.5.8.1.5. Material:....................................................................................................... ..............  
 
1.2.4.5.3.1.6. Operating temperatures: 2
/ ................................................................................... °C 
1.2.4.5.8.2. Pressure relief valve (discharge valve):  yes/no 1 / 
 
1.2.4.5.8.2.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.2.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.2.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.2.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.2.5. Operating temperatures: 2
/ ................................................................................... °C GSO STANDARD                                                                     GSO  /    
 
 
 24 1.2.4.5.8.3. Automatic cylinder valve
 
 1.2.4.5.8.3.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.3.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.3.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.3.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.3.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.4. Excess flow valve : yes/no 1 / 
 1.2.4.5.8.4.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.4.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.4.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.4.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.4.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.5. Gas-tight housing:  yes/no 1 / 
 1.2.4.5.8.5.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.5.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.5.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.5.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.5.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.6. Manual valve:  yes/no 1 / 
 1.2.4.5.8.6.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.6.2. Type(s):........................................................................................................ ..............   
 1.2.4.5.8.6.3. Drawings:....................................................................................................... ............  
 GSO STANDARD                                                                     GSO  /    
 
 
 251.2.4.5.8.6.4. Working pressure(s) 2 /: ......................................................................................MPa 
 1.2.4.5.8.6.5. Material:....................................................................................................... ..............  
 
1.2.4.5.8.6.6. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.9. Pressure relief device (temperature triggered):  yes/no 1 / 
 1.2.4.5.9.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.9.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.9.3. Description and drawings:.........................................................................................  
 
1.2.4.5.9.4. Activation temperature: 2
/..................................................................................... °C 
 
1.2.4.5.9.5. Material:......................................................................................................... ............  
 
1.2.4.5.9.6. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.10. Filling unit or receptacle: yes/no 1 / 
 1.2.4.5.10.1. Make(s):......................................................................................................... ............  
 1.2.4.5.10.2. Type(s):......................................................................................................... .............  
 1.2.4.5.10.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.10.4. Description and drawings:........................................................................................ . 
 1.2.4.5.10.5. Material:........................................................................................................ .............  
 
1.2.4.5.10.6. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.11. Flexible fuel lines: yes/no 1 / 
 1.2.4.5.11.1. Make(s):......................................................................................................... ............  
 1.2.4.5.11.2. Type(s):......................................................................................................... .............  
 1.2.4.5.11.3. Description: ..................................................................................................... ..........  
 
1.2.4.5.11.4. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.11.5. Material:........................................................................................................ .............  GSO STANDARD                                                                     GSO  /    
 
 
 26 
1.2.4.5.11.6. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.12. Pressure and Temperature sensor(s):  yes/no 1 /  
 1.2.4.5.12.1. Make(s):......................................................................................................... ............  
 1.2.4.5.12.2. Type(s):......................................................................................................... .............  
 1.2.4.5.12.3. Description: ..................................................................................................... ..........  
 
1.2.4.5.12.4. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.12.5. Material:........................................................................................................ .............  
 
1.2.4.5.12.6. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.13. CNG filter(s):  yes/no 1 /  
 1.2.4.5.13.1. Make(s):......................................................................................................... ............  
 1.2.4.5.13.2. Type(s):......................................................................................................... .............  
 1.2.4.5.13.3. Description: ..................................................................................................... ..........  
 
1.2.4.5.13.4. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.13.5. Material:........................................................................................................ .............  
 
1.2.4.5.13.6. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.14. Non-return valve(s) or non-return valve(s): yes/no 1 / 
 1.2.4.5.14.1.  Make(s):........................................................................................................ .............  
 1.2.4.5.14.2.  Type(s):........................................................................................................ ..............  
 1.2.4.5.14.3.  Description: .................................................................................................... ...........  
 
1.2.4.5.14.4.  Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.14.5.  Material:....................................................................................................... ..............  
 
1.2.4.5.14.6. Operating temperatures: 2 / ................................................................................... °C 
 GSO STANDARD                                                                     GSO  /    
 
 
 271.2.4.5.15. Connection to CNG system for heating system: yes/no 1 /  
 1.2.4.5.15.1. Make(s):......................................................................................................... ............  
 1.2.4.5.15.2. Type(s):......................................................................................................... .............  
 1.2.4.5.15.3. Description and drawings of installation:..................................................................  
 
1.2.5. Cooling system: (liquid/air) 1
/ 
 
1.2.5.1.  System description/drawings with regard to the CNG system: 
 .............................................................................................................................. .....  
   
______________________ 
1
/ Strike out what does not apply. 
2/ Specify the tolerance. GSO STANDARD                                                                     GSO  /    
 
 
Annex 1B  
 
ESSENTIAL CHARACTERISTICS OF THE VEHICLE, 
ENGINE AND CNG-RELATED SYSTEM 
 0. DESCRIPTION OF THE VEHICLE(S)   
0.1. Make:..................................................................................................................... ....  
 0.2. Type(s):.................................................................................................................. ....  
 0.3.  Name and address of the manufacturer: ....................................................................   0.4. Engine type(s) and approval No.(Nos.):....................................................................   1. DESCRIPTION OF THE ENGINE(S)  1.1. Manufacturer: ............................................................................................................   1.1.1. Manufacturer's engine code(s) (as mark ed on the engine, or other means of 
identification): 
 1.2. Internal combustion engine  1.2.3. (Not allocated)  1.2.4.5.1. (Not allocated)  
1.2.4.5.2. Pressure regulator(s): 
 1.2.4.5.2.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.2.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.2.3. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.2.4. Material:......................................................................................................... ............  
 
1.2.4.5.2.5. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.3. Gas/air mixer:  yes/no 1 / 
 1.2.4.5.3.1. Number: ........................................................................................................... ..........  
 1.2.4.5.3.2. Make(s):.......................................................................................................... ...........  
 1.2.4.5.3.3. Type(s):.......................................................................................................... ............  
 GSO STANDARD                                                                     GSO  /    
 
 
 291.2.4.5.3.4. Working pressure(s): 2 / ....................................................................................... kPa 
 1.2.4.5.3.5. Material:......................................................................................................... ............  
 
1.2.4.5.3.6. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.4. Gas flow adjuster: yes/no 1 / 
 1.2.4.5.4.1. Number: ........................................................................................................... ..........  
 1.2.4.5.4.2. Make(s):.......................................................................................................... ...........  
 1.2.4.5.4.3. Type(s):.......................................................................................................... ............  
 
1.2.4.5.4.4. Working pressure(s): 2
/ ....................................................................................... kPa 
 
1.2.4.5.4.5. Material:......................................................................................................... ............  
 
1.2.4.5.4.6. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.5. Gas injector(s): yes/no 1 / 
 1.2.4.5.5.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.5.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.5.3. Working pressure(s): 2
/ ....................................................................................... kPa 
 1.2.4.5.5.4. Material:......................................................................................................... ............  
 
1.2.4.5.5.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.6. Electronic Control Unit CNG-fuelling:  yes/no 1 / 
 1.2.4.5.6.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.6.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.6.3. Basic software principles:........................................................................................ ..  
 
1.2.4.5.6.4. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.7. CNG container(s) or cylinder(s):  yes/no 1 / 
 1.2.4.5.7.1. Make(s):.......................................................................................................... ...........  GSO STANDARD                                                                     GSO  /    
 
 
 30 1.2.4.5.7.2. Type(s):.......................................................................................................... ............  
 1.2.4.5.7.3. Capacity:......................................................................................................... ... litres 
 
1.2.4.5.7.4. Approval number:.................................................................................................. ....  
 1.2.4.5.7.5. Dimensions: ....................................................................................................... ........  
 1.2.4.5.7.6. Material:......................................................................................................... ............  
 1.2.4.5.8. CNG container accessories:  1.2.4.5.8.1. Pressure indicator:
 
 
1.2.4.5.8.1.1. Make(s)......................................................................................................... .............  
 1.2.4.5.8.1.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.1.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.1.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.1.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.2. Pressure relief valve (discharge valve):   yes/no 1 / 
 1.2.4.5.8.2.1 Make(s):......................................................................................................... ............  
 1.2.4.5.8.2.2 Type(s):......................................................................................................... .............  
 1.2.4.5.8.2.3 Working pressure 2
/: ..........................................................................................MPa 
 1.2.4.5.8.2.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.2.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.3. Automatic valve(s):  
 1.2.4.5.8.3.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.3.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.3.3. Working pressure(s) 2
/: ......................................................................................MPa 
 GSO STANDARD                                                                     GSO  /    
 
 
 311.2.4.5.8.3.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.3.5. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.8.4. Excess flow valve : yes/no 1 / 
 1.2.4.5.8.4.1. Make(s):........................................................................................................ .............  
 1.2.4.5.8.4.2. Type(s):........................................................................................................ ..............  
 1.2.4.5.8.4.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.4.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.4.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.5. Gas-tight housing:   yes/no 1 / 
 1.2.4.5.8.5.1 Make(s):......................................................................................................... ............  
 1.2.4.5.8.5.2 Type(s):......................................................................................................... .............  
 1.2.4.5.8.5.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.5.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.5.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.8.6. Manual valve:  
 1.2.4.5.8.6.1 Make(s):......................................................................................................... ............  
 1.2.4.5.8.6.2 Type(s):......................................................................................................... .............  
 1.2.4.5.8.6.3 Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.8.6.4. Material:....................................................................................................... ..............  
 
1.2.4.5.8.6.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.9. Pressure relief device (temperature triggered):  yes/no 1 / 
 1.2.4.5.9.1. Make(s):.......................................................................................................... ...........  
 1.2.4.5.9.2. Type(s):.......................................................................................................... ............  GSO STANDARD                                                                     GSO  /    
 
 
 32 
1.2.4.5.9.3. Activation temperature: 2 /..................................................................................... °C 
 
1.2.4.5.9.4. Material:......................................................................................................... ............  
 
1.2.4.5.9.5. Operating temperatures: 2 / ................................................................................... °C 
 
1.2.4.5.10. Filling unit or receptacle:  yes/no 1 / 
 1.2.4.5.10.1. Make(s):......................................................................................................... ............  
 1.2.4.5.10.2. Type(s):......................................................................................................... .............  
 1.2.4.5.10.3. Working pressure(s) 2
/: ......................................................................................MPa 
 1.2.4.5.10.4. Material:........................................................................................................ .............  
 
1.2.4.5.10.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.11. Flexible fuel lines:  yes/no 1 / 
 1.2.4.5.11.1. Make(s):......................................................................................................... ............  
 1.2.4.5.11.2. Type(s):......................................................................................................... .............  
 1.2.4.5.11.3. Working pressure(s): 2
/ ....................................................................................... kPa 
 1.2.4.5.11.4. Material:........................................................................................................ .............  
 
1.2.4.5.11.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.12. Pressure and temperature sensor(s):  yes/no 1 /  
 1.2.4.5.12.1. Make(s):......................................................................................................... ............  
 1.2.4.5.12.2. Type(s):......................................................................................................... .............  
 1.2.4.5.12.3. Working pressure(s): 2
/ ....................................................................................... kPa 
 1.2.4.5.12.4. Material:........................................................................................................ .............  
 
1.2.4.5.12.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.13. CNG filter:  yes/no 1 /  
 GSO STANDARD                                                                     GSO  /    
 
 
 331.2.4.5.13.1. Make(s):......................................................................................................... ............  
 1.2.4.5.13.2. Type(s):......................................................................................................... .............  
 1.2.4.5.13.3. Working pressure(s): 2
/ ....................................................................................... kPa 
 1.2.4.5.13.4. Material:........................................................................................................ .............  
 
1.2.4.5.13.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.14. Non-return valve(s) or non-return valve(s): yes/no 1  
 1.2.4.5.14.1. Make(s):......................................................................................................... ............  
 1.2.4.5.14.2.  Type(s):........................................................................................................ ..............  
 1.2.4.5.14.3.  Working pressure(s): 2
/ ....................................................................................... kPa 
 1.2.4.5.14.4. Material:........................................................................................................ .............  
 
1.2.4.5.14.5. Operating temperatures: 2
/ ................................................................................... °C 
 
1.2.4.5.15. Connection to CNG system for heating system: yes/no 1 /  
 1.2.4.5.15.1. Make(s):......................................................................................................... ............  
 1.2.4.5.15.2. Type(s):......................................................................................................... .............  
 1.2.4.5.15.3. Description and drawings of installation:..................................................................  
 
1.2.4.5.16. Further documentation:............................................................................................. . 
 1.2.4.5.16.1. Description of the CNG system   1.2.4.5.16.2. System lay-out (electrical connections, vacuum connections compensation 
hoses, etc.): 
 1.2.4.5.16.3. Drawing of the symbol:  1.2.4.5.16.4. Adjustment data:................................................................................................. .......  
 1.2.4.5.16.5. Certificate of the vehicle on petrol, if already granted:  1.2.5. Cooling system: (liquid/air) 1
/ 
 GSO STANDARD                                                                     GSO  /    
 
 
 34     
______________________ 
1
/ Strike out what does not apply. 
2/ Specify the tolerance. 
 
   
 GSO STANDARD                                                                     GSO  /    
 
 
Annex 2  
 
GAS CYLINDERS HIGH PRESSURE CYL INDER FOR THE ON-BOARD STORAGE 
OF NATURAL GAS AS A FUEL FOR AUTOMOTIVE VEHICLES 
 1. SCOPE 
 
This annex sets out minimum requirements for light-weight refillable gas 
cylinders.  The cylinders are intended only for the onboard storage of high pressure compressed natural gas as a fuel  for automotive vehicles to which the 
cylinders are to be fixed.  Cylinders may be of any steel, aluminium or non-metallic material, design or method of manufacture suitable for the specified 
service conditions.  This annex also covers  stainless steel meta l liners of seamless 
or welded construction.  Cylinders covered by this annex are classified in Class 0, 
as described in paragraph 2. of this Regulation, and are:  CNG-1 Metal  CNG-2 Metal liner reinforced with resin impregnated continuous filament 
(hoop wrapped) 
 CNG-3 Metal liner reinforced with resin impregnated continuous filament 
(fully wrapped) 
 CNG-4 Resin impregnated continuous f ilament with a non- metallic liner (all 
composite) 
 Service conditions to which the cylinders will be subjected are detailed in paragraph 4. This annex is based upon a work ing pressure for natural gas as a fuel 
of 20 MPa settled at 15 °C with a maximum filling pressure of 26 MPa. Other 
working pressures can be accommodate d by adjusting the pressure by the 
appropriate factor (ratio). For example,  a 25 MPa working pressure system will 
require pressures to be multiplied by 1.25.  The service life of the cylinder shall be defined by the manufacturer and may vary 
with applications. Definition of servi ce life is based upon filling the cylinders 
1,000 times a year for a minimum of 15,000 fills. The maximum service life shall 
be 20 years.  For metal and metal-lined cylinders, the cylinder life is based upon the rate of 
fatigue crack growth. The ultrasonic inspec tion, or equivalent, of each cylinder or 
liner is required to ensure the absen ce of flaws which exceed the maximum 
allowable size. This approach permits the optimised design and manufacture of 
light weight cylinders for natural gas vehicle service.  For all-composite cylinders with non-me tallic non-load bearing liners the "safe 
life" is demonstrated by appropriate de sign methods, design qualification testing 
and manufacturing controls. GSO STANDARD                                                                     GSO  /    
 
 36 
2. REFERENCES 
 
The following standards contain provisions which, through reference in this text, constitute provisions of this annex. 
 
ASTM Standards 1
/ 
 
ASTM B117-90 Test method of Salt Spray (Fog) Testing,  ASTM B154-92 Mercurous Nitrate Test for Copper and Copper 
Alloys 
 
ASTM D522-92 Mandrel Bend Test of attached Organic Coatings; 
 ASTM D1308-87 Effect of Hous ehold Chemicals on Clear and 
Pigmented Organic Finishes; 
 ASTM D2344-84 Test Method for Apparent interlaminar Shear 
Strength of Parallel Fibre Composites by Short Beam Method; 
 ASTM D2794-92 Test Method for Resi stance of Organic Coatings to 
the Effects of Rapid Deformation (Impact); 
 ASTM D3170-87 Chipping Resistance of Coatings;  ASTM D3418-83 Test Method for Tran sition Temperatures Polymers 
by Thermal Analysis; 
 ASTM E647-93 Standard Test, Method for Measurement of Fatigue 
Crack Growth Rates; 
 ASTM E813-89 Test Method for J
IC, a Measure of Fracture 
Toughness; 
 
ASTM G53-93 Standard Practice for Operating Light and Water - 
Exposure Apparatus (Fluor escent UV-Condensation 
Type) for Exposure of non-metallic materials 
 
BSI Standards 2 / 
 
                     
1/ American Society for Testing and Materials. 
2/ British Standards Institution. GSO STANDARD                                                                     GSO  /    
 
 
 37BS 5045:  Part 1 (1982) Transportable Gas Containers - 
Specification for Seamless Steel Gas Containers Above 0.5 litre Water Capacity 
  
BS 7448-91 Fracture Mechanics T oughness Tests Part I - Method 
for Determination of K
IC, Critical COD and Critical 
J Values of BS PD 6493- 1991.Guidance an  Methods 
for Assessing the A Acceptability of Flaws in Fusion 
Welded Structures; Metallic Materials 
 EN 13322-2 2003 Transportable gas cylinders – Refillable welded steel 
gas cylinders - Design and construction – Part 2: 
Stainless steel 
 
EN ISO 5817 2003 Arc-welded joints in  steel; guidance on quality levels 
for imperfections 
 ISO Standards 3
/ 
 
ISO 148-1983 Steel - Charpy Impact Test (v-notch);  ISO 306-1987 Plastics - Thermoplastic Materials - Determination of 
Vicat Softening Temperature ; 
 
ISO 527 Pt 1-93 Plastics - Determination of Tensile Properties - 
Part I: General principles; 
 
ISO 642-79 Steel-Hardenability Test by End Quenching 
(Jominy Test); 
 ISO 2808-91 Paints and Varnishes - Determination of film 
Thickness; 
ISO 3628-78 Glass Reinforced Materials - Determination of 
Tensile Properties 
 ISO 4624-78 Plastics and Varnishes - Pull-off Test for adhesion;  ISO 6982-84 Metallic Materials - Tensile Testing,  ISO 6506-1981 Metallic Materials - Hardness test - Brinell Test;  ISO 6508-1986 Metallic Materials - Ha rdness Tests - Rockwell Test 
                    
 
3/ International Organization for Standardization. GSO STANDARD                                                                     GSO  /    
 
 38(Scales, ABCDEFGHK); 
 
ISO 7225 Precautionary Labels for Gas Cylinders,  ISO/DIS 7866-1992 Refillable Transportable Seamless Aluminium Alloy 
Cylinders for Worldwide Usage Design, Manufacture and Acceptance; 
 
ISO/DIS 12737 Metallic Materials - Determination of the Plane-
Strain Fracture Toughness; 
 ISO/IEC Guide 25-1990 General requirements for the Technical Competence 
of Testing Laboratories; 
 ISO/IEC Guide 48-1986 Guidelines for Third Party Assessment and 
Registration of Supplies Quality System; 
 ISO/DIS 9809 Transportable Seamle ss Steel Gas Cylinders Design, 
Construction and Testing - Part I: Quenched and Tempered Steel Cylinders with Tensile Strength < 1100 MPa; 
 NACE Standard 4
/ 
 
NACE TM0177-90 Laboratory Testing of  Metals for Resistance to 
Sulphide Stress Cracking in H 2S Environments. 
 
3. DEFINITIONS 
 
 For the purpose of this annex the following definitions shall apply:  3.1. (not allocated)  
3.2. auto-frettage
: A pressure application procedur e used in manufacturing composite 
cylinders with metal liners, which strains the liner past its limit of elasticity, 
sufficiently to cause permanent plastic deformation which results in the liner 
having compressive  stresses and the fibres  having tensile stresse s at zero internal 
pressure. 
 3.3. auto-frettage pressure
: The pressure within the over-wrapped cylinder at which 
the required distribution of stresses be tween the liner and the over-wrap is 
established. 
 
                     
4/ National Association of Corrosion Engineers. GSO STANDARD                                                                     GSO  /    
 
 
 393.4. batch - composite cylinders : A "batch" shall be a group of cylinders successively 
produced from qualified liners having the sa me size, design, specified materials of 
construction and process of manufacture. 
 3.5. batch - metal cylinders and liners
: A "batch" shall be a group of metal cylinders or 
liners successively produced having the sa me  nominal diameter, wall thickness, 
design, specified material of constructi on, process of manufac ture, equipment for 
manufacture and heat treatment, and conditions of time, temperature and atmosphere during heat treatment. 
3.6. batch non-metallic liners
: A "batch" shall be a group of  non-metallic liners 
successively produced having the same nominal diameter, wall thickness, design specified material of construction and process of manufacture. 
 3.7. batch limits
: In no case shall a "batch" be permitted to exceed 200 finished 
cylinders or liners (not including destructiv e test cylinders or liners), or one shift 
of successive production,  whichever is greater. 
 3.8. composite cylinder
: A cylinder made of resin impregnated continuous filament 
wound over a metallic or non-metallic liner. Composite cylinders using non-metallic liners are referred to as all-composite cylinders. 
 3.9. controlled tension winding
: A process used in manufacturing hoop wrapped 
composite cylinders with metal liners by which compressive stresses in the liner 
and tensile stresses in the over-wrap at zero internal pressure are obtained by 
winding the reinforcing filaments under significant high tension. 
 3.10. filling pressure
: The gas pressure in the cylinder immediately upon completion of 
filling. 
3.11. finished cylinders : Completed cylinders which are r eady for use, typical of normal 
production, complete with identification marks and external coating including 
integral insulation specified by the ma nufacturer, but free from non-integral 
insulation or protection. 
 3.12.  full-wrap
: An over-wrap having a filament wound reinforcement both in the 
circumferential and axial direction of the cylinder. 
 3.13.  gas temperature
: The temperature of gas in a cylinder. 
 3.14.  hoop-wrap
: An over-wrap having a filame nt wound reinforcement in a 
substantially circumferential pattern over the cylindrical portion of the liner so 
that the filament does not carry any significant load in a direction parallel to the cylinder longitudinal axis. 
 3.15. liner
: A container that is used as a gas-tight, inner shell, on which reinforcing 
fibres are filament wound to reach the n ecessary  strength.  Two types of liners are GSO STANDARD                                                                     GSO  /    
 
 40described in this standard: Metallic liners that are designed to share the load with 
the reinforcement, and non-metallic liners that do not carry any part of the load. 
 
3.16.  manufacturer : The person or organization respons ible for the design, fabrication 
and testing of the cylinders. 
 3.17.  maximum developed pressure
: The settled pressure developed when gas in a 
cylinder filled to the working pressure  is raised to the maximum service 
temperature. 
 3.18.  over-wrap
: The reinforcement system of filame nt and resin applied over the liner. 
 3.l9.  prestressing
: The process of applying auto-fre ttage or controlled tension winding. 
 3.20.  service life
: The life in years during which the cylinders may safely be used in 
accordance with the standard service conditions. 
 3.21.  settled pressure
: The gas pressure when a given settled temperature is reached. 
 3.22. settled temperature
: The uniform gas temperature after any change in temperature 
caused by filling has dissipated. 
 3.23.  test pressure
: The pressure at which the cylinder is hydrostatically tested. 
 3.24.  working pressure
: The settled pressure of 20 MPa at a uniform temperature of 15 
°C. 
 
4. SERVICE CONDITIONS 
 
4.1. General  
 4.1.1. Standard service conditions   The standard service conditions specified in this section are provided as a basis 
for the design, manufacture, inspection, tes ting, and approval of cylinders that are 
to be mounted permanently on vehicles a nd used to store natural gas at ambient 
temperatures for use as a fuel on vehicles. 
 
4.1.2. Use of cylinders   The service conditions specified are also  intended to provide information on how 
cylinders made to this Regulation may safely be used to: 
 
(a) manufacturers of cylinders; (b) owners of cylinders;  (c) designers or contractors responsible for the installation of cylinders; GSO STANDARD                                                                     GSO  /    
 
 
 41(d) designers or owners of equipment used to refuel vehicle cylinders; (e) suppliers of natural gas; and (f) regulatory authorities who have jurisdiction over cylinder use. 
 4.1.3. Service life 
  The service life for which cylinders are safe shall be specified by the cylinder 
designer on the basis of use under serv ice conditions specified herein. The 
maximum service life shall be 20 years. 
 4.1.4. Periodic requalification   Recommendations for periodic requalifica tion by visual inspection or testing 
during the service life shall be provided by the cylinder manufact urer on the basis 
of use under service conditions specified herein. Each cylinder shall be visually inspected at least every 48 months after th e date of its entry into service on the 
vehicle (vehicle registration), and at th e time of any re-installation, for external 
damage and deterioration, including under the support straps. The visual 
inspection shall be performed by a competent agency approved or recognized by the Regulatory Authority, in accordance w ith the manufacturers specifications:  
Cylinders without label containing manda tory information, or with labels 
containing mandatory information that are illegible in any way shall be removed from service. If the cylinder can be  positively identified by manufacturer and 
serial number, a replacement label may be applied, allowing the cylinder to remain in service. 
 
4.1.4.1. Cylinders involved in collisions 
  Cylinders which have been involved in a vehicle collision shall be reinspected by 
an agency authorized by the manufactur er, unless otherwise directed by the 
Authority having jurisdiction. Cylinder wh ich have not experienced any impact 
damage from the collision may be returned to service, otherwise the cylinder shall be returned to the manufacturer for evaluation. 
 4.1.4.2 Cylinders involved in fires   Cylinders which have been subject to the action of fire shall be reinspected by an 
agency authorized by the manufacturer, or condemned and removed from service. 
 4.2. Maximum pressures
 
 
 The cylinder pressure shall be limited to the following:  
(a) a pressure that would settle to 20 MPa at a settled temperature of 15 °C; 
(b) 26 MPa, immediately after filling, regardless of temperature; GSO STANDARD                                                                     GSO  /    
 
 42 
4.3. Maximum number of filling cycles  
  Cylinders are designed to be filled up to  a settled pressure of 20 MPa bar at a 
settled gas temperature of 15 °C for up to 1,000 times per year of service. 
 4.4. Temperature range
 
 4.4.1. Settled gas temperature   
 Settled temperature of gas in cylinders may vary from a minimum of -40 °C to a 
maximum of 65 °C; 
 
4.4.2. Cylinder temperatures 
 
 The temperature of the cylinder materi als may vary from a minimum of -40 °C 
to a maximum of +82 °C; 
  Temperatures over +65 °C may be sufficiently local, or of short enough duration, 
that the temperature of gas in the cylinder never exceeds +65 °C, except under the 
conditions of paragraph 4.4.3; 
 
4.4.3. Transient temperatures 
 Developed gas temperatures during filling and discharge may vary beyond the limits of paragraph 4.4.1; 
 4.5. Gas composition
 
 
 Methanol and/or glycol shall not be deliberately added to the natural gas. Cylinder 
should be designed to tolerate being filled with natural gas meeting either of the 
following three conditions: 
 
(a) SAE J1616 
 (b) Dry gas 
  Water vapour would normally be limited to less than 32 mg/m
3. a pressure 
dewpoint of -9 °C at 20 MPa. There would be no constituent limits for dry gas, 
except for: 
 
 Hydrogen sulfide and other soluble sulfides: 23 mg/m3 
 
 Oxygen: 1 per cent by volume   Hydrogen shall be limited to 2 per cent by volume when cylinders are GSO STANDARD                                                                     GSO  /    
 
 
 43manufactured from a steel with an ultimate tensile strength exceeding 950 MPa; 
  (c) Wet gas   Gas that contains a water content hi gher than b) normally meets the following 
constituent limits; 
 
 Hydrogen sulfide and other soluble sulfides: 23 mg/m
3 
 
 Oxygen: 1 per cent by volume   Carbon dioxide: 4 per cent by volume   Hydrogen: 0.1 per cent by volume 
 
 Under wet gas conditions, a minimum of 1 mg of compressor oil per kg of gas is 
necessary to protect metallic cylinders and liners. 
 4.6. External surfaces
 
 
 Cylinders are not designed for continuous  exposure to mechanical or chemical 
attack, e.g. leakage from cargo that may be  carried on vehicles or severe abrasion 
damage from road conditions, and sha ll comply with recognized installation 
standards. However, cylinder external surfaces may be inadvertently exposed to: 
 
(a) water, either by intermittent immersion or road spray; 
(b) salt, due to the operation of the vehi cle near the ocean or where ice melting 
salt is used; 
(c) ultra-violet radiation from sunlight; (d) impact of gravel; (e) solvents, acids and alkalis, fertilizers; and (f) automotive fluids, including gasoline, hydraulic fluids, glycol and oils. 
 4.7. Gas permeation or leakage
 
 
Cylinders may be located in enclosed spaces for extended periods of time. 
Permeation of gas through the cylinde r wall or leakage between the end 
connections and the liner shall be considered in the design. 
 GSO STANDARD                                                                     GSO  /    
 
 445. DESIGN APPROVAL 
 
5.1. General  
 
The following information shall be submitted by the cylinder designer with a request for approval to the Competent Authority: 
 
(a) statement of service (paragraph 5.2.) (b) design data (paragraph 5.3.) 
(c) manufacturing data (paragraph 5.4.) 
(d) quality system (paragraph 5.5.) (e) fracture performance and NDE (Non De structive Examination) defect size 
(paragraph 5.6.); 
(f) specification sheet (paragraph 5.7.) (g) additional supporting data (paragraph 5.8.)   For cylinders designed in accordance with ISO 9809 it is not required to 
provide the stress analysis report in paragraph 5.3.2. or the information in 
paragraph 5.6.  
 5.2. Statement of service
 
 
The purpose of this statement of service is to guide users and installers of 
cylinders as well as to inform the approving Competent Authority, or their 
designated representative. The statement of service shall include:  (a) a statement that the cylinder desi gn is suitable for use in the service 
conditions defined in paragraph 4 for the service life of the cylinder; 
(b) the service life; 
(c) the minimum in-service test and/or inspection requirements; (d) the pressure relief devices and/or insulation required; (e) support methods, protective coatings, etc., required but not provided; (f) a description of the cylinder design; (g) any other information necessary to en sure the safe use and inspection of the 
cylinder. 
 5.3. Design data
 
 
5.3.1. Drawings   Drawings shall show the following as a minimum:  
(a) Title, reference number, date of issue, and revision numbers with dates of 
issue if applicable; 
(b) Reference to this Regulation and the cylinder type; 
(c) All dimensions complete with tole rances, including details of end closure GSO STANDARD                                                                     GSO  /    
 
 
 45shapes with minimum thicknesses and of openings;   
(d) Mass, complete with tolerance, of cylinders; (e) Material specifications, complete with minimum mechanical and chemical 
properties or tolerance ranges and, for metal cylinders or metal liners, the specified hardness range;  
(f) Other data such as, auto-frettage pressure range, minimum test pressure, 
details of the fire protection system and of the exterior protective coating. 
 
5.3.2. Stress analysis report   A finite element stress analysis or other stress analysis shall be provided;   A table summarizing the calculated stresses in the report shall be provided.  5.3.3. Material test data   A detailed description of the materials a nd tolerances of the materials properties 
used in the design shall be provided. Test data shall also be presented characterizing the mechanical properties and the suitability of the materials for 
service under the conditions specified in paragraph 4. 
 5.3.4. Design qualification test data   The cylinder material, design, manufacture and examination shall be provided to 
be adequate for their intended service by meeting the requirements of the tests 
required for the particular cylinder design, when tested in accordance with the 
relevant methods of test detailed in Appendix A to this annex. 
 The test data shall also document the dimensions, wall thicknesses and weights of 
each of the test cylinders. 
 
5.3.5. Fire protection   The arrangement of pressure relief devices that will protect the cylinder from 
sudden rupture when exposed to the fire conditions in paragraph A.15 shall be specified. Test data shall substantiate the effectiveness of the specified fire 
protection system. 
 5.3.6. Cylinder supports   Details of cylinder supports or suppor t requirements shall be provided in 
accordance with paragraph 6.11. 
 5.4. Manufacturing data
 
 
 Details of all fabrication processes, non-destructive examinations, production tests GSO STANDARD                                                                     GSO  /    
 
 46and batch tests Shall be provided; The to lerances for all production processes such 
as heat treatment, end forming, resin mix ratio, filament winding tension and 
speed, curing times and temperatures, and auto-frettage procedures shall be 
specified; Surface finish, thread details, acceptance criteria for ultrasonic scanning 
(or equivalent), and maximum lot sizes for batch tests shall also be specified. 
 5.5. (not allocated) 
 
5.6. Fracture performance and NDE defect size
 
 
5.6.1. Fracture performance   The manufacturer shall demonstrate the Leak-Before-Break performance of the 
design as described in paragraph 6.7. 
 
5.6.2. NDE defect size 
   Using the approach described in paragraph 6.15.2 the manufacturer shall establish 
the maximum defect size for non-destruc tive examination which will prevent the 
failure of the cylinder during its service life due to fatigue, or failure of the 
cylinder by rupture. 
 5.7. Specification sheet
 
 
 A summary of the documents providing th e information required in paragraph 5.1. 
shall be listed on a specification sh eet for each cylinder design. The title, 
reference number, revision numbers and date s of original issue and version issues 
of each document shall be given. All documents shall be signed or initialled by the issuer; The specification sheet shall be given a number, and revision numbers if 
applicable, that can be used to designate the cylinder design and shall carry the 
signature of the engineer responsible for the design. Space shall be provided on 
the specification sheet for a stamp indicating registration of the design.  
 5.8. Additional supporting data
 
 
 Additional data which would support the application, such as the service history 
of material proposed for use, or the use of a particular cylinder design in other 
service conditions, shall be provided where applicable. 
 5.9. Approval and certification
 
 5.9.1. Inspection and testing   Evaluation of conformity is required to  be performed in accordance with the 
provisions of paragraph 9 of this Regulation; 
 GSO STANDARD                                                                     GSO  /    
 
 
 47 In order to ensure that the cylinders are in compliance with this international 
Regulation they shall be subject to inspection in accordance with paragraphs 6.13. and 6.14. performed by the Competent Authority. 
 5.9.2. Test certificate 
  If the results of prototype testing acco rding to paragraph 6.13. are satisfactory, the 
Competent Authority shall issue a test certif icate. An example of a test certificate 
is given in Appendix B to this annex. 
 5.9.3. Batch acceptance certificate   The Competent Authority shall prepare an acceptance certificate as provided in 
Appendix B to this annex. 
 
6. REQUIREMENTS APPLICABLE TO ALL CYLINDER TYPES 
 
6.1. General
 
 
 The following requirements are generally applicable to the cylinder types 
specified in paragraphs 7 to 10. The desi gn of cylinders shall cover all relevant 
aspects which are necessary to ensure th at every cylinder produced according to 
the design is fit for its purpose for the sp ecified service life; Type CNG-1 steel 
cylinders designed in accordance with ISO 9809 and meeting all the requirements 
therein are only required to meet the requirements of paragraphs 6.3.2.4. and 
6.9 to 6.13. 
 6.2. Design
 
 
 This Regulation does not provide design formulas nor permissible stresses or 
strains, but requires the adequacy of th e design to be established by appropriate 
calculations and demonstrated by cylinders  being capable of consistently passing 
the materials, design qualification, producti on and batch tests specified in this 
Regulation; All designs shall ensure a "leakage before break" failure mode under 
feasible degradation of pressure parts dur ing normal service. If leakage of metal 
cylinders or metal liners occurs, it shall be only by the growth of a fatigue crack. 
 
6.3. Materials  
 
6.3.1. Materials used shall be suitable for the service conditions specified in paragraph 
4. The design shall not have incompatible materials in contact. The design qualification tests for materials are summarised in table 6.1. 
 6.3.2. Steel 
 GSO STANDARD                                                                     GSO  /    
 
 486.3.2.1. Composition 
  Steels shall be aluminium and/or silic on killed and produced to predominantly 
fine grain practice. The chemical compos ition of all steels shall be declared and 
defined at least by: 
 
(a) carbon, manganese, aluminium and silicon contents in all cases; 
(b) nickel, chromium, molybdenum, boron and vanadium contents, and any 
other alloying elements intentionally added.  The following limits shall not 
be exceeded in the cast analysis: 
   
Tensile strength < 950 MPa ≥ 950 MPa 
Sulfur 0.020 per cent 0.010 per cent 
Phosphorus 0.020 per cent 0.020 per cent 
Sulfur and 
Phosphorus 0.030 per cent 0.025 per cent 
 
When a carbon-boron steel is used, a hard enability test in accordance with ISO 
642, shall be performed on the first and last i ngot or slab of each heat of steel. The 
hardness as measured in a distance of  7.9 mm from the quenched end, shall be 
within the range 33-53 HRC, or 327-560 HV, and shall be certified by the material manufacturer; 
 
6.3.2.2. Tensile properties 
  The mechanical properties of the steel in the finished cylinder or liner shall be 
determined in accordance with paragr aph A.1 (Appendix A). The elongation for 
steel shall be at least 14 per cent; 
 6.3.2.3. Impact properties   The impact properties of the steel in the finished cylinder or liner shall be 
determined in accordance with paragraph A.2 (Appendix A). Impact values shall 
not be less than that indicated in table 6.2 of this annex; 
 6.3.2.4. Bending properties   The bending properties of the welded stainl ess steel in the finished liner shall be 
determined in accordance with paragraph A.3. (Appendix A). 
 6.3.2.5. Macroscopic weld examination   A macroscopic weld examination for each  type of welding procedure shall be GSO STANDARD                                                                     GSO  /    
 
 
 49performed. It shall show complete fusion a nd shall be free of any assembly faults 
or unacceptable defects as specified according to level C in EN ISO 5817. 
 6.3.2.6. Sulfide stress cracking resistance  
 If the upper limit of the sp ecified tensile strength for the steel exceeds 950 MPa, 
the steel from a finished cylinder shall be  subjected to a sulphide stress cracking 
resistance test in accordance with Appendix A to this annex, item A.3. and meet the requirements listed therein. 
 6.3.3. Aluminium  6.3.3.1. Composition   Aluminium alloys shall be quoted in lin e with Aluminium Association practice for 
a given alloy system. The impurity limits for lead and bismuth in any aluminium alloy shall not exceed 0.003 per cent; 
 6.3.3.2. Corrosion tests   Aluminium alloys shall meet the requireme nts of the corrosion tests carried out in 
accordance with paragraph A.4 (Appendix A); 
6.3.3.3. Sustained load cracking   Aluminium alloys shall meet the requireme nts of the sustained load cracking tests 
carried out in accordance with paragraph A.5 (Appendix A); 
 6.3.3.4. Tensile properties   The mechanical properties of the aluminiu m alloy in the finished cylinder shall be 
determined in accordance with paragr aph A.l (Appendix A). The elongation for 
aluminium shall be at least 12 per cent. 
 6.3.4. Resins  6.3.4.1. General   The material for impregnation may be thermosetting or thermoplastic resins. 
Examples of suitable matrix material s are epoxy, modified epoxy, polyester and 
vinylester thermosetting plastics, and pol yethylene and polyamide thermoplastic 
material; 
 6.3.4.2. Shear strength   Resin materials shall be tested in accordance with paragraph A.26 (Appendix A), GSO STANDARD                                                                     GSO  /    
 
 50and meet the requirements therein; 
 
6.3.4.3. Glass transition temperature   The glass transition temperature of the resin material shall be determined in 
accordance with ASTM D3418. 
 
6.3.5. Fibres 
  Structural reinforcing filament material t ypes shall be glass fibre, aramid fibre or 
carbon fibre. If carbon fibre reinforcement is used the design shall incorporate 
means to prevent galvanic corrosion of metallic components of the cylinder. The 
manufacturer shall keep on file the published specifications for composite 
materials, the material manufacturer's recommendations for storage, conditions 
and shelf life and the material manufactur er's certification that each shipment 
conforms to said specification requireme nts. The fibre manufacturer shall certify 
that the fibre material properties confor m to the manufacturer's specifications for 
the product. 
 6.3.6 Plastic liners   The tensile yield strength and ultimate elongation shall be determined in 
accordance with paragraph A.22 (Appendi x A). Tests shall demonstrate the 
ductile properties of the plastic liner material at temperatures of -50 °C or lower 
by meeting the values specified by the ma nufacturer; The polymer ic material shall 
be compatible with the service conditions specified in paragraph 4 of this annex. 
In accordance with the method describe d in paragraph A.23 (Appendix A), the 
softening temperature shall be at least 90 °C, and the melting temperature at least 
100 °C. 
 6.4. Test pressure
 
 
 The minimum test pressure used in manufacture shall be 30 MPa;  6.5. Burst pressures and fibre stress ratios
 
  For all types of cylinder the minimum actual burst pressure shall not be less than 
the values given in table 6.3 of this annex. For type CNG- 2, CNG-3 and CNG-4 
designs the composite over-wrap shall be designed for high reliability under sustained loading and cyclic loading. This  reliability shall be achieved by meeting 
or exceeding the composite reinforcement st ress ratio values given in table 6.3 of 
this annex. Stress ratio is defined as th e stress in the fibre at the specified 
minimum burst pressure divided by the stre ss in the fibre at working pressure. The 
burst ratio is defined as the actual burst pressure of the cylinder divided by the 
working pressure; For type CNG-4 designs, the stress ratio is equal to the burst GSO STANDARD                                                                     GSO  /    
 
 
 51ratio; For type CNG-2 and CNG-3 designs  (metal-lined, composite over-wrapped) 
stress ratio calculations must include: 
 
(a) An analysis method with capability for non-linear materials (special purpose 
computer program or finite element analysis program); 
(b) Elastic-plastic stress-strain curve for liner material must be known and 
correctly modelled; 
(c) Mechanical properties of composite materials must be correctly modelled; 
(d) Calculations must be made at: auto-frettage, zero after auto-frettage, 
working and minimum burst pressures; 
(e) Prestresses from winding tension must be accounted for in the analysis; (f) Minimum burst pressure must be chos en such that the calculated stress at 
minimum burst pressure divided by the calculated stress at working pressure 
meets the stress ratio requirements for the fibre used;  
(g) When analyzing cylinders with hybrid reinforcement (two or more different 
fibre types), the load share between the different fibres must be considered 
based on the different elastic modulii of the fibres. The stress ratio requirements for each individual fibre t ype must be in accordance with the 
values given in table 6.3. of this anne x.  Verification of the stress ratios may 
also be performed using strain gauges. An acceptable method is outlined in the informative Appendix C to this annex.  
 6.6. Stress analysis
 
 
 A stress analysis shall be performe d to justify the minimum design wall 
thicknesses. It shall include the determination of the stresses in liners and fibres of 
composite designs. 
 6.7. Leak-before-break (LBB) assessment
  
  Types CNG-1, CNG-2 and CNG-3 cylinde rs shall demonstrate Leak-Before-
Break (LBB) performance. The LBB performance test shall be carried out in accordance with paragraph A.6 (Appendix A). Demonstration of LBB performance is not required for cylinde r designs that provide a fatigue life 
exceeding 45,000 pressure cycles when test ed in accordance with paragraph A.13 
(Appendix A). Two methods of LBB assessm ent are included for information in 
Appendix D to this annex. 
 
6.8. Inspection and testing
 
 
 The manufacturing inspection shall specify programmes and procedures for:  
(a) manufacturing inspection, tests and acceptance criteria; and (b) periodic in service inspection, tests and acceptance criteria. The interval of 
visual reinspection of the external cy linder surfaces shall be in accordance GSO STANDARD                                                                     GSO  /    
 
 52with paragraph 4.1.4. of this annex unless varied by the Competent 
Authority. The manufacturer shall estab lish the visual reinspection rejection 
criteria based on the results  of pressure cycling tests performed on cylinders 
containing flaws. A guide for manufacturer's instructions for handling, use and inspection is provided in Appendix E to this annex. 
6.9. Fire protection
 
  All cylinders shall be protected from fire with pressure relief devices. The 
cylinder, its materials, pressure relief devices and any added insulation or protective material shall be designed collectively to ensure adequate safety during fire conditions in the test specified in paragraph A.15 (Appendix A). 
 
 Pressure relief devices shall be tested in accordance with paragraph A.24 
(Appendix A). 
 
6.10. Openings
 
 
6.10.1. General   Openings are permitted in heads only. Cent re line of openings shall coincide with 
the longitudinal axis of the cylinder. Th reads shall be clean cut, even, without 
surface discontinuities, and to gauge. 
 
6.11. Cylinder supports
 
 
 The manufacturer shall specify the means by which cylinders shall be supported 
for installation on vehicles. The ma nufacturer shall also supply support 
installation instructions, including clam ping force and torque to provide the 
required restraining force but not cause unacceptable stress in the cylinder or 
damage to the cylinder surface. 
 
6.12. Exterior environmental protection  
 
 The exterior of cylinders shall meet the requirements of the environmental test 
conditions of paragraph A.14 (Appendix A) . Exterior protection may be provided 
by using any of the following: 
 
(a) a surface finish giving adequate  protection (e.g. metal sprayed on 
aluminium, anodizing); or 
(b) the use of a suitable fibre and matrix material (e.g. carbon fibre in resin); or  
(c) a protective coating (e.g. organic co ating, paint) that shall meet the 
requirements of paragraph A.9 (Appendix A). 
 GSO STANDARD                                                                     GSO  /    
 
 
 53 Any coatings applied to cylinders shall be such that the application process does 
not adversely affect the mechanical proper ties of the cylinder. The coating shall be 
designed to facilitate subsequent in service inspection and the manufacturer shall provide guidance on coating treatment dur ing such inspection to ensure the 
continued integrity of the cylinder. 
 
 Manufacturers are advised that an environmental performance test that evaluates 
the suitability of coating systems is pr ovided in the informative Appendix F to 
this annex. 
 6.13. Design qualification tests
 
 
 For the approval of each cylinder type  the material, design, manufacture and 
examination shall be proved to be adequate for their intended service by meeting the appropriate requirements of the material qualification tests summarized in table 6.1 of this annex and the cylinder qualification tests summarized in table 6.4 
of this annex, with all test s in accordance with the relevant methods of test as 
described in Appendix A to this annex. The test cylinders or liners shall be 
selected and the tests witnessed by the Co mpetent Authority. If more cylinders or 
liners are subjected to the tests than are required by this annex, all results shall be 
documented. 
 
6.14. Batch tests
 
 
 The batch tests specified in this anne x for each cylinder type shall be conducted 
on cylinders or liners taken from each batch of finished cylinders or liners. Heat 
treated witness samples shown to be repres entative of finished cylinders or liners 
may also be used. Batch tests required for each cylinder type are specified in 
table 6.5 of this annex. 
 
6.15. Production examinations and tests  
 
6.15.1. General  
Production examinations and tests shall be carried out on all cy linders produced in 
a batch. Each cylinder shall be examined  during manufacture and after completion 
by the following means: 
 
(a) ultrasonic scanning (or demonstrated equivalent) of metallic cylinders and 
liners in accordance with BS 5045, Part  1, Annex B, or demonstrated 
equivalent method, to confirm that th e maximum defect size present is 
smaller than the size specified in the design; 
(b) verification that the critical dimensions and mass of the completed cylinder 
and of any liner and over-wrapping are within design tolerances; 
(c) verification of compliance with sp ecified surface finish with special GSO STANDARD                                                                     GSO  /    
 
 54attention to deep drawn surfaces and folds or laps in the neck or shoulder of 
forged or spun end enclosures or openings; 
(d) verification of markings; (e) hardness tests of metallic cylinders and liners in accordance with 
paragraph .8 (Appendix A) shall be carried  out after the final heat treatment 
and the values thus determ ined shall be in the range specified for the design; 
(f) hydrostatic proof test in accordance with paragraph A.11 (Appendix A);  
 
A summary of critical production inspec tion requirements to be performed on 
every cylinder is provided in table 6.6 of this annex; 
 6.15.2. Maximum defect size   For type CNG-1, CNG-2 and CNG-3 desi gns, the maximum defect size at any 
location in the metal cylinder or metal liner  that will not grow to a critical size 
within the specified service life shall be  determined. The critical defect size is 
defined as the limiting through-wall (cylinder or liner) thickness defect that would allow stored gas to be discharged without  rupturing the cylinder. Defect sizes for 
the rejection criteria for ultrasonic scanning, or equivalent shall be smaller than the maximum allowable defect sizes. For type CNG-2 and CNG-3 designs assume 
that there shall be no damage to composite due to any time-dependent mechanisms; The allowable defect size for NDE shall be determined by an 
appropriate method. Two such methods are outlined in the informative Appendix D to this annex. 
 6.16. Failure to meet test requirements
 
 
 In the event of failure to meet test re quirements retesting or reheat treatment and 
retesting shall be carried out as follows: 
 
(a) if there is evidence of  a fault in carrying out a test, or an error of 
measurement, a further test shall be pe rformed. If the result of this test is 
satisfactory, the first test shall be ignored; 
(b) If the test has been carried out in a satisfactory manner, the cause of test 
failure shall be identified. 
 
If the failure is considered to be due to the heat treatment applied, the 
manufacturer may subject all the cylinders of  the batch to a further heat treatment. 
 
If the failure is not due to  the heat treatment applied, all the identified defective 
cylinders shall be rejected or repaired by an approved method. The non-rejected cylinders are then considered as a new batch.  In both cases the new batch shall be retest ed. All the relevant prototype or batch 
tests needed to prove the acceptability of the new batch shall be performed again. 
If one or more tests prove even partially  unsatisfactory, all cylinders of the batch GSO STANDARD                                                                     GSO  /    
 
 
 55shall be rejected. 
 6.17. Change of design
 
 
A design change is any change in the selection of structural materials or 
dimensional change not attributable to normal manufacturing tolerances.  Minor design changes shall be permitted to be qualified through a reduced test 
program. Changes of design specified  in table 6.7 shall require design 
qualification testing as specified in the table. 
 
Table 6.1.
 - Material design qualification test 
 
 Relevant paragraph of this annex 
 Steel Aluminium Resins Fibres Plastic liners
Tensile properties 6.3.2.2. 6.3.3.4.  6.3.5. 6.3.6. 
Impact properties 6.3.2.3.     
Bending properties 6.3.2.4.     
Weld examination 6.3.2.5.     
Sulfide stress cracking resistance 6.3.2.6.     
Sustained load crack resistance  6.3.3.3.    
Stress corrosion cracking  6.3.3.2.    
Shear strength   6.3.4.2.   
Glass transition temperature   6.3.4.3.   
Softening/Melting temperature     6.3.6. 
Fracture mechanics* / 6.7. 6.7.    
*/ Not required if flawed cylinder test approach in paragraph A.7. of Appendix A is used. 
 GSO STANDARD                                                                     GSO  /    
 
 56Table 6.2  - Impact test acceptable values 
 
Cylinder diameter D, mm > 140 ≤ 140 
Direction of testing transverse longitudinal 
Width of test piece, mm 3 - 5 > 5 - 7.5 > 7.5 - 10 3 to 5 
Test temperature, °C -50 -50 
Mean of 3 specimens 30 35 40 60 
Impact strength, J/cm²     
Individual specimen 24 28 32 48 
 
Table 6.3  - Minimum actual burst values and stress ratios 
 
 CNG-1 
All-metal CNG-2 
Hoop-wrapped CNG-3 
Fully-wrapped CNG-4 
All-composite 
 Burst 
pressure 
[MPa] Stress 
ratio 
[MPa] Burst 
pressure 
[MPa] Stress 
ratio 
[MPa] Burst 
pressure 
[MPa] Stress 
ratio 
[MPa] Burst 
pressure 
[MPa] 
All 
metal 45       
Glass  2.75 50 1) 3.65 70 1) 3.65 73 
Aramid  2.35 47 3.10 60 1) 3.1 62 
Carbon  2.35 47 2.35 47 2.35 47 
Hybrid  2) 2) 2) 
Note 1  - Minimum actual burst pressure.  In addition, calculations must be performed in 
accordance with paragraph 6.5. of this annex to confirm that the minimum stress ratio requirements are also met. Note 2
 - Stress ratios and burst pressures shall be calculated in accordance with paragraph 6.5. 
of this annex. 
 GSO STANDARD                                                                     GSO  /    
 
 
 57Table 6.4  - Cylinder design qualification tests  
 
Cylinder type  Test and annex reference CNG-1 CNG-2 CNG-3 CNG-4 
A.12 Burst A.13 Ambient temp/cycle A.14 Acid environment test A.15 Bonfire A.16 Penetration A.17 Flaw tolerance A.18 High temp. creep 
A.19 Stress rupture 
A.20 Drop test A.21 Permeation A.24 PRD performance A.25 Boss torque test A.27 Natural gas cycling A.6 LBB assesment A.7 Extreme temperature/cycle X * 
X * 
 
X X 
  
 
  
X 
  
X X 
X X X X X X 
X 
 
 
X 
  
X X X 
X X X X X X 
X 
X 
 
X 
  
X X X 
X X X X X X 
X 
X X X X X 
 
X 
X =  required 
*  =  Not required for cylinders designed to ISO 9809 (ISO 9809 already provides for these tests). 
 
Table 6.5  - Batch tests  
 
Cylinder type  Test and annex reference CNG-1 CNG-2 CNG-3 CNG-4 
A.12 Burst A.13 Ambient cycle A.1 Tensile A.2 Impact (steel) A.9.2 Coating *  X X X X X 
 X X 
X † X † 
X 
 X X 
X † X † 
X 
 X X 
  
X 
 
X  =  required *  =   Except where no protective coating is used †  =   Tests on liner material 
 GSO STANDARD                                                                     GSO  /    
 
 58Table 6.6  - Critical production inspection requirements  
 
Type CNG-1 CNG-2 CNG-3 CNG-4 
Inspection requirement     
Critical dimensions 
Surface finish Flaws (ultrasonic or equivalent) Hardness of metal cylinders and metal liners Hydrostatic proof test Leak test 
Markings X 
X X X X 
 
X X X X X X 
 
X X X X X X 
 
X X X 
  
X X X 
X  =  required 
 GSO STANDARD                                                                     GSO  /    
 
 
 59Table 6.7  - Change of design 
 
  Type of test 
 
 Design change Burst Hydro-static 
A.12 Cycling 
ambient temp: 
A.13 Environ-
mental  
A.14 Bonfire 
  
A.15 Flaw 
tole-rance 
 A.17 Penetra-
tion  
A.16 Stress 
rupture A.19 
High. temp:Creep A.18 Drop test A.20 Boss torque 
A.25 Permeation 
A.21 CNG 
Cycling A.27 PRD 
performan c
 
A.24 
Fibre manufacturer X X     X* X†  
Metallic cylinder or liner material X X X* X X* X X*   
Plastic liner material  X X     X†  
Fibre material X X X X X X X X†  
Resin material   X  X X X   
Diameter change 
≤ 20 per cent X X        
Diameter change 
> 20 per cent X X  X X* X    
Length change 
≤ 50 per cent X   X‡      
Length change 
> 50 per cent X X  X‡      
Working pressure change 
≤ 20 per cent @ X X        
Dome shape X X      X†  
Opening size X X        
Coating change   X       
End boss design        X†  
Change in manuf. 
process X X        
Pressure relief device    X     X 
 
X = requried * Test not required on metal (CNG-1) designs: 
† Test only required on all-composite (CNG-4) designs 
‡ Test only required when length increases @ Only when thickness change proportional to diameter and/or pressure change 
 GSO STANDARD                                                                     GSO  /    
 
 607. TYPE CNG-1 METAL CYLINDERS 
 
7.1. General  
 
The design shall identify the maximum size of  an allowable defect at any point in 
the cylinder which will not grow to a cr itical size within the specified retest 
period, or service life if no retest is specified, of a cylinder operating to the working pressure. Determination of leak -before-break (LBB) performance shall 
be done in accordance with the appropriate  procedures defined in paragraph A.6 
(Appendix A). Allowable defect size sha ll be determined in accordance with 
paragraph 6.15.2. above. 
 Cylinders designed in accordance with ISO 9809 and meeting all the requirements therein are only required to meet th e materials test requirements of 
paragraph 6.3.2.4. above and the design qua lification test requirements of 
paragraph 7.5., except paragraphs 7.5.2. and 7.5.3. below. 
 7.2. Stress analysis
 
 
 The stresses in the cylinder shall be calculated for 2 MPa, 20 MPa, test pressure 
and design burst pressure. The calculations  shall use suitable analysis techniques 
using thin-shell theory that takes into account out-of-plane bendi ng of the shell to 
establish stress distributions at the neck, transition regions and the cylindrical part of the cylinder. 
 
7.3. Manufacturing and production test requirements
 
 
7.3.1. General  
The ends of aluminium cylinders shall not be closed by a forming process. The base ends of steel cylinders which ha ve been closed by forming, except those 
cylinders designed in accordance with ISO 9809, shall be NDE inspected or 
equivalent. Metal shall not be added in the process of closure at the end. Each 
cylinder shall be examined before end forming operations for thickness and 
surface finish.  After end forming the cylinders shall be  heat treated to the hardness range 
specified for the design. Localized heat treatment is not permitted.  When a neck ring, foot ring or attachment s for support are provided, it shall be of 
material compatible with that of the cylinder and shall be securely attached by a method other than welding, brazing or soldering. 
 GSO STANDARD                                                                     GSO  /    
 
 
 617.3.2. Non-destructive examination  
The following tests shall be carried out on each metallic cylinder:  (a) Hardness test in accordance with paragraph A.8 (Appendix A), 
(b) Ultrasonic examination, in accordan ce with BS 5045, Part 1, Annex I, or 
demonstrated equivalent NDT method, to  ensure that the maximum defect 
size does not exceed the size specified in the design as determined in accordance with paragraph 6.15.2. above. 
 7.3.3. Hydrostatic pressure testing   Each finished cylinder shall be hydrostati cally pressure tested  in accordance with 
paragraph A.11 (Appendix A). 
 7.4. Cylinder batch tests
 
 
 Batch testing shall be conducted on finish ed cylinders which are representative of 
normal production and are complete with identification marks. Two cylinders shall be randomly selected from each batch. If more cylinders are subjected to the 
tests than are required by this annex, all results shall be documented. The 
following tests shall as a minimum be carried out on these. 
 
(a) Batch materials tests. One cylinder, or a heat treat witness sample 
representative of a finished cylinder, shall be subjected to the following 
tests: (i) Critical dimensions checked against the design; (ii) One tensile test in accordance with paragraph A.1 (Appendix A) and 
meet the requirements of the design; 
(iii) For steel cylinders, three impact  tests in accordance with  paragraph 
A.2 (Appendix A) and meet the requirements of paragraph 6.3.2.3. 
above; 
(iv) When a protective coating is a pa rt of the design, the coating shall be 
tested in accordance with paragraph A.9.2 (Appendix A); 
 
All cylinders represented by a batch test which fail to meet the specified requirements shall follow the procedur es specified in paragraph 6.16. above. 
 Where the coating fails to meet the requirements of paragraph A.9.2 
(Appendix A), the batch shall be 100 per cent inspected to remove similarly defective cylinders. The coating on all defective cylinders may be stripped 
and recoated. The coating batch test shall then be repeated;  
 GSO STANDARD                                                                     GSO  /    
 
 62(b) Batch burst test. One cylinder shall be  hydrostatically pressurized to burst in 
accordance with paragraph A.12 (Appendix A). 
 
If the burst pressure is less than the minimum calculated burst pressure the 
procedures specified in paragraph 6.16. above shall be followed. 
 
(c) Periodic pressure cycling test. Finished cylinders shall be pressure cycled in 
accordance with paragraph A.13 (Appendix A) at a test frequency defined 
as follows: 
(i) one cylinder from each batch shall be pressure cycled for a total of 
1,000 times the specified service life in years, with a minimum 15,000 cycles; 
(ii) on 10 sequential production batches of a design family (i.e. similar 
materials and processes), should none of the pressure cycled cylinders 
in (i) above leak or rupture in  less than 1,500 cycles times the 
specified life in years (minimum  22,500 cycles) then the pressure 
cycle test can be reduced to one cylinder from every 5 batches of production;  
(iii) on 10 sequential production batche s of a design family, should none 
of the pressure cycled cylinders in (i) above leak or rapture in less than 2,000 cycles times the specified service life in years (minimum 30,000 cycles) then the pressure cycl e test can be reduced to one 
cylinder from every 10 batches of production; 
(iv) should more than 6 months have  expired since the last batch of 
production. then a cylinder from the next batch of pr oduction shall be 
pressure cycle tested in order to maintain the reduced frequency of 
batch testing in (ii) or (iii) above. 
(v) should any reduced frequency pressu re cycle test cylinder in (ii) or 
(iii) above fail to meet the required number of pressure cycles (minimum 22,500 or 30,000 pressure cycles, respectively,) then it shall be necessary to repeat the batc h pressure cycle test frequency in 
(i) for a minimum 10 production batches in order to re-establish the reduced frequency of batch pressure cy cle testing in (ii) or (iii) above. 
(vi) should any cylinder in (i), (ii), or  (iii) above fail to meet the minimum 
cycle life requirement of 1,000 cycles  times the specified service life 
in years (minimum 15,000 cycles), then the cause of failure shall be determined and corrected following the procedures in paragraph 6.16. The pressure cycle test shall then be repeated on an additional three 
cylinders from that batch. Should any of the three additional cylinders fail to meet the minimum pressu re cycling requirement of 1,000 
cycles times the specified service life in years, then the batch shall be 
rejected. 
 GSO STANDARD                                                                     GSO  /    
 
 
 637.5. Cylinder design qualification tests  
 7.5.1. General   Qualification testing shall be conducted on finished cylinders which are 
representative of normal production and co mplete with identification marks. 
Selection, witnessing and documentation of the results shall be in accordance with 
paragraph 6.13. above. 
 
7.5.2. Hydrostatic pressure burst test   Three representative cylinders shall be hydrostatically pressurised to failure in 
accordance with paragraph A.12. (Appendix A to this annex). The cylinder burst 
pressures shall exceed the minimum burst pressure calculated by the stress analysis for the design, and shall be at least 45 MPa. 
 7.5.3. Ambient temperature pressure cycling test.   Two finished cylinders shall be pressure cycled at ambient temperature in 
accordance with paragraph A.13 (Appendix A) to failure, or to a minimum of 45,000 cycles. The cylinders shall not fail before reaching the specified service 
life in years times 1,000 cycles. Cyli nders exceeding 1,000 cycles times the 
specified service life in years shall fail by leakage and not by rupture. Cylinders 
which do not fail within 45,000 cycles shall be destroyed either by continuing the cycling until failure occurs, or by hydros tatically pressurising to burst. The 
number of cycles to failure and the location of the failure initiation shall be recorded. 
 7.5.4. Bonfire test   Tests shall be conducted in accordance with paragraph A.15 (Appendix A) and 
meet the requirements therein. 
 7.5.5. Penetration test   Test shall be conducted in accordance with paragraph A.16 (Appendix A) and 
meet the requirements therein. 
 7.5.6. LBB performance   For cylinder designs not exceeding 45,000 cy cles when tested as per paragraph 
7.5.3. above, LBB performance tests shall be conducted in accordance with A.6 
and meet the requirements therein. 
8. TYPE CNG-2 HOOP-WRAPPED CYLINDERS  GSO STANDARD                                                                     GSO  /    
 
 648.1. General  
 
During pressurisation, this type of cyli nder design has a behaviour in which the 
displacements of the composite over-w rap and the metal liner are linearly 
superimposed. Due to different technique s of manufacture, this annex does not 
give a definite method for design. 
 
Determination of the leak-before-break (L BB) performance shall be in accordance 
with the appropriate procedures de fined in paragraph A.6 (Appendix A). 
Allowable defect size shall be determ ined in accordance with paragraph 6.15.2. 
above. 
 
8.2. Design requirements  
 
8.2.1. Metal liner   The metal liner shall have a minimum actual burst pressure of 26 MPa.  8.2.2. Composite over-wrap 
 
The tensile stress in the fibres shall meet the requirements of paragraph 6.5. 
above. 
 8.2.3. Stress analysis  
The stresses in the composite and in the liner after prestress shall be calculated. 
The pressures used for these calculations shall be zero, 2 MPa, 20 MPa test pressure and design burst pressure. The calculations shall use suitable analysis techniques using thin-shell theory taking account of non-linear material behaviour 
of the liner to establish stress distributi ons at the neck, transition regions and the 
cylindrical part of the liner.  For designs using auto-frettage to provide prestress, the limits within which the auto-frettage pressure must fall shall be calculated.  For designs using controlled tension winding to provide prestress, the temperature 
at which it is performed, the tension requi red in each layer of composite and the 
consequent prestress in the liner shall be calculated. 
 8.3. Manufacturing requirements
 
 
8.3.1. General   The composite cylinder shall be fabr icated from a liner over-wrapped with 
continuous filament windings. Filament wi nding operations shall be computer or 
mechanically controlled. The filaments shall be applied under controlled tension GSO STANDARD                                                                     GSO  /    
 
 
 65during winding. After winding is complete, thermosetting resins shall be cured by 
heating, using a predetermined and controlled time-temperature profile. 
 8.3.2. Liner  
 The manufacture of a metallic liner sh all meet the requirements given under 
paragraph 7.3. above for the appropriate type of liner construction. 
 8.3.3. Over-wrap   The cylinders shall be fabricated in a filament winding machine. During winding 
the significant variables shall be monitored within specified tolerances, and documented in a winding record. These va riables can include but are not limited 
to: 
 
(a) fibre type including sizing; (b) manner of impregnation; (c) winding tension; (d) winding speed;  (e) number of rovings; (f) band width; (g) type of resin and composition; (h) temperature of the resin; (i) temperature of the liner. 
 8.3.3.1. Curing of thermosetting resins 
 
If a thermosetting resin is used, the resi n shall be cured after filament winding. 
During the curing, the curing cycle (i.e. th e time-temperature history) shall be 
documented. 
The curing temperature shall be controlled and shall not affect the material properties of the liner. The maximum cu ring temperature for cylinders with 
aluminium liners is 177 °C. 
 8.3.4. Auto-frettage   Auto-frettage, if used, shall be carried out before the hydrostatic pressure test. The 
auto-frettage pressure shall be within  the limits established in paragraph 8.2.3. 
above, and the manufacturer shall establis h the method to verify the appropriate 
pressure. 
 8.4. Production test requirements
 
 
8.4.1. Non-destructive examination  GSO STANDARD                                                                     GSO  /    
 
 66 Non-destructive examinations shall be ca rried out in accordance with a recognized 
ISO or an equivalent standard. The follo wing tests shall be carried out on each 
metallic liner: 
 
(a) Hardness test in accordance with paragraph A.8 (Appendix A); 
(b) Ultrasonic examination, in accordan ce with BS 5045, Part 1, Annex 1B, or 
demonstrated equivalent NDT method, to  ensure that the maximum defect 
size does not exceed the size specified in the design. 
 
8.4.2. Hydrostatic pressure testing   Each finished cylinder shall be hydrostati cally pressure tested  in accordance with 
paragraph A.11 (Appendix A). The manufactur er shall define the appropriate limit 
of permanent volumetric expansion for the test pressure used, but in no case shall the permanent expansion exceed 5per cent of the total volumetric expansion at test 
pressure. Any cylinders not meeting the defined rejection limit shall be rejected and either destroyed or used for batch rest purposes. 
 8.5. Cylinder batch tests
 
 
8.5.1. General    Batch testing shall be conducted on finish ed cylinders which are representative of 
normal production and are complete with id entification marks. Two cylinders, or a 
cylinder and a liner as appropriate, shall be randomly selected from each batch. If 
more cylinders are subjected to the tests than are required by this annex, all results 
shall be documented. The following tests shall as a minimum be carried out on 
these. 
 
Where defects are detected in over-w rapping before any auto-frettage or 
hydrostatic pressure testing, the over-wra pping may be completely removed and 
replaced; 
 
(a) Batch materials tests. One cylinder, or liner, or heat treat witness sample 
that is representative of a finished cylinder, shall be subjected to the 
following tests: 
(i) Dimensions checked against the design;  (ii) One tensile test in accordance with paragraph A.1 (Appendix A) and 
meet the requirements of the design;  
(iii) For steel liners, three impact tests in accordance with paragraph A.2 
(Appendix A) and meet the requirements of the design;  
(iv) When a protective coating is a pa rt of the design, the coating shall be 
tested in accordance with paragra ph A.9.2 (Appendix A) and meet the 
requirements therein. All cylinders or liners represented by a batch 
test which fails to meet the requi rements specified shall follow the 
procedures specified in paragraph 6.16. above. GSO STANDARD                                                                     GSO  /    
 
 
 67 
Where the coating fails to meet the requirements of paragraph A.9.2. (Appendix A), the batch shall be 100 per cent inspected to remove similarly 
defective cylinders. The coating on all defective cylinders may be stripped 
using a method that does not affect th e integrity of the composite wrapping, 
and recoated. The coating batch test shall then be repeated. 
 
(b) Batch burst test. One cylinder shall be tested in accordance with the 
requirements of paragraph 7.4(b) above;  
(c) Periodic pressure cycling test. In  accordance with the requirements of 
paragraph 7.4(c) above. 
 
8.6. Cylinder design qualification tests
 
 
8.6.1. General   Qualification testing shall be conducted on cylinders which are representative of 
normal production and complete with identification marks. Selection, witnessing and documentation of the results shall comply with paragraph 6.13. above. 
 
8.6.2. Hydrostatic pressure burst test  
(a) One liner shall be hydrostatically burst in accordance with paragraph A.12. 
(Appendix A). The burst pressure sha ll exceed the minimum burst pressure 
specified for the liner design;  
(b) Three cylinders shall be hydrostatica lly burst in accordance with paragraph 
A.12 (Appendix A). Cylinder burst pre ssures shall exceed the specified 
minimum burst pressure established by the stress analysis for the design, in 
accordance with table 6.3, and in no case less than the value necessary to 
meet the stress ratio requirements of paragraph 6.5 above. 
 8.6.3. Ambient temperature pressure cycling test   Two finished cylinders shall be pressure  cycle tested at ambient temperature in 
accordance with paragraph A.13 (Appendix A) to failure, or to a minimum of 45,000 cycles. The cylinders shall not fail before reaching the specified service 
life in years times 1,000 cycles. Cyli nders exceeding 1000 cycles times the 
specified service life in years shall fail by leakage and not by rupture. Cylinders 
which do not fail within 45,000 cycles shall be destroyed either by continuing the cycling until failure occurs, or by hydrosta tically pressurizing to burst. Cylinders 
exceeding 45,000 cycles are permitted to fail by rupture. The number of cycles to failure and the location of the failure initiation shall be recorded. 
 8.6.4. Acid environment test  GSO STANDARD                                                                     GSO  /    
 
 68 One cylinder shall be tested in accord ance with paragraph A.14 (Appendix A) and 
meet the requirements therein. An optional environmental test is included in the 
informative Appendix F to this annex. 
 
8.6.5. Bonfire test   Finished cylinders shall be tested in accordance with paragraph A.15 (Appendix 
A) and meet the requirements therein. 
 
8.6.6. Penetration test   One finished cylinder shall be test ed in accordance with paragraph A.16 
(Appendix A) and meet the requirements therein. 
 8.6.7. Flaw tolerance tests   One finished cylinder shall be test ed in accordance with paragraph A.17 
(Appendix A) and meet the requirements therein. 
 8.6.8. High temperature creep test   In designs where the glass transition temperature of the resin does not exceed the 
maximum design material temperature by at least 20 °C, one cylinder shall be 
tested in accordance with paragraph A.18 (Appendix A) and meet the requirements therein. 
 
8.6.9. Accelerated stress rupture test  
  One finished cylinder shall be test ed in accordance with paragraph A.19 
(Appendix A) and meet the requirements therein. 
 8.6.10. LBB performance   For cylinder designs not exceeding 45,000 cy cles when tested as per paragraph 
8.6.3. above, LBB performance tests shall be conducted in accordance with A.6 
and meet the requirements therein. 
 8.6.11. Extreme temperature pressure cycling test  
 One finished cylinder shall be tested in accordance with paragraph A.7 (Appendix 
A) and meet the requirements therein. 
 
9. TYPE CNG-3 FULLY-WRAPPED CYLINDERS 
 
9.1. General
 
 GSO STANDARD                                                                     GSO  /    
 
 
 69 During pressurisation, this type of cylinder has a behaviour in which the 
displacements of the composite over-wrap and the liner are superimposed. Due to 
different techniques of manufacture, this  annex does not give a definite method 
for design; Determination of  the leak-before-break (LBB) performance shall be in 
accordance with the appropriate procedures defined in paragraph A.6 
(Appendix A). Allowable defect size shall be determined in accordance with paragraph 6.15.2. above. 
 9.2. Design requirements
 
 
9.2.1. Metal liner   
 The compressive stress in the liner at zero pressure and 15 °C shall not cause the 
liner to buckle or crease. 
 
9.2.2. Composite over-wrap   The tensile stress in the fibres shall meet the requirements of paragraph 6.5. 
above. 
 9.2.3. Stress analysis   The stresses in the tangential and longit udinal direction of the cylinder in the 
composite and in the liner after pressure shall be calculated. The pressure used for 
these calculations shall be zero, working pressure, 10 per cent of working pressure, test pressure and design burst pressure. The limits within which autofrettaging pressure must fall shall be calculated, The calculations shall use suitable analysis techniques using thin-shell theory taking account of non-linear material behaviour of the liner to esta blish stress distributions at the neck, 
transition regions and the cylindrical part of the liner. 
 9.3. Manufacturing requirements
 
 
Manufacturing requirements shall be in  accordance with paragraph 8.3. above 
except that the over-wrap shall also include helically wound filaments. 
 
9.4. Production test requirements  
  Production test requirements shall be in accordance with the requirements of 
paragraph 8.4. above. 
 9.5. Cylinder batch tests
 
  The batch tests shall be in accordance with the requirements of paragraph 8.5. 
above. GSO STANDARD                                                                     GSO  /    
 
 70 
9.6. Cylinder design qualification tests   
  Cylinder design qualification tests shall be  in accordance with the requirements of 
paragraph 8.6. above, and paragraph 9.6.1. belo w, except that the liner burst in 
paragraph 8.6. above is not required. 
 9.6.1. Drop test 
 
 One or more finished cylinders sh all be drop tested in accordance with 
paragraph A.30 (Appendix A). 
 10. TYPE CNG-4 ALL-COMPOSITE CYLINDERS  10.1. General
 
 
 This annex does not give a definite method for the design of cylinders with 
polymeric liners because of the variety of cylinder designs possible. 
 10.2. Design requirements
 
 
Design calculations shall be used to provi de justification of design adequacy. The 
tensile stresses in the fibres shall meet  the requirements of paragraph 6.5. above. 
Tapered and straight threads in accordance with paragraph 6.10.2. or 6.10.3. above shall be used on the metal end bosses. Metal end bosses with threaded openings sha ll be able to withstand a torque force 
of 500 Nm, without damaging the integrity  of the connection to the non-metallic 
liner. The metal end bosses connected to the non-metallic liner shall be of a 
material compatible with the service cond itions specified in paragraph 4 of this 
annex. 
 10.3. Stress analysis
  
 
 The stresses in the tangential and longit udinal direction of the cylinder in the 
composite and in the liner shall be calculated. The pressures used for these calculations shall be zero, working pressure, test pressure and design burst pressure. The calculations sh all use suitable analysis techniques to establish stress 
distribution throughout the cylinder. 
 
10.4. Manufacturing requirements
 
 
 Manufacturing requirements shall be in accordance with paragraph 8.3. above 
except that the curing temperature for thermosetting resins shall be at least 10 °C 
below the softening temperature of the plastic liner. 
 GSO STANDARD                                                                     GSO  /    
 
 
 7110.5. Production test requirements  
 10.5.1. Hydrostatic pressure testing   Each finished cylinder shall be hydrostati cally pressure tested  in accordance with 
paragraph A.11 (Appendix A). The manufactur er shall define the appropriate limit 
of elastic expansion for the test pressure  used, but in no case shall the elastic 
expansion of any cylinder exceed the av erage batch value by more than 10 per 
cent. Any cylinders not meeting the define d rejection limit shall be rejected and 
either destroyed or used for batch test purposes. 
 
10.5.2. Leak testing    Each finished cylinder shall be leak tested in accordance with paragraph A.10 
(Appendix A) and meet the requirements therein. 
 10.6. Cylinder batch tests
 
 
10.6.1. General   Batch testing shall be conducted on finish ed cylinders which are representative of 
normal production and are complete with id entification marks. One cylinder shall 
be randomly selected from each batch. If mo re cylinders are subjected to the tests 
than are required by this annex, all re sults shall be documented. The following 
tests shall as a minimum be carried out on these. 
 
(a) Batch materials test 
 
One cylinder, or liner, or liner witne ss sample that is representative of a 
finished cylinder, shall be subjected to the following tests:  (i) Dimensions checked against the design;  (ii) One tensile test of the plastic liner in accordance with paragraph A.22 
(Appendix A) and meet the requirements of the design; 
(iii) The melt temperature of the plastic liner shall be tested in accordance 
with paragraph A.23 (Appendix A), a nd meet the requirements of the 
design; 
(iv) When a protective coating is a pa rt of the design, the coating shall be 
tested in accordance with paragr aph A.9.2 (Appendix A). Where the 
coating fails to meet the re quirements of paragraph A.9.2 
(Appendix A), the batch shall be 100 per cent inspected to remove 
similarly defective cylinders. The coating on all defective cylinders may be stripped using a method that does not affect the integrity of the composite wrapping, and recoated. The coating batch test shall then be repeated. GSO STANDARD                                                                     GSO  /    
 
 72 
(b) Batch burst test   
 
One cylinder shall be tested in accordance with the requirements of 
paragraph 7.4(b) above; 
 (c) Periodic pressure cycling test 
 
On one cylinder the end boss shall be torque tested to 500 Nm in 
accordance with the test method in  paragraph A.25 (Appendix A). The 
cylinder shall then be pressure cy cle tested in accordance with the 
procedures provided in paragraph 7.4(c) above. 
 
Following the required pressure cycling, th e cylinder shall be leak tested in 
accordance with the method described in paragraph A.10 (Appendix A) and 
meet the requirements therein. 
 
10.7. Cylinder design qualification tests
 
 
10.7.1. General   Cylinder design qualification tests shall be  in accordance with the requirements of 
paragraphs 8.6., 10.7.2., 10.7.3. and 10.7.4. of th is annex, except that the LBB 
performance in paragraph 8.6.10. above is not required. 
 
10.7.2. Boss torque test    One cylinder shall be tested in accordance with paragraph A.25 (Appendix A).  10.7.3. Permeation test   One cylinder shall be tested for perm eation in accordance with paragraph A.21 
(Appendix A) and meet the requirements therein. 
 10.7.4. Natural gas cycling test   One finished cylinder shall be test ed in accordance with paragraph A.27 
(Appendix A) and meet the requirements therein. 
 GSO STANDARD                                                                     GSO  /    
 
 
 7311. MARKING 
 
11.1. Provision of marking  
  On each cylinder the manufacturer shall provide clear permanent markings not 
less than 6 mm high. Marking shall be made  either by labels incorporated into 
resin coatings, labels attached by adhesive, low stress stamps used on the thickened ends of type CNG-1 and CNG- 2 designs, or any combination of the 
above. Adhesive labels and their appli cation shall be in accordance with ISO 
7225, or an equivalent Standard. Multiple labels are allowed and should be 
located such that they are not obscu red by mounting brackets. Each cylinder 
complying with this annex shall be marked as follows: 
 
(a) Mandatory information:  
(i) "CNG ONLY"; (ii) "DO NOT USE AFTER XX/XXXX" , where "XX/XXX" identifies 
the month and year of expiry 1
/; 
(iii) Manufacturer’s identification; 
(iv) Cylinder identification (applicable part number and a serial number 
unique for every cylinder); 
(v) Working pressure and temperature; (vi) ECE Regulation number, along w ith cylinder type and certification 
registration number; 
(vii) The pressure relief devices and/or valves which are qualified for use 
with the cylinder, or the means for obtaining information on qualified 
fire protection systems;  
(viii) When labels are used, all cylinders shall have a unique identification 
number stamped on an exposed metal surface to permit tracing in the 
event that the label is destroyed; 
 (b) Non-mandatory information:  
On a separate label(s) the following non-mandatory information may be provided: 
(i) Gas temperature range, e.g. -40 °C to 65 °C; 
(ii) Nominal water capacity of the cylinder to two significant numbers. 
e.g. 120 litres; 
(iii) Date of original pressure test (month and year). 
The markings shall be placed in the liste d sequence but the specific arrangement 
may be varied to match the space available. An acceptable example of mandatory 
information is: 
                    
 
1/ The expiry date shall not exceed the specified service life. The expiry date may be applied 
to the cylinder at the time of dispatch, provided that the cylinders have been stored in a dry 
location without internal pressure. GSO STANDARD                                                                     GSO  /    
 
 74 
 
CNG ONLY DO NOT USE AFTER ../.... Manufacturer/Part Number/Serial Number  
20 MPa/15 °C  
ECE R 110 CNG-2 (registration No.)  
"Use Only Manufacturer-Approved Pressure Relief Device"   
 
12. PREPARATION FOR DISPATCH 
 
Prior to dispatch from the manufacturers shop, every cylinder shall be internally 
clean and dried. Cylinders not immediatel y closed by the fitting of a valve, and 
safety devices if applicable, shall have plugs, which prevent entry of moisture and 
protect threads, fitted to all openings. A corrosion inhibitor (e.g. oil-containing) 
shall be sprayed into all steel cylinders and liners prior to dispatch. 
 The manufacturer's statement of service a nd all necessary information to ensure 
the proper handling, use and in-service inspection of the cylinder shall be supplied to the purchaser. The statement shall be  in accordance with Appendix B to this 
annex. 
   GSO STANDARD                                                                     GSO  /    
 
 
Annex 2 - Appendix A  
 
TEST METHODS 
 A.1. Tensile tests, steel and aluminium
 
  A tensile test shall be carried out on the ma terial taken from the cylindrical part of 
the finished cylinder using a rectangular test piece shaped in accordance with the 
method described in ISO 9809 for steel and ISO 7866 for aluminium.  For cylinders with welded stainless steel liners,  tensile tests shall be also carried out 
on material taken from the welds in accordance with the method described in 
paragraph 8.4. of EN 13322-2.  The two faces of the test pieces representing the 
inside and outside surface of the cylinder sh all not be machined.  The tensile test 
shall be carried out in accordance with ISO 6892. 
 
 NOTE - Attention is drawn to the method of measurement of elongation described 
in ISO 6892, particularly in cases where the tensile test piece is tapered, resulting in a point of fracture away from the middle of the gauge length. 
 A.2. Impact test, steel cylinders and steel liners
 
 
 The impact test shall be carried out on the material taken from the cylindrical part 
of the finished cylinder on three test  pieces in accordance with ISO 148.  The 
impact test pieces shall be taken in the direction as required in table 6.2 of Annex 
2 from the wall of the cylinder.  For cyli nders with welded stainless steel liners, 
impact tests shall be also carried out  on material taken from the weld in 
accordance with the method described in paragraph 8.6. of EN 13322-2.  The 
notch shall be perpendicular to the face of  the cylinder wall. For longitudinal tests 
the test piece shall be machined all over (on six faces), if the wall thickness does 
not permit a final test piece width of 10 mm, the width shall be as near as 
practicable to the nominal thickness of th e cylinder wall. The test pieces taken in 
transverse direction shall be machined on four faces only, the inner and outer face 
of the cylinder wall unmachined. 
 A.3.  Sulphide stress cracking test for steel
 
 
Except as identified in the following, tes ting shall be conducted in accordance 
with Method A-NACE Standard Tensile Te st procedures, as described in NACE 
Standard TM0177-96. Tests shall be condu ced on a minimum of three tensile 
specimens with a gauge diameter of 3.81 mm (0.150 inches) machined from the 
wall of a finished cylinder or liner.  The specimens shall be placed under a 
constant tensile load equal to 60 per cen t of the specified minimum yield strength 
of the steel, immersed in a solution of  distilled water buffered with 0.5 per cent 
(mass fraction) sodium acetate trihydrate and adjusted to an initial pH of 4.0, 
using acetic acid.   The solution shall be continuously satura ted at room temperature and pressure 
with 0.414 kPa (0.06 psia) hydrogen sulphide  (balance nitrogen).  The tested GSO STANDARD                                                                     GSO  /    
 
 
 76specimens shall not fail within a test duration of 144 hours. 
 A.4. Corrosion tests, aluminium
 
  Corrosion tests for aluminium alloys shall be carried out in accordance with 
Annex A of ISO/DIS 7866 and meet the requirements therein. 
 A.5. Sustained load cracking tests, aluminium
 
  The resistance to SLC shall be carri ed out in accordance with Annex D of 
ISO/DIS 7866 and shall meet the requirements therein; 
 A.6. Leak-Before-Break (LBB) performance test
 
 
Three finished cylinders shall be pressu re cycled between not more than 2 MPa 
and nor less than 30 MPa at a rate not to exceed 10 cycles per minute.   All cylinders shall fail by leakage. 
 
A.7. Extreme temperature pressure cycling
 
 
 Finished cylinders, with the composite  wrapping free of any protective coating, 
shall be cycle tested, without showing ev idence of rupture, leakage, or fibre 
unravelling, as follows: 
 
(a) Condition for 48 hours at zero pressure, 65 °C or higher, and 95 per cent or 
greater relative humidity. The intent of  this requirement shall be deemed 
met by spraying with a fine spray or mi st of water in a chamber held at 65 
°C; 
(b) Hydrostatically pressurized for 500 cycl es times the specified service life in 
years between not more than 2 MPa and not less than 26 MPa at 65 ° or 
higher and 95 per cent humidity; 
(c) Stabilize at zero pressure and ambient temperature; 
(d) Then pressurize from not more than 2 MPa to not less than 20 MPa for 500 
cycles times the specified service life in years at -40 °C or lower; 
 The pressure cycling rate of b) sha ll not exceed 10 cycles per minute. The 
pressure cycling rate of d) shall not ex ceed 3 cycles per minute unless a pressure 
transducer is installed directly with in the cylinder. Adequate recording 
instrumentation shall be provided to ensu re the minimum temper ature of the fluid 
is maintained during the low temperature cycling.   Following pressure cycling at extreme temperatures, cylinders shall be hydrostatically pressured to failure in accordance with the hydrostatic burst test 
requirements, and achieve a minimum burst pressure of 85 per cent of the GSO STANDARD                                                                     GSO  /    
 
 
 77minimum design burst pressure. For type CNG-4 designs, prior to the hydrostatic 
burst test the cylinder shall be leak tested in accordance with paragraph A.10 below. 
 A.8. Brinell hardness test
 
  Hardness tests shall be carried out on th e parallel wall at the centre and a domed 
end of each cylinder or liner in accord ance with ISO 6506. The test shall be 
carried out after the final heat treatment and the hardness values thus determined 
shall be in the range specified for the design. 
 
A.9. Coating tests
 (mandatory if paragraph 6.12 c) of Annex 2 is used) 
 
A.9.1. Coating performance tests   Coatings shall be evaluated using the following test methods, or using equivalent 
National Standards. 
 
(a) adhesion testing in accordance with LSO 4624 using Method A or B as 
applicable. The coating shall exhibit an  adhesion rating of either 4A or 4B, 
as applicable; 
(b) flexibility in accordance with ASTM D522 Mandrel Bend Test of Attached 
Organic Coatings, using Test Method B with a 12.7 mm (0.5 in) mandrel at 
the specified thickness at -20 °C. Samples for the flexibility test shall be 
prepared in accordance with the ASTM  D522 standard. There shall not be 
any visually apparent cracks; 
(c) impact resistance in accordance with ASTM D2794 Test method for 
Resistance of Organic Coatings to the Effects of Rapid Deformation 
(Impact). The coating at room temperature shall pass a forward impact test 
of 18 J (160 in-lbs); 
(d) chemical resistance when tested in general accordance with ASTM D1308 
Effect of Household Chemicals on Cl ear and Pigmented Organic Finishes. 
The tests shall be conducted using th e Open Spot Test Method and 100 hour 
exposure to a 30 per cent sulfuric acid solution (battery acid with a specific 
gravity of 1.219) and 24 hour exposure to a polyalkalene glycol (e.g. brake fluid). There shall be no evidence of lifting, blistering or softening of the 
coating. The adhesion shall meet a rati ng of 3 when tested in accordance 
with ASTM D3359; 
(e) Minimum 1,000 hours exposure in accord ance with ASTM G53 Practice for 
Operating Light- and Water-Exposure Apparatus (Fluorescent W-Condensation Type) for Exposure of non- metallic Materials. There shall be 
no evidence of blistering, and adhesion sh all meet a rating of 3 when tested 
in accordance with ISO 4624. The maximum gloss loss allowed is 20 per cent; 
(f) minimum 500 hours exposure in accord ance with ASTM B117 Test Method GSO STANDARD                                                                     GSO  /    
 
 
 78of Salt Spray (Fog) Testing. Undercutting shall not exceed 3 mm at the scribe mark, there shall be no evid ence of blistering, and adhesion shall 
meet a rating of 3 when tested in accordance with ASTM D3359; 
(g) resistance to chipping at room  temperature using the ASTM D3170 
Chipping Resistance of Coatings. The co ating shall have a rating of 7A or 
better, and there shall not be any exposure of the substrate; 
 
A.9.2. Coating batch tests  
(a) Coating thickness   
The thickness of the coating shall meet the requirements of the design when tested in accordance with ISO 2808;   
 (b) Coating adhesion   
 
The coating adhesion strength shall be measured in accordance with ISO 4624, and shall have a minimum ra ting of 4 when measured using 
either Test Method A or B, as appropriate. 
 A.10. Leak test
   
 
 Type CNG-4 designs shall be leak test ed using the following procedure (or an 
acceptable alternative); 
 
(a) cylinders shall be thoroughly dried and pressurized to working pressure 
with dry air or nitrogen, and containing a detectable gas such as helium; 
(b) any leakage measured at any point that exceeds 0.004 standard cm3/h shall 
be cause for rejection. 
 A.11. Hydraulic test
 
  One of the following two options shall be used:    Option 1
: Water jacket test 
 
(a) The cylinder shall be hydrostatically tested to at least 1.5 times working 
pressure. In no case may the test pressu re exceed the auto-frettage pressure; 
(b) Pressure shall be maintained fo r a sufficiently long period (at least 30 
seconds) to ensure complete expansion. Any internal pressure applied after 
auto-frettage and previous to the hydr ostatic test shall not exceed 90 per 
cent of the hydrostatic test pressure . If the test pressure cannot be 
maintained due to failure of the test apparatus, it is permissible to repeat the 
test at a pressure increased by 700 kPa.  Not more than 2 such repeat rests 
are permitted; GSO STANDARD                                                                     GSO  /    
 
 
 79(c) The manufacturer shall define the a ppropriate limit of permanent volumetric 
expansion for the test pressure used, but in no case shall the permanent expansion exceed 5 per cent of the total volumetric expansion measured under the test pressure. For type CNG- 4 designs, the elastic  expansion shall 
be established by the manufacturer. Any cylinders not meeting the defined 
rejection limit shall be rejected and eith er destroyed or used for batch test 
purposes.  
 
Option 2
: Proof pressure test 
 
The hydrostatic pressure in the cylinde r shall be increased gradually and 
regularly until the test pressure, at least 1.5 times working pressure, is 
reached. The cylinder test pressure shall be held for a sufficiently long period (at least 30 seconds) to ascertain that there is no tendency for the pressure to decrease and that tightness is guaranteed; 
 
A.12. Hydrostatic pressure burst test
 
 
(a) The rate of pressurisation shall not exceed 1.4 MPa per second 
(200 psi/second) at pressures in exce ss of 80 per cent of the design burst 
pressure. If the rate of pressurisation at pressures in excess of 80 per cent of 
the design burst pressure exceeds 350 kPa/second (50 psi/second), then 
either the cylinder must be placed schematically between the pressure 
source and the pressure measurement de vice, or there must be a 5 second 
hold at the minimum design burst pressure; 
(b) The minimum required (calculated) burst  pressure shall be at least 45 MPa, 
and in no case less than the value necessary to meet the stress ratio 
requirements. Actual burst pressure sh all be recorded. Rupture may occur in 
either the cylindrical region or the dome region of the cylinder. 
 A.13. Ambient temperature pressure cycling
 
 
 Pressure cycling shall be performed in  accordance with the following procedure: 
 
(a) fill the cylinder to be te sted with a non-corrosive fluid such as oil, inhibited 
water or glycol;  
(b) cycle the pressure in the cylinder be tween not more than 2 MPa and not less 
than 26 MPa at a rate not to exceed 10 cycles per minute. 
 
The number of cycles to failure shall be reported, along with the location and 
description of the failure initiation. 
 A.14. Acid environment test
 
 
 On a finished cylinder the following test procedure should be applied: GSO STANDARD                                                                     GSO  /    
 
 
 80 
(a) exposing a 150 mm diameter area on the cylinder surface for 100 hours to a 
30 per cent sulfuric acid solution (batte ry acid with a specific gravity of 
1.219) while the cylinder is held at 26 MPa; 
(b) the cylinder shall then be burst in accordance with the procedure defined in 
paragraph A.12 above and provide a bur st pressure that exceeds 85 per cent 
of the minimum design burst pressure. 
 
A.15. Bonfire test  
 
A.15.1. General   The bonfire tests are designed to demonstr ate that finished cylinders complete 
with the fire protection system (cylinde r valve, pressure relief devices and/or 
integral thermal insulation) specified in  the design will not burst when tested 
under the specified fire conditions. Extrem e caution must be exercised during fire 
testing in the event that cylinder rupture occurs; 
 
A.15.2. Cylinder set-up   Cylinders shall be placed horizontally with the cylinder bottom approximately 
100 mm above the fire source; Metallic shielding shall be used to prev ent direct flame impingement on cylinder 
valves, fittings, and/or pressure relief devices. The metallic shielding shall not be in direct contact with the specified fire  protection system (pressure relief devices 
or cylinder valve). Any failure during the te st of a valve, fitting or tubing that is 
not part of the intended protection system for the design shall invalidate the result. 
 A.15.3. Fire source  
A uniform fire source of 1.65 m length sha ll provide direct flame impingement on 
the cylinder surface across its entire diameter.  Any fuel may be used for the fire source provided it supplies uniform heat 
sufficient to maintain the specified test temperatures until the cylinder is vented. The selection of fuel should take into consideration air pollution concerns. The arrangement of the fire shall be recorded in sufficient detail to ensure the rate of 
heat input to the cylinder is reproducible. Any failure or inconsistency of the fire 
source during a test invalidate the result; 
 A.15.4. Temperature and pressure measurements  
Surface temperatures shall be monitored by at least three thermocouples located along the bottom of the cylinder and spaced  not more than 0.75 m apart; Metallic 
shielding shall be used to prevent dir ect flame impingement on the thermocouples. GSO STANDARD                                                                     GSO  /    
 
 
 81Alternatively, thermocouples may be insert ed into blocks of metal measuring less 
than 25 mm square.  Thermocouple temperatures and the cylinder pressure shall be recorded at intervals of every 30 seconds or less during the test. 
 
A.15.5. General test requirements  
Cylinders shall be pressurized with na tural gas and tested in the horizontal 
position at both:  (a) working pressure; (b) 25 per cent of the working pressure. Immediately following ignition, the fire shall produce flame impingement on the 
surface of the cylinder along the 1.65 m lengt h of the fire source and across the 
cylinder diameter. Within 5 minutes of ignition, at least one thermocouple shall 
indicate a temperature of at least 590 °C. This minimum temperature shall be 
maintained for the remaining duration of the test. 
 
A.15.6. Cylinders 1.65 m length or less   The centre of the cylinder shall be positioned over the centre of the fire source;  A.15.7. Cylinders greater than 1.65 m length   If the cylinder is fitted with a pressure  relief device at one end, the fire source 
shall commence at the opposite end of the cy linder; If the cylinder is fitted with 
pressure relief devices at both ends, or at more than one location along the length 
of the cylinder, the centre of the fire s ource shall be centred midway between the 
pressure relief devices that are separated by the greatest horizontal distance. 
 
If the cylinder is additionally protected using thermal insulation, then two fire 
tests at service pressure shall be perf ormed, one with the fire centred midway 
along the cylinder length, and the other with  the fire commencing at one of the 
cylinder ends. 
 A.15.8. Acceptable results   The cylinder shall vent through a pressure relief device.  A.16. Penetration tests
 
 
 A cylinder pressurised to 20 MPa ± 1 MPa with compressed gas shall be 
penetrated by an armour piercing bullet with a diameter of 7.62 mm or greater. 
The bullet shall completely penetrate at least one side wall of the cylinder. For GSO STANDARD                                                                     GSO  /    
 
 
 82type CNG-2, CNG-3 and CNG-4 designs, the projectile shall impact the side wall 
at an approximate angle of 45 °. The cylinder shall reveal no evidence of 
fragmentation failure. Loss of small pieces  of material, each not weighing more 
than 45 grams, shall not constitute failure  of the test. The approximate size of 
entrance and exit openings and their locations shall be recorded. 
 
A.17. Composite flaw tolerance tests  
 
 For type CNG-2, CNG-3 and CNG-4 de signs only, one finished cylinder, 
complete with protective coating, shall have  flaws in the longit udinal direction cut 
into the composite. The flaws shall be great er than the visual inspection limits as 
specified by the manufacturer. 
 The flawed cylinder shall then be pressure cycled from not more than 2 MPa to 
not less than 26 MPa for 3,000 cycles, fo llowed by an additional 12,000 cycles at 
ambient temperature; The cylinder shall not  leak or rupture within the first 3,000 
cycles, but may fail by leakage during the last 12,000 cycles. All cylinders which 
complete this test shall be destroyed. 
 A.18. High temperature creep test
 
 
 This test is required for all type C NG-4 designs, and all type CNG-2 and CNG-3 
designs in which the glass transition te mperature of the resin matrix does not 
exceed the maximum design material te mperature given in paragraph 4.4.2. of 
Annex 2 by at least 20 °C. One finished cylinder shall be tested as follows: 
(a) The cylinder shall be pressurised to  26 MPa and held at a temperature of 
100 °C for not less than 200 hours;  
(b) Following the test, the cylinder shall meet the requirements of the 
hydrostatic expansion test A.11, the leak  test A.10, and the burst test A.12 
above. 
 
A.19. Accelerated stress rupture test  
 
 For type CNG-2, CNG-3, and CNG-4 desi gns only, one cylinder free of protective 
coating shall be hydrostatica lly pressurised to 26 MPa while immersed in water at 
65 °C. The cylinder shall be held at this  pressure and temperature for 1,000 hours. 
The cylinder shall then be pressured to  burst in accordance with the procedure 
defined in paragraph A.12 above except th at the burst pressure shall exceed 
85 per cent of the minimum design burst pressure; 
 
A.20. Impact damage test  
 
 One or more finished cylinders shall be drop tested at ambient temperature 
without internal pressurisation or attached valves. The surface onto which the cylinders are dropped shall be a smooth, hor izontal concrete pad or flooring. One 
cylinder shall be dropped in a horizontal  position with the bottom 1.8 m above the GSO STANDARD                                                                     GSO  /    
 
 
 83surface onto which it is dropped. One cylinde r shall be dropped vertically on each 
end at a sufficient height above the floor or pad so that the potential energy is 488 
J, but in no case shall the height of th e lower end be greater than 1.8 m. One 
cylinder shall be dropped at a 45 ° angle onto a dome from a height such that the 
centre of gravity is at 1.8 m; however, if the lower end is clos er to the ground than 
0.6 m, the drop angle shall be changed to maintain a minimum height of 0.6 m and 
a centre of gravity of 1.8 m. 
 
 Following the drop impact, the cylinders sh all be pressure cycled from not more 
than 2 MPa to not less than 26 MPa bar for 1,000 cycles times the specified service life in years. The cylinders may leak but not rupture, during the cycling. 
Any cylinders completing the cycling test shall be destroyed; 
 A.21. Permeation test
 
 
 This test is only required on type CNG- 4 designs. One finished cylinder shall be 
filled with compressed natural gas or a 90 per cent nitrogen/10 per cent helium mixture to working pressure, placed in an  enclosed sealed chamber at ambient 
temperature, and monitored for leakage fo r a time sufficient to establish a steady 
state permeation rate. The permeation rate shall be less than 0.25 ml of natural gas 
or helium per hour per litre water capacity of the cylinder. 
 
A.22. Tensile properties of plastics
 
 
 The tensile yield strength and ultimate elonga tion of plastic liner material shall be 
determined at -50 °C using ISO 3628, and meet the requirements of paragraph 
6.3.6. of Annex 2. 
 A.23. Melting temperature of plastics
 
  Polymeric materials from finished liner s shall be tested in accordance with the 
method described in ISO 306, and meet the requirements of paragraph 6.3.6. of 
Annex 2. 
 A.24. Pressure relief device requirements
 
 
Pressure relief device specified by the manufacturer shall be shown to be 
compatible with the service conditions listed in paragraph 4. of Annex 2 and through the following qualification tests:  (a) One specimen shall be held at a c ontrolled temperature of not less than 
95 °C and a pressure not less than test  pressure (30 MPa) for 24 hours.  At 
the end of this test there shall be no leakage or visible sign of extrusion of 
any fusible metal used in the design. 
(b) One specimen shall be fatigue tested at  a pressure cycling rate not to exceed GSO STANDARD                                                                     GSO  /    
 
 
 844 cycles per minute as follows: 
(i) held at 82 °C while pressured for 10,000 cycles between 2 MPa and 
26 MPa; 
(ii) held at -40 °C while pressure for 10,000 cycles between 2 MPa and 
20 MPa. 
At the end of this test there shall be no leakage, or any visible sign of 
extrusion of any fusible metal used in the design. 
(c) Exposed brass pressure retaining com ponents of pressure relief devices shall 
withstand, without stress corrosion crack ing, a mercurous nitrate test as 
described in ASTM B154. The pressure relief device shall be immersed for 
30 minutes in an aqueous mercurous nitrate solution containing 10 g of 
mercurous nitrate and 10 ml of nitric acid per litre of solution. Following the immersion, the pressure relief device shall be leak test ed by applying an 
aerostatic pressure of 26 MPa for one minute during which time the component shall be checked for extern al leakage; Any leakage shall not 
exceed 200 cm
3/h; 
(d) Exposed stainless steel pressure re taining components of pressure relief 
devices shall be made of an alloy type  resistant to chloride induced stress 
corrosion cracking; 
 
A.25. Boss torque test  
 
The body of the cylinder shall be restrain ed against rotation and a torque of 500 
Nm shall be applied to each end boss of the cylinder, first in the direction to 
tighten a threaded connection, then in the untightening direction, and finally again in the tightening direction. 
 
A.26. Resin shear strength
 
 
 Resin materials shall be tested on a sample coupon representative of the 
composite over-wrap in accordance with AS TM D2344, or an equivalent National 
Standard. Following a 24-hour water boil the composite shall have a minimum 
shear strength of 13.8 MPa. 
 
A.27. Natural gas cycling test  
 
 One finished cylinder shall be pressure cycled using compressed natural gas from 
less than 2 MPa to working pressure for 300 cycles. Each cycle, consisting of the filling and venting of the cylinder, sha ll not exceed 1 hour. The cylinder shall be 
leak tested in accordance with paragra ph A.10 above and meet the requirements 
therein. Following the completion of the natural gas cycling the cylinder shall be 
sectioned and the liner/end boss inte rface inspected for evidence of any 
deterioration, such as fatigue cracking or electrostatic discharge. 
 
 NOTE
 - Special consideration must be give n to safety when conducting this test. GSO STANDARD                                                                     GSO  /    
 
 
 85Prior to conducting this test, cylinders of  this design must have successfully 
passed the test requirements of paragra ph A.12 above (hydrostatic pressure burst 
test), paragraph 8.6.3. of A nnex 2 (ambient temperature pressure cycling test) and 
paragraph A.21 above (permeation test). Pr ior to conducting this test, the specific 
cylinders to be tested must pass the te st requirements of paragraph A.10 above 
(leak test). 
 
A.28. Manual valve device requirements  
 
 One specimen shall be submitted to a fatigue test at a pressure cycling rate not to 
exceed 4 cycles per minute as follows: 
  (a) held at 20 °C while pressured fo r 2000 cycles between 2 MPa and 26 MPa. 
 
A.29. Bend test, welded stainless steel liners
 
 
 Bend tests shall be carried out on material  taken from the cylindrical part of a 
welded stainless steel liner and tested in accordance with the method described in 
paragraph 8.5. of EN 13322-2.  The test pi ece shall not crack when bent inwards 
around a former until the inside edges are not  further apart than the diameter of 
the former. 
 GSO STANDARD                                                                     GSO  /    
 
 
  
Annex 2 - Appendix B
 
 
REPORT FORMS 
 
NOTE  - This appendix is not a mandatory part of this annex. 
 The following forms should be used:  
(1) Report of Manufacture & Certificate of C onformance - Required to be clear, legible 
and in the format of Form 1. 
(2) Report 1
/ of Chemical Analysis of Material fo r Metallic Cylinders, Liners, or Bosses - 
Required essential elements, identification, etc. 
(3) Report 1 / of Mechanical Properties of Material for Metallic Cylinders and Liners - 
Required to report all tests required by this Regulation. 
(4) Report 1 / of Physical and Mechanical Properties of Materials for Non Metallic Liners - 
Required to report all tests and information required in this Regulation.  
(5) Report 1 / of Composite Analysis - Required to re port all tests and data required in this 
Regulation.  
(6) Report of Hydrostatic Tests, Periodic Pre ssure Cycling and Burst Tests - Required to 
report test and data required in this Regulation. 
 Form 1: Report of Manufacturer and Certification of Conformance
 
 Manufactured by:  Located at:  Regulatory Registration Number: 
 
Manufacturers Mark and Number:  Serial Number: from ..........................................to ............................................ inclusive  Cylinder description:  SIZE: Outside diameter: ..............................mm;  Length: .........................................mm;  Marks stamped on shoulder or on labels of the cyclinder are: 
 
(a) "CNG only": ................................................................................................................ ..  
                    
 
1/ Report forms 2 through 6 shall be developed by the manufacturer and must fully identify 
cylinders and requirements. Each report shall be signed by the Competent Authority and the 
manufacturer. GSO STANDARD                                                                     GSO  /    
 
 
 87(b) "DO NOT USE AFTER": .............................................................................................  (c) "Manufacturer's mark":..................................................................................................  (d) Serial and part number: .................................................................................................  (e) Working pressure in MPa:.............................................................................................   (f) ECE Regulation: ............................................................................................................  
(g) Fire prot ection type: ......................................................................................................  
(h) Date of original test (month & year): ............................................................................  
(i) Tare mass of empt y cylinder (in kg): .............................................................................  
(j) Authorized Body or  Inspectors Mark:............................................................................  
(k) Water capac ity in L: ......................................................................................................  
(l) Test pressu re in MPa:.....................................................................................................  
(m) Any special instructions: ..............................................................................................  
 
Each cylinder was made in compliance with all requirements of ECE Regulation No. ... in 
accordance with the cylinder description above. Required reports of test results are attached. I hereby certify that all these test results proved satisfactory in every way and are in compliance 
with the requirements for the type listed above.  
Comments: ...................................................................................................................... ....  
 Competent Authority: ........................................................................................................   Inspector’s signature: ......................................................................................................... . 
Manufacturer's signature:....................................................................................................   Place, Date: ................................................................................................................... ......  
  GSO STANDARD                                                                     GSO  /    
 
 
Annex 2 - Appendix C  
 
VERIFICATION OF STRESS RATIOS USING STRAIN GAUGES 
 1. The stress-strain relationship for fibres is always elastic, therefore, stress ratios 
and strain ratios are equal. 
 
2. High elongation strain gauges are required. 
 3. Strain gauges should be orientated in the direction of the fibres on which they are 
mounted (i.e. with hoop fibre on the outside  of the cylinder, mount gauges in the 
hoop direction). 
 4. Method 1 (applies to cylinders that do not use high tension winding)
 
 
(a) Prior to auto-frettage, apply strain gauges and calibrate; 
(b) Measure strains at auto-frettage, zero after auto-frettage, working, and 
minimum burst pressure have been met;   
(c) Confirm that the strain at burst pressure divided by strain at working 
pressure meets the stress ratio requirements. For hybrid construction, the 
strain at working pressure, is compared  with the rupture strain of cylinders 
reinforced with a single fibre type. 
 
5. Method 2 (applies to all cylinders)  
 
(a) At zero pressure after winding and auto-frettage, apply strain gauges and 
calibrate; 
(b) Measure strains at zero, working, and minimum burst pressure;  
(c) At zero pressure, after strain measurements have been taken at the working 
and minimum burst pressures, and w ith strain gauges monitored, cut the 
cylinder section apart so that the re gion containing the strain gauge is 
approximately five inches long. Rem ove the liner without damaging the 
composite. Measure the strains after the liner is removed. 
(d) Adjust the strain readings at zer o, working, and minimu m burst pressures by 
the amount of strain measured at zero pressure with and without the liner. 
(e) Confirm that the strain at burst pressure divided by strain at working 
pressure meets the stress ratio requirements. For hybrid construction, the 
strain at working pressure is compared with the rupture strain of cylinders reinforced with a single fibre type. 
  GSO STANDARD                                                                     GSO  /    
 
 
Annex 2 - Appendix D  
 
FRACTURE PERFORMANCE METHODS 
 F.1. Determination of fatigue sensitive sites
 
  The location and orientation of fatigue failure in cylinders shall be determined by 
appropriate stress analysis or by full scal e fatigue tests on finished cylinders as 
required under the design qualification tests for each type of design. If finite 
element stress analysis is used, the fatigue sensitive site shall be identified based on the location and orientatio n of the highest tensile principal stress concentration 
in the cylinder wall or liner at the working pressure. 
 
F.2. Leak-Before-Break (LBB)
 
 
F.2.1. Engineering critical assessment  This anal ysis may be carried out to establish that 
the finished cylinder will leak in the even t of a defect in the cylinder or liner 
growing into a through-wall crack. A leak-before-break assessment shall be performed at the cylinder side wall. If th e fatigue sensitive location is outside the 
side wall, a leak-before-break assessment sh all also be performed at that location 
using a Level II approach as outlined in BS PD6493. The assessment shall include 
the following steps: 
 
(a) Measure the maximum length (i.e. major axis) of the resultant through-wall 
surface crack (usually elliptical in sh ape) from the three cylinder cycle 
tested under the design qualification te sts (according to paragraphs A.13 
and A.14 of Appendix A) for each type  of design. Use the longest crack 
length of the three cylinders in the analysis. Model a semi-elliptical through-wall crack with a major axis e qual to twice the measured longest 
major axis and with a minor axis e qual to 0.9 of wall thickness. The semi-
elliptical crack shall be modelled at the locations specified in paragraph F.1. of Appendix D. The crack shall be oriented such that the highest tensile principal stress shall drive the crack;  
(b) Stress levels in the wall/liner at 26 MP a obtained from the stress analysis as 
outlined in paragraph 6.6 of Annex 2 shall be used for the assessment. Appropriate crack driving forces shall be calculated using either Section 9.2 or 9.3 of BS PD6493;  
(c) Fracture toughness of the finished cy linder or the liner from a finished 
cylinder, as determined at room temperature for aluminium and at -40 °C 
for steel, shall be established using a standardized testing technique (either ISO/DIS 12737 or ASTM 813-89 or BS 7448) in accordance with 
Sections 8.4 and 8.5 of BS PD6493;  
(d) Plastic collapse ratio shall be calcu lated in accordance with Section 9.4 of 
BS PD6493-91;  
(e) The modelled flaw shall be acceptable in accordance with Section 11.2 of 
BS PD6493-91. 
 F.2.2. LBB by flawed cylinder burst GSO STANDARD                                                                     GSO  /    
GSO STANDARD                                                                     GSO  /    
 
 
 90 
A fracture test shall be perf ormed by the cylinder side wall. If the fatigue sensitive 
locations as determined in paragraph F .1. (Appendix D) is outside the side wall, 
the fracture test shall also be performed at that location. The test procedure is as follows: 
 
(a) Determination of leak-before-break flaw length 
  The length of the LBB flaw at the fa tigue sensitive site shall be twice the 
length of the maximum length measured of the resultant through-wall surface crack from the three cylinders  cycle tested to failure under the 
design qualification tests for each type of design; 
 (b) Cylinder flaws    For type CNG-1 designs having fatigue sensitive site in the cylindrical part 
in the axial direction, external flaw s shall be machined longitudinally, 
approximately at mid-length of the cy lindrical part of the cylinder. The 
flaws shall be located at minimum wa ll thickness of the midsection based on 
thickness measurements at four points around the cylinder. For type CNG-1 designs having fatigue sensitive site out side the cylindrical part, the LBB 
flaw shall be introduced at the inte rnal surface of the cylinder along the 
fatigue sensitive orientation. For type  CNG-2 and CNG-3 designs the LBB 
flaw shall be introduced in the metal liner; 
 
For flaws to be tested by monotonic pressure, the flaw cutter shall be 
approximately 12.5 mm thick with an angle of 45 °C and a tip radius of 
0.25 mm maximum. The cutter diameter shall be 50 mm for cylinder with 
outside diameter less than 140 mm, and 65 to 80 mm for cylinders with outside diameter greater than 140 mm (A standard CVN cutter is 
recommended). 
 
NOTE
 - The cutter should be sharpened regularly to assure tip radius meets 
specification. 
 The depth of the flaw may be adjusted to obtain a leak by monotonic hydro-pressurization. The crack shall not propagate by more than 10 per cent 
outside of the machined flaw measured on the external surface: 
(c) Test procedure   
 
The test shall be performed by monotonic pressurisation or cyclic 
pressurisation as described below:  (i) Monotonic pressurisation to burst GSO STANDARD                                                                     GSO  /    
 
 
 91  The cylinder shall be pressurised hydrostatically until pressure is 
released from the cylinder at th e flaw location. The pressurisation 
shall be performed as described in paragraph A.12. (Appendix A); 
 
(ii) Cyclic pressure   The test procedure shall be in accordance with the requirements of 
paragraph A.13. of Appendix A.  
 (d) Acceptance criteria for the flawed cylinder test  
 
The cylinder passes the tests if the following conditions are met: 
 
(i) For monotonic pressurisation burst test, the failed pressure shall be 
equal or greater than 26 MPa; 
 For monotonic pressurised burst test, a total crack length measured on 
the external surface of 1.1 times th e original machined length is 
allowed. 
(ii) For cycle tested cylinders, fati gue crack growth beyond the original 
machined flaw length is allowed. However, the failure mode must be a "leak". Propagation of the flaw by fatigue should occur over at least 90 per cent of the length of the original machined flaw; 
 
NOTE
 - If these requirements are not fulfille d (failure occurs below 36 MPa, even 
and if the failure is a leak), a new test  can be performed with a less deep flaw. 
Also, if rupture type failure occurs at a pressure greater than 26 MPa and flaw 
depth is shallow, a new test can be performed with a deeper flaw. 
 
F.3. Defect size for non-destructive examination (NDE)  
 F.3.1. NDE Defect size by engineering critical assessment   Calculations shall be performed in accordance with British Standard (BS) PD 
6493, Section 3, using the following steps: (a) Fatigue cracks shall be modelled at the high stress location in the wall/liner 
as planar flaws;  
(b) The applied stress range at the fatigue sensitive site, due to a pressure 
between 2 MPa and 20 MPa, shall be es tablished from the stress analysis as 
outlined in paragraph F.1. of Appendix D;  
(c) The bending and membrane stress component may be used separately; 
(d) The minimum number of pressure cycles is 15,000; (e) The fatigue crack propagation data shall be determined in air in accordance 
with ASTM E647. The crack plane orientation shall be in the C-L direction (i.e., crack plane perpendicular to the circumferences and along the axis of GSO STANDARD                                                                     GSO  /    
GSO STANDARD                                                                     GSO  /    
 
 
 92the cylinder), as illustrated in ASTM E 399. The rate shall be determined as 
an average of 3 specimen tests. Wh ere specific fatigue crack propagation 
data are available for the material a nd service condition, they may be used 
in the assessment. 
(f) The amount of crack growth in th e thickness direction and in the length 
direction per pressures cycle shall be determined in accordance with the 
steps outlined in Section 14.2 of the BS PD 6493-91 standard by integrating the relationship between the rate of fa tigue crack propagation, as established 
in e) above, and the range of crack driving force corresponding to the applied pressure cycle;  
(g) Using the above steps, calculate th e maximum allowable defect depth and 
length which shall not cause  the failure of the cylinder during the design life 
due to either fatigue or rupture. The defect size for NDE shall be equal to or less than the calculated maximum allowable defect size for the design. 
 F.3.2. NDE Defect size by flawed cylinder cycling  
For type CNG-1, CNG-2 and CNG-3 designs , three cylinders containing artificial 
defects that exceed the defect length and depth detection capability of the NDE inspection method required in paragra ph 6.15. of Annex 2, shall be pressure 
cycled to failure in accordance with th e test method in pa ragraph A.13 (Appendix 
A). For type CNG-1 designs having a fatigue sensitive site in the cylindrical part, 
external flaws shall be introduced on th e side wall. For type CNG-1 designs 
having the fatigue sensitive site outside the side wall, and for type CNG-2 and 
CNG-3 designs, internal flaws shall be  introduced. Internal flaws may be 
machined prior to the heat treating and closing of the end of the cylinder. 
 
The cylinders shall not leak or ruptur e in less than 15,000 cycles; The allowable 
defect size for NDE shall be equal to or less than the artificial flaw size at that 
location. GSO STANDARD                                                                     GSO  /    
 
 
Annex 2 - Appendix E  
 
INSTRUCTIONS BY THE CONTAI NER MANUFACTURER REGARDING 
HANDLING, 
USE AND INSPECTION OF CYLINDERS 
 G.1. General
 
  The primary function of this appendix is to provide guidance to the cylinder 
purchaser, distributor, installer and user for the safe use of the cylinder over its 
intended service life. 
 G.2. Distribution
 
 
The manufacturer shall advise the purchaser that the instructions shall be supplied 
to all parties involved in the distribu tion, handling, installation and use of the 
cylinders; The document may be reproduced to provide sufficient copies for this purpose, however it shall be marked to pr ovide reference to the cylinders being 
delivered; 
  
G.3. Reference to existing codes, standards and regulations
 
 
Specific instructions may be stated by re ference to national or recognised codes, 
standards and regulations. 
 
G.4. Cylinder handling  
 
Handling procedures shall be provided to ensure that the cylinders will not suffer 
unacceptable damage or contamination during handling. 
 G.5. Installation
 
 
Installation instructions shall be provide d to ensure that the cylinders will not 
suffer unacceptable damage during insta llation and during normal operation over 
the intended service life.  Where the mounting is specified by the manufacturer, the instructions shall 
contain where relevant, details such as mounting design, the use of resilient gasket 
materials, the correct tightening torques and avoidance of direct exposure of the 
cylinder to an environment of chemical and mechanical contacts.  Where the mounting is not specified by the manufacturer, the manufacturer shall 
draw the purchaser's attention to possible long term impacts of the vehicle mounting system, for example: ve hicle body movements and cylinder 
expansion/contraction in the pressure and temperature conditions of service.  Where applicable, the purchaser's attention shall be drawn to the need to provide installations such that liquids or solid s cannot be collected to cause cylinder GSO STANDARD                                                                     GSO  /    
GSO STANDARD                                                                     GSO  /    
 
 
 94material damage;  The correct pressure relieve device to be fitted shall be specified. 
 G.6. Use of cylinders
 
 
The manufacturer shall draw the purchaser 's attention to the intended service 
conditions specified by this Regulation, in  particular the cylinder's allowable 
number of pressure cycles. its  life in years, the gas quality limits and the allowable 
maximum pressures. 
 
G.7. In-service inspection  
 
The manufacturer shall clearly specify the user's obligation to observe the 
required cylinder inspection requirements (e.g. reinspection interval, by 
authorised personnel). This information shall be in agreement with the design 
approval requirements. 
 
 GSO STANDARD                                                                     GSO  /    
 
 
Annex 2 - Appendix F  
 
ENVIRONMENTAL TEST 
 H.1. Scope
 
 
The environmental test is intended to  demonstrate that NGV cylinders can 
withstand exposure to the automotive underbody environment and occasional exposure to other fluids. This test wa s developed by the US automotive industry 
in response to cylinder failures initia ted by stress corrosion cracking of the 
composite wrap. 
 
H.2. Summary of test method
 
 
A cylinder is first preconditioned by a combination of pendulum and gravel 
impacts to simulate potential underbody cond itions. The cylinder is then subjected 
to a sequence of immersion in simulate d road salt/acid rain, exposure to other 
fluids, pressure cycles and high and low temperature exposures. At the conclusion 
of the test sequence the cylinder will be  hydraulically pressured to destruction. 
The remaining residual burst strength of th e cylinder shall be not less than 85 per 
cent of the minimum design burst strength. 
 
H.3. Cylinder set-up and preparation  
 
The cylinder shall be tested in a conditi on representative of installed geometry 
including coating (if applicable), brackets and gaskets, and pressure fittings using 
the same sealing configuration (i.e. O-rings ) as that used in service. Brackets may 
be painted or coated prior to installation in the immersion test if they are painted 
or coated prior to vehicle installation. 
 
Cylinders will be tested horizontally a nd nominally divided along their horizontal 
centreline into "upper" and "lower" sec tions. The lower section of the cylinder 
will be alternatively immersed in road sa lt/acid rain environment and in heated or 
cooled air.  The upper section will be divided into 5 distinct areas and marked for preconditioning and fluid exposure. The areas will be nominally 100 mm in diameter. The areas shall not overlap on the cylinder surface. While convenient 
for testing, the areas need not be oriented  along a single line, but  must not overlap 
the immersed section of the cylinder.  Although preconditioning and fluid exposur e is performed on the cylindrical 
section of the cylinder, all of the cylinder, including the domed sections, should be as resistant to the exposure environments as are the exposed areas. 
 
Other fluid 
exposure areas 
 GSO STANDARD                                                                     GSO  /    
 
 
 96
       
 
Immersion area 
(lower third) 
 
Figure H.1
 - Cylinder orientation and layout of exposure areas 
 
H.4. Preconditioning apparatus  
  The following apparatus are needed for preconditioning the test cylinder by 
pendulum and gravel impact. 
 
(a) Pendulum impact 
 
The impact body shall be of steel and have the shape of a pyramid with 
equilateral triangle faces and a square base, the summit and the edges being 
rounded to a radius of 3 mm. The centre of percussion of the pendulum shall 
coincide with the centre of gravity of  the pyramid;  its distance from the 
axis of rotation of the pendulum sh all be 1 m. The total mass of the 
pendulum referred to its centre of percussion shall be 15 kg. The energy of the pendulum at the moment of impact shall be not less than 30 Nm and as 
close to that value as possible.  During pendulum impact, the cylinder sh all be held in position by the end 
bosses or by the intended mounting brackets. 
 (b) Gravel impact  
Machine constructed according to the design specifications shown in figure 
H.2.This procedure for operation of the equipment shall follow that 
described in ASTM D3170, Standard Te st Method for Chip Resistance of 
Coatings with the exception that the cylinder may be at ambient temperature during gravel impact; 
 (c) Gravel  
Alluvial road gravel passing through a 16 mm space screen but retained on a 9.5 mm space screen. Each application is  to consist of 550 ml of graded 
gravel (approx. 250 to 300 stones). GSO STANDARD                                                                     GSO  /    
 
 
 97
        
 
        
      
Figure H.2
 - Gravel impact test 
 
H.5. Exposure environments  
 (a) Immersion environment  
At the specified stage in the test sequence (table 1) the cylinder will be oriented horizontally with the lower third of the cylinder diameter immersed in a simulated acid rain/road salt wate r solution. The solution will consist of 
the following compounds: 
 
Deionized water;  
Sodium chloride: 2.5 per cent by weight ± 0.1 per cent; Calcium chloride: 2.5 per cent by weight ± 0.1 per cent;  Sulfuric acid: Sufficient to achieve a solution pH of 4.0 ± 0.2;   
 
Solution level and pH are to be adjusted  prior to each test step which uses 
this liquid.  
The temperature of the bath shall be 21 ± 5 °C. During immersion, the 
unsubmerged section of the cylinder shall be in ambient air. 
 
(b) Other fluid exposure GSO STANDARD                                                                     GSO  /    
 
 
 98 
At the appropriate stage in test sequence (table 1) each marked area is to be exposed to one of five solutions for 30 minutes. The same environment shall 
be used for each location throughout the test. The solutions are: 
 
Sulfuric acid: 19 per cent solution by volume in water; 
Sodium hydroxide: 25 per cent solution by weight in water;  Methanol/gasoline: 30/70 per cent concentrations;  Ammonium nitrate: 28 per cent by weight in water;  Windshield washer fluid. 
 
When exposed, the test sample will be oriented with the exposure area uppermost. A pad of glass wool one layer thick (approximately 0.5 mm) and trimmed to the appropriate dimensions is to be placed on the exposure area. 
Using a pipet, apply 5 ml of the test fluid to the exposure area. Remove the gauze pad after pressurization of the cylinder for 30 minutes. 
 H.6. Test conditions
 
 
(a) Pressure cycle 
 
As defined in the test sequence, cy linder shall be hydraulically pressure 
cycled between not more than 2 MPa and not less than 26 MPa. The total 
cycle shall be not less than 66 seconds and will include a 60 second 
minimum hold at 26 MPa. The nominal cycle process will be: 
 
Ramp up from ≤ 20 MPa to ≥ 26 MPa;  
Hold at ≥ 26 MPa for 60 seconds minimum; 
Ramp down from ≥ 26 MPa to ≤ 2 MPa;  
Total minimum cycle time to be 66 seconds. 
(b) Pressure during other fluid exposure  
Following application of the other fluids, the cylinder shall be pressured to not less than 26 MPa for a minimum of 30 minutes; 
 (c) High and low temperature exposure  
As defined in the test sequence, the entire cylinder shall be exposed to high 
or low temperature air in contact with external surface. The low temperature 
air shall be -40 °C or lower and the high temperature air shall be 
82 °C ± 5 °C. For the low temperature exposure, the fluid temperature of 
type CNG-1 cylinders shall be mon itored using a thermocouple installed 
within the cylinder to ensure it remains at -40 °C or lower. 
 
H.7. Test procedure
 GSO STANDARD                                                                     GSO  /    
 
 
 99 
(a) Preconditioning of the cylinder  
Each of the five areas marked for ot her fluid exposure an the upper section 
of the cylinder shall be preconditione d by a single impact of the pendulum 
body summit at their geometric centre. Following impact, the five areas 
shall be further conditioned by a gravel impact application.  The central section of the bottom por tion of the cylinder that will be 
submerged shall be preconditioned by an impact of the pendulum body 
summit at three locations spaced approximately 150 mm apart.  Following impact, the same central s ection that was impacted shall be 
further conditioned by a gravel impact application.  The cylinder shall be unpressured during preconditioning.  
 (b) Test sequence and cycles  
The sequence of the environment exposure, pressure cycles, and 
temperature to be used are defined in table 1.  The cylinder surface is not to be washed or wiped between stages.  
H.8. Acceptable results
 
 
Following the above test sequence, the cylinder shall be hydraulically tested to 
destruction in accordance with the pr ocedure in paragraph A.12. The burst 
pressure of the cylinder shall be not le ss than 85 per cent of the minimum design 
burst pressure. 
 
Table H.1  - Test conditions and sequence 
 
Test steps Exposure 
environments Number of 
pressure 
cycles Temperature 
1 Other fluids -- Ambient 
2 Immersion 1875 Ambient 
3 Air 1875 High 
4 Other fluids -- Ambient 
5 Immersion 1875 Ambient 
6 Air 3750 Low 
7 Other fluids -- Ambient 
8 Immersion 1875 Ambient 
9 Air 1875 High 
10 Other fluids -- Ambient GSO STANDARD                                                                     GSO  /    
 
 
 10011 Immersion 1875 Ambient 
 GSO STANDARD                                                                     GSO  /    
 
 
Annex 4A  
 
PROVISIONS REGARDING THE APPROVAL OF THE AUTOMATIC VALVE, NON-
RETURN VALVE, THE PRESSURE RELIEF VALVE, PRESSURE RELIEF DEVICE 
AND THE EXCESS FLOW VALVE 
 
1. The purpose of this annex is to determin e the provisions regarding the approval of 
the automatic valve, the non-return valve, the pressure relief valve, the pressure 
relief device and the excess flow valve. 
 2. The automatic valve
 
 
2.1. The materials constituting the automatic va lve which are in contact with the CNG 
when operating, shall be compatible with th e test CNG.  In order to verify this 
compatibility the procedure described in Annex 3D shall be used. 
 2.2. Operating specifications 
 
2.2.1. The automatic valve shall be so designed as to withstand a pressure of 1.5 times 
the working pressure (MPa) without leakage and deformation. 
 2.2.2. The automatic valve shall be so designe d as to be leak-proof at a pressure 
of 1.5 times the working pressure (MPa) (see Annex 3B). 
 2.2.3. The automatic valve, being in the normal position of use specified by the 
manufacturer, is submitted to 20,000 operations;  then it is deactivated.  The automatic valve shall remain leak-proof at a pressure of 1.5 times the working 
pressure (MPa) (see Annex 3B). 
 2.2.4. The automatic valve shall be so designed to operate at temperatures as specified in 
Annex 3O.  
 2.3. The electrical system, if existing, shall be isolated from the body of the automatic 
valve.  Isolation resistance shall be > 10 M Ω. 
 2.4. The automatic valve activated  by an electric current shall be in a "closed" position 
when the current is switched off. 
 2.5. The automatic valve has to comply w ith the test procedures for the Class 
component determined according to the sc heme in Figure 1-1 of paragraph 2 of 
this Regulation. 
 3. The non-return valve
 
 
3.1. The materials constituting the non-return va lve which are in contact with the CNG 
when operating, shall be compatible with th e test CNG.  In order to verify this 
compatibility the procedure described in Annex 3D shall be used. 
 3.2. Operating specifications GSO STANDARD                                                                     GSO  /    
 
 
 102 3.2.1. The non-return valve shall be so designed as to withstand a pressure of 1.5 times 
the working pressure (MPa) without leakage and deformation. 
 3.2.2. The non-return valve shall be so designed as to be leak-proof (external) at a 
pressure of 1.5 times the working pressure (MPa) (see Annex 3B). 
 
3.2.3. The non-return valve, being in the normal position of use specified by the 
manufacturer, is submitted to 20,000 operati ons; then it is deactivated.  The non-
return valve shall remain leak-proof (e xternal) at a pressure of 1.5 times the 
working pressure (MPa) (see Annex 3B). 
 3.2.4. The non-return valve shall be so designed to operate at temperatures as specified 
in Annex 3O. 
 3.3. The non-return valve has to comply with the test procedures for the Class 
component determined according to the scheme in Figure 1-1 of paragraph 2 of this Regulation. 
 4. The pressure relief valve and pressure relief device
 
 
4.1. The materials constituting the pressure relief valve and pressure relief device 
which are in contact with the CNG when operating, shall be compatible with the 
test CNG.  In order to verify this compatibility, the procedure described in Annex 3D shall be used. 
 
4.2. Operating specifications 
 4.2.1. The pressure relief valve and pressure relie f device in Class 0 shall be so designed 
as to withstand a pressure of 1.5 times the working pressure (MPa). 
 4.2.2. The pressure relief valve and pressure re lief device of Class 1 shall be so designed 
as to be leak-proof at a pressure of 1.5 times the working pressure (MPa) with the 
outlet closed off (see Annex 3B). 
 4.2.3. The pressure relief valve of Class 1 and Class 2 shall be so designed as to be leak-
proof at twice the working pressure with the outlets closed off. 
 4.2.4. The pressure relief device sh all be so designed to open the fuse at a temperature of 
110 ± 10 °C. 
 4.2.5. The pressure relief valve of Class 0 shall be so designed to operate at temperatures 
from -40 °C to 85 °C.  
 4.3. The pressure relief valve and pressure relief device have to comply with the test GSO STANDARD                                                                     GSO  /    
 
 
 103procedures for the Class component determined according to the scheme in    Figure 1-1 of paragraph 2 of this Regulation. 
 5. The excess flow valve
 
 5.1. The materials constituting the excess flow  valve which are in contact with the 
CNG when operating, shall be compatible with  the test CNG.  In  order to verify 
this compatibility, the procedure described in Annex 3D shall be used. 
 5.2. Operating specifications 
 
5.2.1. The excess flow valve, if it is not integr ated in the cylinder, shall be so designed 
as to withstand a pressure of 1.5 times the working pressure (MPa). 
 5.2.2. The excess flow valve shall be so designed as to be leak-proof at a pressure of 
1.5 times the working pressure (MPa). 
 5.2.3. The excess flow valve shall be so designed to operate at temper atures as specified 
in Annex 3O. 
 5.3. The excess flow valve shall be mounted inside the container.  5.4. The excess flow valve shall be designed with a bypass to allow for equalization of 
pressures. 
 5.5. The excess flow valve shall cut-off at a pressure difference over the valve of 650 
kPa. 
 5.6. When the excess flow valve is at cu t-off position, the by-pass flow through the 
valve shall not exceed 0.05 normal m
3/min at a differential pressure of 10,000 
kPa. 
 
5.7. The device have to comply with the te st procedures for the Class components, 
specified in the scheme in Figure 1-1 of  paragraph 2 of this Regulation, except 
overpressure, external leakage, resistance to dry heat test, ozone ageing. 
 
6. The manual valve  
 
6.1. The manual valve device in Class 0 shall be designed to withstand a pressure of 
1.5 times the working pressure. 
 6.2. The manual valve device in Class 0 shall be designed to operate at a temperature 
from -40 °C to 85 °C. 
 GSO STANDARD                                                                     GSO  /    
 
 
 104Annex 4B  
 
PROVISIONS REGARDING THE APPROVAL OF FLEXIBLE FUEL LINES OR HOSES 
 
Scope  
 The purpose of this annex is to determine the provisions regarding the approval of flexible hoses for use with CNG.  This annex covers three types of flexible hoses:  
(a) High pressure hoses (Class 0), 
(b) Medium pressure hoses (Class 1), (c) Low pressure hoses (Class 2) 
 1. HIGH PRESSURE HOSES, CLASS 0 CLASSIFICATION  1.1. General specifications  1.1.1. The hose shall be so designed as to withstand a maximum working pressure of 
1.5 times the working pressure (MPa). 
 1.1.2. The hose shall be so designed as to with stand temperatures as specified in Annex 
3O. 
 1.1.3. The inside diameter shall be in compliance with table 1 of Standard ISO 1307.  1.2. Hose construction  1.2.1. The hose must embody a smooth-bore tube  and a cover of suitable synthetic 
material, reinforced with one or more interlayer(s). 
 1.2.2. The reinforcing interlayer(s) has (have) to be protected by a cover against 
corrosion. 
  If for the reinforcing interlayer(s) co rrosion-resistant-material is used (i.e. 
stainless-steel) a cover is not required. 
 1.2.3. The lining and the cover must be smoot h and free from pores, holes and strange 
elements. 
 An intentionally provided puncture in th e cover shall not be considered as an 
imperfection. 
 1.2.4. The cover has to be intentionally perforated to avoid the forming of bubbles.  GSO STANDARD                                                                     GSO  /    
 
 
 1051.2.5. When the cover is punctured and the interlayer is made of a non-corrosion-
resistant material, the interlayer has to be protected against corrosion. 
 1.3. Specifications and tests for the lining  
1.3.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) 
 1.3.1.1. Tensile strength a nd elongation at break
 according to ISO 37. Tensile strength not 
less than 20 MPa and elongation at break not less than 250 per cent. 
 
1.3.1.2. Resistance to n-pentane  according to ISO 1817 with the following conditions: 
 
(a) medium: n-pentane 
(b) temperature: 23 °C (tolerance according to ISO 1817) 
(c) immersion period: 72 hours 
 
Requirements:  
 (a) maximum change in volume 20 per cent (b) maximum change in tensile strength 25 per cent (c) maximum change in elongation at break 30 per cent 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 1.3.1.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temperature = maximum operating temperature 
minus 10 °C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 1.3.1.1.  Requirements:  (a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 1.3.2. Tensile strength and elongation specific for thermoplastic material.  GSO STANDARD                                                                     GSO  /    
 
 
 1061.3.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. (b) tensile speed: 20 mm/min. 
 
The material has to be conditioned for at least 21 days at 23 °C and 50 per cent 
relative humidity prior to testing. 
 
Requirements: 
 
(a) tensile strength not less than 20 MPa. (b) elongation at break not less than 100 per cent. 
 
1.3.2.2. Resistance to n-pentane according to ISO 1817 with the following conditions:  
(a) medium: n-pentane. (b) temperature: 23 °C (tolerance according to ISO 1817). (c) immersion period: 72 hours.  Requirements:  (a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 1.3.2.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10  °C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 1.3.2.1.  Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. GSO STANDARD                                                                     GSO  /    
 
 
 107 1.4. Specifications and test-method for the cover  1.4.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) 
 
1.4.1.1. Tensile strength a nd elongation at break
 according to ISO 37. Tensile strength not 
less than 10 MPa and elongation at break not less than 250 per cent. 
 
1.4.1.2. Resistance to n-hexane  according to ISO 1817 with the following conditions: 
 
(a) medium: n-hexane 
(b) temperature: 23 °C (tolerance acc.to ISO 1817) 
(c) immersion period: 72 hours 
 Requirements:  
 (a) maximum change in volume 30 per cent (b) maximum change in tensile strength 35 per cent (c) maximum change in elongation at break 35 per cent 
 1.4.1.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10 °C). 
(b) exposure period: 24 and 336 hours. 
 After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 1.4.1.1.  Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours 
ageing compared to the elongation at break of the 24 hours aged material. 
 1.4.2. Tensile strength and elongation specific for thermoplastic material.  1.4.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. GSO STANDARD                                                                     GSO  /    
 
 
 108(b) tensile speed: 20 mm/min.  The material has to be conditioned for at least 21 days at 23 °C and 50 per cent relative humidity prior to testing.  
Requirements:  (a) tensile strength not less than 20 MPa. (b) elongation at break not less than 100 per cent.  
1.4.2.2. Resistance to n-hexane according to ISO 1817 with the following conditions: 
 (a) medium: n-hexane. (b) temperature: 23 °C (tolerance according to ISO 1817). (c) immersion period: 72 hours.  Requirements:  (a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 1.4.2.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10  °C). 
(b) exposure period: 24 and 336 hours. 
 After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 1.4.2.1.  Requirements:  (a) maximum change in tensile strength 20 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 50 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 
1.4.3. Resistance to ozone  1.4.3.1. The test has to be performed in compliance with Standard ISO 1431/1. GSO STANDARD                                                                     GSO  /    
 
 
 109 1.4.3.2. The test-pieces, which have to be stre tched to an elongation of 20 per cent shall 
have to be exposed to air of 40 °C with an ozone-concentration of 50 parts per 
hundred million during 120 hours. 
 1.4.3.3. No cracking of the test pieces is allowed.  
1.5. Specifications for uncoupled hose  1.5.1. Gas-tightness (permeability)  1.5.1.1. A hose at a free length of 1 m has to be connected to a container filled with liquid 
propane, having a temperature of 23 ° ± 2 °C. 
 1.5.1.2. The test has to be carried out in compliance with the method described in 
Standard ISO 4080. 
 1.5.1.3. The leakage through the wall of the hose shall not exceed 95 cm
3 per meter of 
hose per 24 h. 
 
1.5.2. Resistance at low temperature  1.5.2.1. The test has to be carried out in compliance with the method described in 
Standard ISO 4672-1978, method B. 
 
1.5.2.2. Test temperature: -40 °C ± 3 °C   or -20 °C ± 3 °C, if applicable.  1.5.2.3. No cracking or rupture is allowed.  1.5.3. Bending test  1.5.3.1. An empty hose, at a length of approximately 3.5 m must be able to withstand 
3,000 times the hereafter prescribed alte rnating-bending-test without breaking.  
After the test the hose must be capable  of withstanding the test-pressure as 
mentioned in paragraph 1.5.4.2. The test sh all be performed on both new hose and 
after ageing according to ISO 188 as prescribed in paragraph 1.4.2.3. and subsequently to ISO 1817 as prescribed in paragraph 1.4.2.2. 
 1.5.3.2.      GSO STANDARD                                                                     GSO  /    
 
 
 110    
Figure 1 (example only)
 
 
Distance between centres  (mm) 
(Figure 1) Hose inside diameter 
(mm) Bending radius 
([mm) 
 
(Figure 1) Vertical 
b Horizontal 
a 
up to 13 102 241 102 
13 to 16 153 356 153 
from 16 to 20 178 419 178 
  1.5.3.3. The testing-machine (Figure 1) shall cons ist of a steel frame, provided with two 
wooden wheels, with a rim-width of c.a. 130 mm.  The circumference of the wheels must be grooved for the guidance of the hose. The radius of the wheels, measured to the bottom of the groove, must be as 
indicated in paragraph 1.5.3.2. 
 The longitudinal median planes of both wheels must be in the same vertical plane and the distance between the wheel-centers must be in accordance with paragraph 1.5.3.2. Each wheel must be able to rotate freely round its pivot-centre.  A propulsion-mechanism pulls the hose ove r the wheels at a speed of four 
complete motions per minute. 
 1.5.3.4. The hose shall be S-shape-like installed over the wheels (see Figure 1).   The end, that runs over the upper wheel sh all be furnished with a sufficient mass 
as to achieve a complete snuggling of the hose against the wheels.  The part that 
runs over the lower wheel is attached to the propulsion-mechanism. 
  The mechanism must be so adjusted, that  the hose travels a total distance of 1.2 m 
in both directions. 
 1.5.4. Hydraulic-test-pressure and appointment of the minimum burst-pressure  1.5.4.1. The test has to be carried out in compliance with the method described in 
Standard ISO 1402. 
 1.5.4.2. The test-pressure of 1.5 times the worki ng pressure (MPa) shall be applied during GSO STANDARD                                                                     GSO  /    
 
 
 11110 minutes, without any leakage. 
 1.5.4.3. The burst pressure shall not be less than 45 MPa.  1.6. Couplings 
 1.6.1. The couplings shall be made from st eel or brass and the surface must be 
corrosion-resistant. 
 1.6.2. The couplings must be of the crimp-fitting type.  1.6.2.1. The swivel-nut must be provided with U.N.F.-thread.  1.6.2.2. The sealing cone of swivel-nut type must  be of the type with a half vertical 
angle of 45°. 
 1.6.2.3. The couplings can be made as swivel-nut type or as quick-connector type.  1.6.2.4. It shall be impossible to disconnect the quick-connector type without specific 
measures or the use of dedicated tools. 
 1.7. Assembly of hose and couplings  1.7.1. The construction of the couplings must be such, that it is not necessary to peel the 
cover unless the reinforcement of the hose consists of corrosion-resistant material. 
 
1.7.2. The hose assembly has to be subjected to an impulse test in compliance with 
Standard ISO 1436. 
 
1.7.2.1. The test has to be completed with ci rculating oil having a temperature of 93 °C, 
and a minimum pressure of 26 MPa. 
 
1.7.2.2. The hose has to be subjected to 150,000 impulses.  1.7.2.3. After the impulse-test the hose has to with stand the test-pressure as mentioned in 
paragraph 1.5.4.2. 
 1.7.3. Gas-tightness  1.7.3.1. The hose assembly (hose with couplings) has to withstand during five minutes a 
gas pressure of 1.5 times the working pressure (MPa) without any leakage. 
 1.8. Markings  1.8.1. Every hose must bear, at intervals of not  greater than 0.5 m, the following clearly GSO STANDARD                                                                     GSO  /    
 
 
 112legible and indelible identification marki ngs consisting of characters, figures or 
symbols. 
 1.8.1.1. The trade name or mark of the manufacturer.  
1.8.1.2. The year and month of fabrication.  1.8.1.3. The size and type-marking.  1.8.1.4. The identification-marking "CNG Class 0". 1.8.2. Every coupling shall bear the trade name or mark of the assembling manufacturer. 
 2. MEDIUM PRESSURE HOSES, CLASS 1 CLASSIFICATION  2.1. General specifications  2.1.1. The hose shall be so designed as to withstand a maximum working pressure of 
3 MPa. 
 2.1.2. The hose shall be so designed as to with stand temperatures as specified in Annex 
3O. 
 2.1.3. The inside diameter shall be in compliance with table 1 of Standard ISO 1307.  2.2. Hose construction  
2.2.1. The hose must embody a smooth-bore tube  and a cover of suitable synthetic 
material, reinforced with one or more interlayer(s). 
 
2.2.2. The reinforcing interlayer(s) has (have) to be protected by a cover against 
corrosion. 
  If for the reinforcing interlayer(s) co rrosion-resistant-material is used (i.e. 
stainless-steel) a cover is not required. 
 2.2.3. The lining and the cover must be smoot h and free from pores, holes and strange 
elements. 
  An intentionally provided puncture in th e cover shall not be considered as an 
imperfection. 
 2.3. Specifications and tests for the lining  2.3.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) GSO STANDARD                                                                     GSO  /    
 
 
 113 2.3.1.1. Tensile strength and elonga tion at break according to ISO 37. Tensile strength not 
less than 10 MPa and elongation at break not less than 250 per cent. 
 2.3.1.2. Resistance to n-pentane according to ISO 1817 with the following conditions: 
 
(a) medium: n-pentane 
(b) temperature: 23 °C (tolerance acc. to ISO 1817) 
(c) immersion period: 72 hours 
Requirements:   (a) maximum change in volume 20 per cent (b) maximum change in tensile strength 25 per cent (c) maximum change in elongation at break 30 per cent 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 2.3.1.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10 °C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test 
according to paragraph 2.3.1.1. 
 
Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 
2.3.2. Tensile strength and elongation specific for thermoplastic material. 
 
2.3.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. 
(b) tensile speed: 20 mm/min.  The material has to be conditioned for at least 21 days at 23 °C and 50 per cent relative humidity prior to testing. GSO STANDARD                                                                     GSO  /    
 
 
 114 Requirements:  (a) tensile strength not less than 20 MPa. (b) elongation at break not less than 100 per cent. 
 
2.3.2.2. Resistance to n-pentane according to ISO 1817 with the following conditions: 
 (a) medium: n-pentane. (b) temperature: 23 °C (tolerance according to ISO 1817). (c) immersion period: 72 hours.  Requirements:  (a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 
2.3.2.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10  °C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 2.3.2.1. 
 
Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 2.4. Specifications and test-method for the cover  2.4.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) 
 2.4.1.1. Tensile strength and elonga tion at break according to ISO 37. Tensile strength not 
less than 10 MPa and elongation at break not less than 250 per cent. GSO STANDARD                                                                     GSO  /    
 
 
 115 2.4.1.2. Resistance to n-hexane according to ISO 1817 with the following conditions:  
(a) medium: n-hexane 
(b) temperature: 23 °C (tolerance acc. to ISO 1817) 
(c) immersion period: 72 hours 
 Requirements:   (a) maximum change in volume 30 per cent (b) maximum change in tensile strength 35 per cent (c) maximum change in elongation at break 35 per cent 
 2.4.1.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10  °C) 
(b) exposure period: 24 and 336 hours  After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 2.4.1.1.  Requirements:  (a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 2.4.2. Tensile strength and elongation specific for thermoplastic material.  2.4.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. (b) tensile speed: 20 mm/min.  The material has to be conditioned for at least 21 days at 23 °C and 50 per cent relative humidity prior to testing.  Requirements:  (a) tensile strength not less than 20 MPa. (a) elongation at break not less than 100 per cent. GSO STANDARD                                                                     GSO  /    
 
 
 116 
2.4.2.2. Resistance to n-hexane according to ISO 1817 with the following conditions: 
 (a) medium: n-hexane. (b) temperature: 23 °C (tolerance according to ISO 1817). 
(c) immersion period: 72 hours.  Requirements:  (a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 2.4.2.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10 °C). 
(b) exposure period: 24 and 336 hours. 
 After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 2.4.2.1.  
Requirements: 
 (a) maximum change in tensile strength 20 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 50 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 2.4.3. Resistance to ozone  2.4.3.1. The test has to be performed in compliance with Standard ISO 1431/1.  2.4.3.2. The test-pieces, which have to be stre tched to an elongation of 20 per cent shall 
have to be exposed to air of 40 °C with an ozone-concentration of 50 parts per 
hundred million during 120 hours. 
 2.4.3.3. No cracking of the test pieces is allowed.  2.5. Specifications for uncoupled hose  GSO STANDARD                                                                     GSO  /    
 
 
 1172.5.1. Gas-tightness (permeability)  2.5.1.1. A hose at a free length of 1 m has to be connected to a container filled with liquid 
propane, having a temperature of 23 ° ± 2 °C. 
 2.5.1.2. The test has to be carried out in compliance with the method described in 
Standard ISO 4080. 
 
2.5.1.3. The leakage through the wall of the hose shall not exceed 95 cm
3 per meter of 
hose per 24 h. 
 
2.5.2. Resistance at low temperature  2.5.2.1. The test has to be carried out in compliance with the method described in 
Standard ISO 4672-1978, method B. 
 
2.5.2.2. Test temperature: -40 °C ± 3 °C   or -20 °C ± 3 °C, if applicable."  2.5.2.3. No cracking or rupture is allowed.  2.5.3. Bending test  2.5.3.1. An empty hose, at a length of approximately 3.5 m must be able to withstand 
3,000 times the hereafter prescribed alternating-bending-test without breaking.  After the test the hose must be capable  of withstanding the test-pressure as 
mentioned in paragraph 2.5.4.2.  The test  shall be performed on both new hose 
and after ageing according to ISO 188 as prescribed in paragraph 2.4.2.3. and subsequently to ISO 1817 as prescribed in paragraph 2.4.2.2. 
     2.5.3.2.           GSO STANDARD                                                                     GSO  /    
 
 
 118Figure 2 (example only)  
 
Distance between centres  [mm] 
(Figure 2) Hose inside diameter 
[mm] Bending radius 
[mm] 
 
(Figure 2) Vertical 
b Horizontal 
a 
up to 13 102 241 102 
13 to 16 153 356 153 
from 16 to 20 178 419 178 
  2.5.3.3. The testing-machine (Figure 2) shall c onsist of a steel frame, provided with 
two wooden wheels, with a rim-width of c.a. 130 mm. 
 
The circumference of the wheels must be grooved for the guidance of the hose. The radius of the wheels, measured to the bottom of the groove, must be as 
indicated in paragraph 2.5.3.2. 
 The longitudinal median planes of both wheels must be in the same vertical plane and the distance between the wheel-centres must be in accordance with paragraph 2.5.3.2.  Each wheel must be able to rotate freely round its pivot-centre.  A propulsion-mechanism pulls the hose ove r the wheels at a speed of four 
complete motions per minute. 
 2.5.3.4. The hose shall be S-shape-like installed over the wheels (see Figure 2).  
The end, that runs over the upper wheel sh all be furnished with a sufficient mass 
as to achieve a complete snuggling of the hose against the wheels.  The part that 
runs over the lower wheel is attached to the propulsion mechanism. The mechanism must be so adjusted, that the hose travels a total distance of 1.2 m 
in both directions. 
 2.5.4. Hydraulic-test-pressure   2.5.4.1. The test has to be carried out in compliance with the method described in 
Standard ISO 1402. 
 2.5.4.2. The test-pressure of 3 MPa shall be  applied during 10 minutes, without any 
leakage. 
 2.6. Couplings  GSO STANDARD                                                                     GSO  /    
 
 
 1192.6.1. If a coupling is mounted on the hose the following conditions have to be met:  2.6.2. The couplings shall be made from st eel or brass and the surface must be 
corrosion-resistant. 
 
2.6.3. The couplings must be of the crimp-fitting type.  2.6.4. The couplings can be made as swivel-nut type or as quick-connector type.  2.6.5. It shall be impossible to disconnect the quick-connector type without specific 
measures or the use of dedicated tools. 
 2.7. Assembly of hose and couplings  2.7.1. The construction of the couplings must be such, that it is not necessary to peel the 
cover unless the reinforcement of the hose consists of corrosion-resistant material. 
 2.7.2. The hose assembly has to be subjected to an impulse test in compliance with 
Standard ISO 1436. 
 
2.7.2.1. The test has to be completed with ci rculating oil having a temperature of 93 °C, 
and a minimum pressure of 1.5 times the maximum working pressure. 
 
2.7.2.2. The hose has to be subjected to 150,000 impulses.  2.7.2.3. After the impulse-test the hose has to with stand the test-pressure as mentioned in 
paragraph 2.5.4.2. 
2.7.3. Gas-tightness  2.7.3.1. The hose assembly (hose with couplings) has to withstand during five minutes a 
gas pressure of 3 MPa without any leakage. 
 2.8. Markings  2.8.1. Every hose must bear, at intervals of not  greater than 0.5 m, the following clearly 
legible and indelible identification marki ngs consisting of characters, figures or 
symbols. 
 2.8.1.1. The trade name or mark of the manufacturer.  2.8.1.2. The year and month of fabrication.  2.8.1.3. The size and type marking.  2.8.1.4. The identification-marking "CNG Class 1". GSO STANDARD                                                                     GSO  /    
 
 
 120 2.8.2. Every coupling shall bear the trade name or mark of the assembling manufacturer. 
 3. LOW PRESSURE HOSES, CLASS 2 CLASSIFICATION  
3.1. General specifications  3.1.1. The hose shall be so designed as to withstand a maximum working pressure of 
450 kPa. 
 3.1.2. The hose shall be so designed as to with stand temperatures as specified in Annex 
3O. 
 3.1.3. The inside diameter shall be in compliance with table 1 of Standard ISO 1307.  3.2. (Not allocated)  3.3. Specifications and tests for the lining  3.3.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) 
 3.3.1.1. Tensile strength and elongation at break according to ISO 37   Tensile strength not less than 10 MPa and elongation at break not less than 
250 per cent. 
 3.3.1.2. Resistance to n-pentane
 according to ISO 1817 with the following conditions: 
 
(a) medium: n-pentane 
(b) temperature: 23 °C (tolerance acc. to ISO 1817) 
(c) immersion period: 72 hours 
 Requirements:  
 (a) maximum change in volume 20 per cent (b) maximum change in tensile strength 25 per cent (c) maximum change in elongation at break 30 per cent 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 3.3.1.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temper ature = maximum operating temperature GSO STANDARD                                                                     GSO  /    
 
 
 121minus 10 ° C). 
(b) exposure period: 24 and 336 hours.  After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test 
according to paragraph 3.3.1.1.  Requirements:  (a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 3.3.2. Tensile strength and elongation specific for thermoplastic material.  3.3.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. (b) tensile speed: 20 mm/min.  The material has to be conditioned for at least 21 days at 23 °C and 50 per cent relative humidity prior to testing.  Requirements: 
 
(a) tensile strength not less than 20 MPa. (b) elongation at break not less than 100 per cent. 
 3.3.2.2. Resistance to n-pentane according to ISO 1817 with the following conditions:  
(a) medium: n-pentane. (b) temperature: 23 °C (tolerance according to ISO 1817). (c) immersion period: 72 hours.  Requirements:  (a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 GSO STANDARD                                                                     GSO  /    
 
 
 1223.3.2.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10 ° C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent 
relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 3.3.2.1.  Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 3.4. Specifications and test-method for the cover  3.4.1. Tensile strength and elongation for rubber material and for thermoplastic 
elastomers (TPE) 
 3.4.1.1. Tensile strength and elongation at break according to ISO 37   Tensile strength not less than 10 MPa and elongation at break not less than 
250 per cent. 
  3.4.1.2. Resistance to n-hexane
 according to ISO 1817 with the following conditions: 
 
(a) medium: n-hexane 
(b) temperature: 23 °C (tolerance acc. to ISO 1817) 
(c) immersion period: 72 hours 
 Requirements:  
 (a) maximum change in volume 30 per cent (b) maximum change in tensile strength 35 per cent (c) maximum change in elongation at break 35 per cent 
 3.4.1.3. Resistance to ageing according to ISO 188 with the following conditions:  
(a) temperature: 115 °C (test temper ature = maximum operating temperature 
minus 10 ° C). 
(b) exposure period: 24 and 336 hours. 
 GSO STANDARD                                                                     GSO  /    
 
 
 123After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test according to paragraph 3.4.1.1. 
 
Requirements: 
 
(a) maximum change in tensile strength 35 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 25 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 
3.4.2. Tensile strength and elongation specific for thermoplastic material.  3.4.2.1. Tensile strength and elongation at br eak according to ISO 527-2 with the 
following conditions: 
 
(a) specimen type: type 1 BA. (b) tensile speed: 20 mm/min. 
 
The material has to be conditioned for at least 21 days at 23 °C and 50 per cent relative humidity prior to testing.  Requirements:  (a) tensile strength not less than 20 MPa. (b) elongation at break not less than 100 per cent. 
 3.4.2.2. Resistance to n-hexane according to ISO 1817 with the following conditions:  
(a) medium: n-hexane. (b) temperature: 23 °C (tolerance according to ISO 1817). (c) immersion period: 72 hours. 
 
Requirements: 
 
(a) maximum change in volume 2 per cent. (b) maximum change in tensile strength 10 per cent. (c) maximum change in elongation at break 10 per cent. 
 
After storage in air with a temperature of 40 °C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 3.4.2.3. Resistance to ageing according to ISO 188 with the following conditions: 
 
(a) temperature: 115 °C (test temperat ure = maximum operating  temperature GSO STANDARD                                                                     GSO  /    
 
 
 124minus 10 °C). 
(b) exposure period: 24 and 336 hours. 
 
After ageing the specimens have to be conditioned at 23 °C and 50 per cent relative humidity for at least 21 days prior to carrying out the tensile test 
according to paragraph 3.4.2.1.  Requirements: 
 
(a) maximum change in tensile strength 20 per cent after 336 hours ageing 
compared to the tensile strength of the 24 hours aged material. 
(b) maximum change in elongation at break 50 per cent after 336 hours ageing 
compared to the elongation at break of the 24 hours aged material. 
 3.4.3. Resistance to ozone  3.4.3.1. The test has to be performed in compliance with Standard ISO 1431/1.  3.4.3.2. The test-pieces, which have to be stre tched to an elongation of 20 per cent shall 
have to be exposed to air of 40 °C and a relative humidity of 50 per cent ± 10 per 
cent with an ozone concentration of  50 parts per hundred million during 120 
hours. 
 3.4.3.3. No cracking of the test pieces is allowed.  3.5. Specifications for uncoupled hose  3.5.1. Gas-tightness (permeability)  3.5.1.1. A hose at a free length of 1 m has to be connected to a container filled with liquid 
propane, having a temperature of 23 ° ± 2 °C. 
 3.5.1.2. The test has to be carried out in compliance with the method described in 
Standard ISO 4080. 
 3.5.1.3. The leakage through the wall of the hose shall not exceed 95 cm
3 per meter of 
hose per 24 h. 
 
3.5.2. Resistance at low temperature  3.5.2.1. The test has to be carried out in compliance with the method described in 
Standard ISO 4672, method B. 
 GSO STANDARD                                                                     GSO  /    
 
 
 1253.5.2.2. Test temperature: -40 °C ± 3 °C    or -20 °C ± 3 °C, if applicable.  3.5.2.3. No cracking or rupture is allowed.  3.5.3. Resistance at high temperature  
3.5.3.1. A piece of hose, pressurized at 450 kPa, with a minimal length of 0.5 m must be 
put in an oven at a temperature of 120 °C ± 2 °C during 24 hours.  The test shall 
be performed on both new hose and af ter ageing according to ISO 188 as 
prescribed in paragraph 3.4.2.3. and subse quently to ISO 1817 as prescribed in 
paragraph 3.4.2.2. 
 
3.5.3.2. The leakage through the wall of the hose shall not exceed 95 cm
3 per meter of 
hose per 24 h. 
 
3.5.3.3. After the test the hose shall withsta nd the test pressure of 50 kPa during 10 
minutes.  The leakage through the wall of the hose shall not exceed 95 cm3 per 
meter of hose per 24 h. 
 3.5.4. Bending test  3.5.4.1. An empty hose, at a length of approximately 3.5 m must be able to withstand 
3,000 times the hereafter prescribed alternating-bending-test without breaking. 
 
3.5.4.2.                   (a = 102 mm;   b= 241 mm)           
Figure 3 (example only)
 
 
 
The testing machine (Figure 3) shall c onsist of a steel frame, provided with 
two wooden wheels, with a rim width of approx. 130 mm. The circumference of the wheels must be grooved for the guidance of the hose. The radius of the wheels, measured to the bottom of the groove, must be 102 mm. GSO STANDARD                                                                     GSO  /    
 
 
 126 The longitudinal median planes  of both wheels must be in the same vertical plane. 
 The distance between the wheel-centres must be vertical 241 mm and horizontal 
102 mm.  
Each wheel must be able to rotate freely round its pivot-centre.  A propulsion-mechanism pulls the hose ove r the wheels at a speed of four 
complete motions per minute. 
 3.5.4.3. The hose shall be S-shape-like installed over the wheels (see Figure 3).  
The end, that runs over the upper wheel, sh all be furnished with a sufficient mass 
as to achieve a complete snuggling of the hose against the wheels.  The part that 
runs over the lower wheel is attached to the propulsion mechanism. The mechanism must be so adjusted, that the hose travels a total distance of 1.2 m in both directions.  
3.6. Markings  3.6.1. Every hose must bear, at intervals of not  greater than 0.5 m, the following clearly 
legible and indelible identification marki ngs consisting of characters, figures or 
symbols. 
 3.6.1.1. The trade name or mark of the manufacturer.  
3.6.1.2. The year and month of fabrication. 
 3.6.1.3. The size and type marking.  3.6.1.4. The identification marking "CNG Class 2".  3.6.2. Every coupling shall bear the trade name or mark of the assembling manufacturer. 
  GSO STANDARD                                                                     GSO  /    
 
 
Annex 4C  
 
PROVISIONS REGARDING THE APPROVAL OF THE CNG FILTER 
  1. The purpose of this annex is to determin e the provisions regarding the approval of 
the CNG filter. 
 
2. Operating conditions  2.1. The CNG filter shall be so designed to ope rate at temperatures as specified in 
Annex 3O. 
 2.2. CNG filter shall be Classified with rega rd to the maximum working pressure (see 
paragraph 2 of this Regulation): 
 2.2.1. Class 0: The CNG filter shall be so desi gned to withstand a pressure of 1.5 times 
the working pressure (MPa). 
 2.2.2. Class 1 and Class 2: The CNG filter shall be so designed to withstand a pressure 
twice the working pressure. 
 2.2.3. Class 3: the CNG filter shall be so de signed to withstand a pressure twice the 
relief pressure of the pressure relief valve on which it is subject. 
 2.3. The materials used in the CNG filter which are in contact with CNG when 
operating, shall be compatible with this gas (see Annex 3D).  
 2.4. The component has to comply with th e test procedures for Class components 
according to the scheme in Figure 1-1 of paragraph 2 of this Regulation. 
 GSO STANDARD                                                                     GSO  /    
 
 
Annex 4D  
 
PROVISIONS REGARDING THE APPROVAL OF THE PRESSURE REGULATOR 
 1. The purpose of this annex is to determin e the provisions regarding the approval of 
the pressure regulator. 
 
2. Pressure regulator 
 2.1. The material constituting the regulator wh ich is in contact with the compressed 
natural gas when operating shall be compatib le with the test CNG.  In order to 
verify this compatibility, the procedure in Annex 3D shall be used. 
 2.2. The materials constituting the regulator which are in contact with the heat 
exchange medium of the regulator when operating, shall be compatible with that 
fluid. 
 2.3. The component shall comply with the test procedures provided for in Class 0 for 
the parts subject to high pressure and Cl ass 1, 2, 3 and 4 for the parts subject to 
medium and low pressure. 
 2.4. Durability test (continued operation) of pressure regulator:   The regulator shall be able to withst and 50,000 cycles without any failure when 
tested according to the following procedur e.  Where the stages of pressure 
regulation are separate, the service pressu re in sub-paragraphs (a) to (f) is 
considered to be the working pressure of the upstream stage. 
 (a) Recycle the regulator for 95 per cent of the total number of cycles at room 
temperature and at the service pressure .  Each cycle shall consist of flow 
until stable outlet pressure has been obtained, after which the gas flow shall be shut off by a downstream valve within 1 s, until the downstream lock-up pressure has stabilized.  Stabilized outlet pressures are defined as set pressure ±15 per cent for at least 5 s. 
 (b) Cycle the inlet pressure of the regul ator for 1 per cent of the total number of 
cycles at room temperature from 100 per cent to 50 per cent of the service 
pressure.  The duration of each cycle shall be no less than 10 s. 
 (c) Repeat the cycling procedure of (a) at 120 °C at the service pressure for 
1 per cent of the total number of cycles. 
 (d) Repeat the cycling procedure of (b) at 120 °C at the service pressure for 
1 per cent of the total number of cycles. 
 (e) Repeat the cycling procedure of (a) at -40 °C or -20 °C as applicable and 
50 per cent of service pressure for 1 pe r cent of the total number of cycles. 
 (f) Repeat the cycling procedure of (b) at -40 °C or -20 °C as applicable and 
50 per cent of service pressure for 1 pe r cent of the total number of cycles. 
 (g) At the completion of all tests indicated  in sub-paragraphs (a), (b), (c), (d), 
(e) and (f), the regulator shall be  leak proof (see Annex 3B) at the 
temperatures    of -40 °C or -20 °C, as applicable, and at the room temperature and at the temperature of +120 °C." GSO STANDARD                                                                     GSO  /    
 
 
 129 3. Classification and test pressures  3.1 The part of the pressure regulator which is in contact with the pressure of the 
container is regarded as Class 0. 
 
3.1.1. The Class 0 part of the pressure regulator  shall be leak-proof (see Annex 3B) at a 
pressure up to 1.5 times the working pressure  (MPa) with the outle t(s) of that part 
closed off. 
 3.1.2. The Class 0 part of the pressure regul ator shall withstand a pressure up to 1.5 
times the working pressure (MPa). 
 3.1.3. The Class 1 and Class 2 part of the pr essure regulator shall be leak-proof 
(see Annex 3B) at a pressure up to twice the working pressure. 
 3.1.4. The Class 1 and Class 2 part of the pre ssure regulator shall withstand a pressure 
up to twice the working pressure. 
 3.1.5. The Class 3 part of the pressure regulat or shall withstand a pressure up to twice 
the relief pressure of the pressure relief valve, on which it is subject. 
 3.2. The pressure regulator shall be so designed to operate at temperatures as specified 
in Annex 3O. 
  GSO STANDARD                                                                     GSO  /    
 
 
 Annex 4E  
 
PROVISIONS REGARDING THE APPROVAL OF THE PRESSURE AND 
TEMPERATURE SENSORS 
 
1. The purpose of this annex is to determin e the provisions regarding the approval of 
the pressure and temperature sensors. 
 
2. Pressure and temperature sensors  2.1. The material constituting the pressure and temperature sensors which is in contact 
with the CNG when operating shall be compa tible with the test CNG.  In order to 
verify this compatibility, the procedure in Annex 3D shall be used. 
 2.2. The pressure and temperature sensors are classified in a Class according to the 
scheme 1-1 in paragraph 2 of this Regulation. 
 3. Classification and test pressures  3.1 The part of the pressure and temperatur e sensors which is in contact with the 
pressure of the container is regarded as Class 0. 
 3.1.1. The Class 0 part of the pressure and temp erature sensors shall be leak-proof at a 
pressure up to 1.5 times the working pressure (MPa) (see Annex 3B). 
 3.1.2. The Class 0 part of the pressure a nd temperature sensors shall withstand a 
pressure up to 1.5 times the working pressure (MPa). 
 3.1.3. The Class 1 and Class 2 part  of the pressure and temperature sensors shall be leak-
proof at a pressure up to twice the working pressure (see Annex 3B). 
 3.1.4. The Class 1 and Class 2 part of the pressure and temperature sensors shall 
withstand a pressure up to twice the working pressure. 
 3.1.5. The Class 3 part of the pressure a nd temperature sensors shall withstand a 
pressure up to twice the relief pressure of  the pressure relief valve, on which it is 
subject. 
 3.2. The pressure and temperature sensors shall be so designed to operate at 
temperatures as specified in Annex 3O.  
 3.3. The electrical system, if existing, shall be  isolated from the body of the pressure 
and temperature sensors.  Isolation resistance shall be > 10 M Ω. 
  GSO STANDARD                                                                     GSO  /    
 
 
 Annex 4F  
 
PROVISIONS REGARDING THE APPROVAL OF THE FILLING UNIT 
(Receptacle) 
 
1. Scope  
 The purpose of this annex is to determin e the provisions regarding the approval of 
the filling unit. 
 
2. The filling unit  2.1. The filling unit shall comply  with the requirements laid down in paragraph 3. and 
shall have the dimensions of paragraph 4., if applicable. 
 2.2. Filling units designed in accordance with ISO 14469-1 first edition 2004-11-01 
1/ 
and meeting all the requirements therein ar e deemed to fulfil the requirements of 
paragraphs 3. and 4. of this annex. 
 
3. The filling unit test procedures  3.1. The filling unit shall be conform to the re quirements of Class 0 and follow the test 
procedures in Annex 3 with the following specific requirements. 
 
3.2. The material constituting the filling unit wh ich is in contact with the CNG when 
the device is in service shall be compatible with the CNG.  In order to verify this 
compatibility, the procedure of Annex 3D shall be used. 
 3.3. The filling unit shall be free from leakag e at a pressure of 1.5 times the working 
pressure (MPa) (see Annex 3B). 
 3.4. The filling unit shall withstand a pressure of 33 MPa.  3.5. The filling unit shall be so designed as to operate at temperatures as specified in 
Annex 3O. 
 3.6. The filling unit shall withstand a numbe r of 10,000 cycles in the durability test 
specified in Annex 3L. 
4. Filling unit dimensions  4.1. Figure 1 shows the dimensions of the filling unit for vehicles of categories M
1 
                     
1/ Road Vehicles Compressed Natural Gas (C NG) refuelling connector - part 1: 20 MPa 
(200 bar) connector. GSO STANDARD                                                                     GSO  /    
 
 
 132and N 1. 2/ 
 
                     
2/ As defined in Annex 7 to the Consolidated  Resolution on the Construction of Vehicles 
(R.E.3) (document TRANS/WP.29/78/Rev.1/Amend.2 as last amended by Amend.4). 
 GSO STANDARD                                                                     GSO  /    
 
 
 133Fig. 1: 20 MPa filling unit (receptacle) for M 1 and N 1 vehicles 
      
 
                           
 
  
1 Sealing surface equivalent to No. 110 O-ring of dimensions: Dimensions in millimetres 
 9.19 mm ± 0.127 mm ID Surface roughness  Ra 3.2 m 
 2.62 mm ± 0.076 mm width 
Sealing surface finish: 0.8 m to 0.05 m 
Material hardness: 75 Rockwell (HRB 75) minimum 
 a Minimum length of the receptacle which is clear of provisions for attachement of receptacle or protective caps.This area shall be kept free of all components. Key GSO STANDARD                                                                     GSO  /    
 
 
 Annex 4G  
 
PROVISIONS REGARDING THE APPROVAL OF GAS FLOW ADJUSTER AND 
GAS/AIR MIXER OR GAS INJECTOR 
 
1. The purpose of this annex is to determin e the provisions regarding the approval of 
the gas flow adjuster and gas/air mixer or gas injector. 
 
2. Gas/air mixer or gas injector  2.1. The material constituting the gas/air mixer or  gas injector which is in contact with 
CNG shall be compatible with the CNG.  In order to verify this compatibility, the 
procedure specified in Annex 3D shall be used. 
 2.2. The gas/air mixer or gas injector shall conform to the requirements of Class 1 or 
2 components, according to their Classification. 
 2.3. Test pressures  2.3.1. The gas/air mixer or gas injector of Cl ass 2 shall withstand a pressure twice the 
working pressure. 
 2.3.1.1. The gas/air mixer or gas injector of Class 2 shall be free from leakage at a 
pressure twice the working pressure. 
 2.3.2. The gas/air mixer or gas injector of Class 1 and Class 2 shall be so designed to 
operate at temperatures as specified in Annex 3O. 
 2.4. Electrical operated components containing CNG shall comply with the following: 
 
(a) They shall have a separate ground connection; (b) The electrical system of the component shall be isolated from the body; (c) The gas injector shall be in clos ed position when the electric current is 
switched off. 
 3. Gas flow adjuster  3.1. The material constituting the gas flow adju ster which is in contact with the CNG 
shall be compatible with the CNG.  In  order to verify this compatibility the 
procedure specified in Annex 3D has to be used. 
 3.2. The gas flow adjuster shall conform to requirements of Class 1 or 2 components, 
according to their Classification. 
 3.3. Test pressures GSO STANDARD                                                                     GSO  /    
 
 
 135 3.3.1. The gas flow adjuster of Class 2 sha ll withstand a pressure twice the working 
pressure. 
 3.3.1.1. The gas flow adjuster of Class 2 shall be  free from leakage at a pressure twice the 
working pressure. 
 
3.3.2. The gas flow adjuster of Class 1 and Cl ass 2 shall be so designed to operate at 
temperatures as specified in Annex 3O. 
 3.4. Electrical operated components containing CNG shall comply with the following: 
 
(a) They shall have a separate ground connection; (b) The electrical system of the component shall be isolated from the body. 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 4H  
 
PROVISIONS REGARDING THE APPROVAL OF THE ELECTRONIC CONTROL UNIT 
 
 1. The purpose of this annex is to determin e the provisions regarding the approval of 
the electronic control unit. 
 
2. Electronic control unit  2.1. The electronic control unit can be any device which controls the CNG demand of 
the engine and establishes the cut-off of the automatic valve in case of a broken 
fuel supply pipe or in case of stalling of the engine, or during a crash.  
 2.2. The switching off delay of the automatic va lve after stalling of the engine may not 
be more than 5 seconds. 
 2.3. The device may be equipped with an automatic ignition advance timing adjuster 
integrated in the electronic module or separated. 
 2.4. The device may be integrated with dummy injectors to permit a correct 
functioning of the gasoline electronic control unit during CNG operation. 
 2.5. The electronic control unit shall be so designed to operate at temperatures as 
specified in Annex 3O. 
   GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3  
 
TEST PROCEDURES 
 
1. Classification  1.1. CNG components for use in vehicles sha ll be classified with regard to the 
maximum working pressure and functi on, according to paragraph 2 of this 
Regulation.  
 
1.2 The classification of the components de termines the tests which have to be 
performed for type-approval of the components or parts of the components. 
 2. Applicable test procedures:   In table 5.1 below the applicable test procedures dependent on the classification 
are shown. 
 
Table 5.1
 
 
Test Class 0 Class 1 Class 2 Class 3 Class 4 Paragraph 
Overpressure or strength X X X X O 5A 
External leakage X X X X O 5B 
Internal leakage A A A A O 5C 
Durability tests A A A A O 5L 
CNG compatibility A A A A A 5D 
Corrosion resistance X X X X X 5E 
Resistance to dry heat A A A A A 5F 
Ozone ageing A A A A A 5G 
Burst/destructive tests X O O O O 5M 
Temperature cycle A A A A O 5H 
Pressure cycle X O O O O 5I 
Vibration resistance A A A A O 5N 
Operating temperatures X X X X X 5O 
 
X = Applicable 
O = Not applicable A = As applicable  Remarks: (a) Internal leakage:  Applicable if the Class of the component consists of 
internal valve seats that are normally closed during engine "OFF" condition. 
(b) Durability test:  Applicable if th e Class of the component consists of 
integral parts that will move repeatedly during engine operation. 
(c) CNG compatibility, resistance to dry h eat, ozone ageing:  Applicable if the GSO STANDARD                                                                     GSO  /    
 
 
 138class of the component consists of synthetic / non-metallic parts. 
(d) Temperature cyclic test:  Applicable if the class of the component consists 
of synthetic / non-metallic parts. 
(e) Vibration resistance test:  Applicable if the Class of the component consists 
of integral parts that will move repeatedly during engine operation. 
 
The materials used for the components shall have written specifications that 
fulfil at least or exceed the (test) requirements laid down in this annex with respect to: 
 
(a) temperature (b) pressure (c) CNG compatibility (d) durability 
 3. General requirements  3.1. Leakage tests shall have to be conducted with pressurized gas like air or nitrogen. 
 3.2. Water or another fluid may be used to obtain the required pressure for the 
hydrostatic strength test. 
 3.3. The test period for leakage- and hydrosta tic strength-tests shall be not less than 
3 minutes. 
  GSO STANDARD                                                                     GSO  /    
 
 Annex 3A  
 
OVERPRESSURE TEST (STRENGTH TEST) 
 
1. A CNG containing component shall withst and without any visible evidence of 
rupture or permanent distortion a hydraulic  pressure of 1.5-2 times the maximum 
working pressure during minimal 3 minutes at room temperature with the outlet of 
the high-pressure part plugged.  Water or  any other suitable hydraulic fluid may 
be used as a test medium. 
 
2. The samples, previously subjected to th e durability test of Annex 3L are to be 
connected to a source of hydrostatic pr essure.  A positive shut-off valve and a 
pressure gauge, having a pressure of not less than 1.5 times nor more than 2 times the test pressure, are to be installed in the hydrostatic pressure supply piping. 
 3. Table 5.2 below shows the working and burst test pressures according to the 
Classification of paragraph 2 of this Regulation. 
 
Table 5.2
 
 
Classification 
of component Working 
pressure 
[kPa] Overpressure 
 
[kPa] 
 
Class 0 3000<p<26000 1.5 times the working 
pressure 
Class 1 450<p<3000 1.5 times the working 
pressure 
Class 2 20<p<450 2 times the working pressure 
Class 3 450<p<3000 2 times the relief pressure 
 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3B  
 
EXTERNAL LEAKAGE TEST 
 
1. A component shall be free from leak age through stem or body seals or other 
joints, and shall not show ev idence of porosity in casting when tested as described 
in paragraphs 2. and 3. of this annex at any aerostatic pressure between 0 and the 
pressure shown in table 5.2. 
 
2. The test shall be performed at the following conditions:  
(a) at room temperature (b) at the minimum operating temperature (c) at the maximum operating temperature 
 
The maximum and minimum operating temperatures are given in Annex 3O. 
 3. During this test the equipment under test (EUT) will be connected to a source of 
aerostatic pressure.  An automatic valve and a pressure gauge having a pressure 
range of not less than 1.5 times nor more th an 2 times the test pressure are to be 
installed in the pressure supply piping.  The pressure gauge is to be installed 
between the automatic valve and the samp le under test.  While under the applied 
test pressure, the sample should be submerged in water to detect leakage or any other equivalent test method (flow measurement or pressure drop). 
 4. The external leakage must be lower than the requirements stated in the annexes or 
if no requirements are mentioned the exte rnal leakage shall be lower than 15 
cm
3/hour. 
 
5. High temperature test   A CNG containing component sh all not leak more than 15 cm
3/hour with the 
outlet plugged when submitted to a ga s pressure, at maximum operating 
temperature as indicated in Annex 3O, e qual to the maximum working pressure.  
The component shall be conditioned for at least 8 hours at this temperature. 
 6. Low temperature test  
 A CNG containing component sh all not leak more than 15 cm
3/hour with the 
outlet plugged when submitted to a gas pressure, at the minimum operating 
temperature, equal to the maximum working pressure as declared by the manufacturer.  The component shall be c onditioned for at least 8 hours at this 
temperature.GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3C  
 
INTERNAL LEAKAGE TEST 
 
1. The following tests are to be conducted on samples of valves or filling unit which 
have previously been subjected to the external leak test of Annex 3B above. 
 
2. The seat of the valves, when in the clos ed position, shall be free from leakage at 
any aerostatic pressure between 0 to 1.5 times the working pressure (kPa). 
 
3. A non-return valve provided with a resilient seat (elastic), when in the closed 
position, shall not leak when subjected to  any aerostatic pressure between 0 and 
1.5 times the working pressure (kPa). 
 4. A non-return valve provided with a meta l-to-metal seat, when in the closed 
position, shall not leak at a rate exceeding 0.47 dm
3/s when subjected to an 
aerostatic pressure difference of 138 kPa effective pressure. 
 
5. The seat of the upper non-return valve used  in the assembly of  a filling unit, when 
in the closed position, shall be free from  leakage at any aerostatic pressure 
between 0 and 1.5 times the working pressure (kPa). 
 
6. The internal leakage tests are conducte d with the inlet of the sample valve 
connected to a source of aerostatic pressu re, the valve in the closed position, and 
with the outlet open.  An automatic valve and a pressure gauge having a pressure 
range of not less than 1.5 times nor more th an 2 times the test pressure are to be 
installed in the pressure supply piping.  The pressure gauge is to be installed 
between the automatic valve and the samp le under test.  While under the applied 
test pressure, observations for leakage are to be made with the open outlet 
submerged in water unless otherwise indicated. 
 7. Conformance with paragraphs 2. to 5. is  to be determined by connecting a length 
of tubing to the valve outlet.  The open e nd of this outlet tube is to be located 
within an inverted graduated cylinder wh ich is calibrated in cubic centimeters.  
The inverted cylinder is to be closed by a water tight seal.  The apparatus is to be 
adjusted so that: 
 
(a) the end of the outlet tube is located approximately 13 mm above the water 
level within the inverted graduated cylinder, and  
(b) the water within and exterior to the gr aduated cylinder is at the same level.  
With these adjustments made, the water level within the graduated cylinder is to be recorded.  With the valve in the closed position assumed as the result of normal operation, air or nitrogen at  the specified test pressure is to 
be applied to the valve inlet for a te st period of not less than 2 minutes.  
During this time, the vertical position of the graduated cylinder is to be GSO STANDARD                                                                     GSO  /    
 
 
 142adjusted, if necessary, to maintain the same water level within and exterior 
to it. 
 
At the end of the test period and with the water within and exterior to the 
graduated cylinder at the same level, th e level of water within the graduated 
cylinder is again recorded.  From the change of volume within the graduated 
cylinder, the leakage rate is to be  calculated according to the following 
formula:  
 
⎟
⎠⎞⎜
⎝⎛
101.6P . T273 . t60 . V = V t 1  
 
where: 
 
V1 =  leakage rate, cubic centimetres of air or nitrogen per hour. 
 V
t =  increase in volume within graduated cylinder during test. 
 t =  time of test, minutes.  P =  barometric pressure during test, in kPa.  T =  ambient temperature during test, in K. 
 
8. Instead of the method described above, leakage may be measured by a flowmeter 
installed on the inlet side of the valve under test.  The flowmeter shall be capable of indicating accurately, for the test fl uid employed, the maximum leakage flow 
rates permitted. 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3D  
 
CNG COMPATIBILITY TEST 
 
1. A synthetic part in contact with CNG sh all not show excessive volume change or 
loss of weight. 
 Resistance to n-pentane according to ISO 1817 with the following conditions: 
 
(a) medium: n-pentane 
(b) temperature: 23 °C (tolerance acc.to ISO 1817) 
(c) immersion period: 72 hours 
 
2. Requirements:    maximum change in volume 20 per cent  
 After storage in air with a temperature of 40  
°C for a period of 48 hours the mass 
compared to the original value may not decrease more than 5 per cent. 
 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3E  
 
CORROSION RESISTANCE TEST 
 
 Test procedures : 
 1. A metal CNG containing component sh all comply with the leakage tests 
mentioned in Annexes 5B and 5C and after having been submitted to 144 hours 
salt spray test according to ISO 15500-2, with all connections closed. 
 2. A copper or brass CNG cont aining component shall comply with the leakage tests 
mentioned in Annexes 5B and 5C and after having been submitted to 24 hours 
immersion in ammonia according to ISO CD 15500-2 with all connections closed. 
 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3F  
 
RESISTANCE TO DRY HEAT 
 
1. The test has to be done in compliance with ISO 188.  The test piece has to be 
exposed to air at a temperature equal to the maximum operating temperature for 168 hours. 
 
2. The allowable change in tensile strength should not exceed + 25 per cent.  The 
allowable change in ultimate elongation shall not exceed the following values: 
 
Maximum increase 10 per cent Maximum decrease 30 per cent 
  GSO STANDARD                                                                     GSO  /    
 
 
 ANNEX 3G  
 
OZONE AGEING 
 
1. The test has to be in compliance with ISO 1431/1.    The test piece, which has to be stresse d to 20 per cent elongati on shall be exposed 
to air at 40 °C with an ozone concentration of 50 parts per hundred million during 
72 hours. 
 2. No cracking of the test piece is allowed.    GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3H  
 
TEMPERATURE CYCLE TEST 
 
A non metallic part containing CNG shall comp ly with the leakage tests mentioned in 
Annexes 5B and 5C after having been subm itted to 96 hours temperature cycle from the 
minimum operating temperature up to the ma ximum operating temperature with a cycle 
time of 120 minutes, under maximum working pressure. 
 
__________ 
 
 
Annex 3I  
 
PRESSURE CYCLE TEST APPLICABLE ONLY TO CYLINDERS (SEE ANNEX 2) 
 
_________ 
 
 
Annexes 5J and 5K  - Not allocated 
 
__________ 
  
Annex 3L
 
 
DURABILITY TEST (CONTINUED OPERATION) 
 
Test method  
 The component shall be connected to a source of  pressurised dry air or nitrogen by means of a 
suitable fitting and subjected to the number of cy cles specified for that specific component. A 
cycle shall consist of one opening and one closi ng of the component within a period of not less 
than 10 ± 2 seconds.  
(a) Room temperature cycling
 
 
 The component shall be operated through 96 per cent of the total cycles at room 
temperature and at rated service pressu re. During the off cycle the down stream 
pressure of the test fixture should be a llowed to decay to 50 per cent of the test 
pressure.  After that, the components shall comply with the leak age test of Annex 
3B at room temperature. It is allowed to in terrupt this part of the test at 20 per cent 
intervals for leakage testing. 
 
(b) High temperature cycling  GSO STANDARD                                                                     GSO  /    
 
 
 148  The component shall be operated through 2 per cent of the total cycles at the 
appropriate maximum temperature specifi ed at rated service pressure.  The 
component shall comply with the leakage test of Annex 3B at the appropriate 
maximum temperature at the completion of the high temperature cycles. 
 
(c) Low temperature cycling
 
 
 The component shall be operated through 2 per cent of the total cycles at the 
appropriate minimum temperature specifi ed at rated service pressure. The 
component shall comply with the leakage test of Annex 3B at the appropriate 
minimum temperature specified at the co mpletion of the low temperature cycles. 
 
 Following cycling and leakage re-test, the component shall be capable of 
completely opening and closing when a tor que not greater than that specified in 
Table 5.3 is applied to the component handl e in a direction to open it completely 
and then in the reverse direction. 
 
Table 5.3  
 
Component inlet size (mm) Max. torque (Nm) 
6 1.7 
8 or 10 2.3 
12 2.8 
 
This test shall be conducted at the appropriate maximum temperature specified, 
and shall be repeated at a temperature of -40 °C. 
 GSO STANDARD                                                                     GSO  /    
 
 
 Annex 3M  
 
BURST/DESTRUCTIVE TEST APPLICABLE ONLY TO CYLINDERS (SEE ANNEX 2) 
 
_________ 
 
 
Annex 3N  
 
VIBRATION RESISTANCE TEST 
 All components with moving parts shall remain  undamaged, continue to operate, and comply 
with the component's leakage tests after 6 hours of  vibration in accordance with the following test 
method. 
 
Test method
 
 
The component shall be secured in an apparatus and vibrated for 2 hours at 17 Hz with an amplitude of 1.5 mm (0,06 in.) in each of three orientation axes.  On completion of 6 hours of 
vibration the component shall comply with Annex 3C.  GSO STANDARD                                                                     GSO  /    
 
 
 ANNEX 3O  
 
OPERATING TEMPERATURES 
 
  
 Engine compartment Assembled on the 
engine On board 
Moderate - 20 °C ÷ 105 °C - 20 °C ÷ 120 °C - 20 °C ÷ 85 °C 
Cold - 40 °C ÷ 105 °C - 40 °C ÷ 120 °C - 40 °C ÷ 85 °C 
 GSO STANDARD                                                                     GSO  /    
 
 
 
Annex 4  
 
PROVISIONS REGARDING CNG IDENTIFICATION MARK FOR PUBLIC SERVICE 
VEHICLES 
 
  
 
             The sign consists of a sticker which must be weather resistant.  The colour and dimensions of the sticker must fulfil the following requirements: 
 Colours: 
Background: green Border: white or white reflecting Letters: white or white reflecting 
 Dimensions 
Border width: 4 - 6 mm 
Character height: 
≥ 25 mm 
Character thickness: ≥ 4 mm 
Sticker width: 110 - 150 mm 
Sticker height:  80 - 110 mm   
 
The word "CNG" must be centred in the middle of the sticker.   
 
 
    GSO STANDARD                                                                     GSO  /    
 
 
 152Annex 5  
 GSO STANDARD                                                                     GSO  /    
 
 
 153
 GSO STANDARD                                                                     GSO  /    
 
 
 154  GSO STANDARD                                                                     GSO  /    
 
 
 155
 GSO STANDARD                                                                     GSO  /    
 
 
 156  GSO STANDARD                                                                     GSO  /    
 
 
 157
 GSO STANDARD                                                                     GSO  /    
 
 
 158   GSO STANDARD                                                                     GSO  /    
 
 
 159
 GSO STANDARD                                                                     GSO  /    
 
 
 160