Reference number  
DRS 128: 2019  
© RSB 2019  
 
 
 RWANDA 
STANDARD  DRS 
128 
 
2nd edition  
2019 -xx-xx 
 
Rotational moulded polyethylene water        
storage tanks — Specification  
 
  DRS 128: 2019  
©RSB 2019 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2019  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw  DRS 128: 2019  
iii                ©RSB 2019  - All rights reserved  
 
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and defi nitions  ................................ ................................ ................................ ..................  1 
4 Requirements  ................................ ................................ ................................ ................................  4 
4.1 Materials  ................................ ................................ ................................ ................................ ........  4 
4.2 Carbon black content  ................................ ................................ ................................ ...................  4 
4.3 Catalyst  ................................ ................................ ................................ ................................ ..........  4 
4.4 Fillers and pigments  ................................ ................................ ................................ .....................  5 
4.5 Types  ................................ ................................ ................................ ................................ .............  5 
4.6 Fittings  ................................ ................................ ................................ ................................ ...........  6 
4.7 Sizes ................................ ................................ ................................ ................................ ...............  6 
4.8 Net capacity  ................................ ................................ ................................ ................................ .. 6 
4.9 Design parameters  ................................ ................................ ................................ .......................  6 
4.10  Dimensions and tolerances  ................................ ................................ ................................ .........  7 
5 Quality of finish  ................................ ................................ ................................ ............................  8 
6 Testing  ................................ ................................ ................................ ................................ ...........  8 
6.1 Resistance to deformatio n ................................ ................................ ................................ ..........  8 
6.2 Tensile strength  ................................ ................................ ................................ ............................  8 
6.3 Flexural strength  ................................ ................................ ................................ ..........................  8 
6.4 Hydrostatic pressure head  ................................ ................................ ................................ ..........  8 
6.5 Routine test  ................................ ................................ ................................ ................................ ... 8 
7 Sampling  ................................ ................................ ................................ ................................ ....... 9 
8 Marking  ................................ ................................ ................................ ................................ ..........  9 
9 Transportation  ................................ ................................ ................................ ..............................  9 
10 Workmanship  ................................ ................................ ................................ ..............................  10 
Annex  A (normative)  Determination of carbon black content  ................................ ...........................  11 
A.1 Apparatus  ................................ ................................ ................................ ................................ .... 11 
A.2 Reagents  ................................ ................................ ................................ ................................ ..... 11 
A.3 Procedure  ................................ ................................ ................................ ................................ .... 11 
A.4 Calculation  ................................ ................................ ................................ ................................ .. 11 
Annex  B (normative)  Determination of carbon black dispersion in polyethylene materials  ..........  13 
B.1 Procedure  ................................ ................................ ................................ ................................ .... 13 
B.2 Reporting  ................................ ................................ ................................ ................................ ..... 13 
Annex  C (normative)  Determination of effect of heavy metals on water quality  .............................  14 
C.1 Method of extraction  ................................ ................................ ................................ ..................  14 
C.2 Method of analysis  ................................ ................................ ................................ .....................  14 
Annex  D (normative)  Determination of Resistance to Deformation test  ................................ ..........  15 
D.1 Method 1 for cylindrical vertical tank  ................................ ................................ .......................  15 
D.2 Method 2 for rectangular loft tank  ................................ ................................ ............................  15 
Annex  E (normative)  Determination of tensile properties  ................................ ................................ .. 17 
E.1 Apparatus  ................................ ................................ ................................ ................................ .... 17 
E.2 Test specimens  ................................ ................................ ................................ ...........................  17 
E.3 Number of test specimens  ................................ ................................ ................................ ........  17 
E.4 Speed of testing  ................................ ................................ ................................ ..........................  18 
E.5 Procedure  ................................ ................................ ................................ ................................ .... 18 
E.6 Calculation and expr ession of results  ................................ ................................ .................  1819 
E.7 Test report  ................................ ................................ ................................ ................................ ... 19 
Annex  F (normative)  Determination of Hydrostatic pressure head  ................................ ..................  24 
Annex  G (informative)  Recommendations for installation and fittings of tanks  .............................  25 DRS 128: 2019  
©RSB 2019 - All rights reserved                  iv 
 G.1 Tank installation ................................ ................................ ................................ .........................  25 
G.2 Fittings  ................................ ................................ ................................ ................................ ........  25 
 DRS 128: 2019  
v                ©RSB 2019  - All rights reserved  
 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 128: 2019  was prepared by Technical Committee RSB/TC 048, Plastic tanks, pipes, accessories and 
related products . 
In the preparation of this standard, reference was made to the following standard  (s): 
IS 12701:1996 Rotational moulded polyethylene water storage tanks  
ASTM D1998 Standard specification for polyethylene upright storage tanks  
SLS 1174:1998 Poly ethylene water storage tanks — Specification  
KS 1567:2005 Rotational moulded polyethylene water storage tanks -Specification  
ARMSA South African Tank Standard  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second  edition  cancels and replaces the first  edition (RS 128:2012 ) which has  been technically revised.  
The following organizations were represented on the Technical Committee on  Plastic tanks, pipes, accessories 
and related products  RSB/TC 048 in the preparation of this standard.  
ROTO Ltd  
Rwanda plastic industries  
Ecopla stics 
SOIMEX Plastic  
Global community  
Rwanda  Standards Board  (RSB) – Secretariat 
1                ©RSB 2019  - All rights reserved  
 
 Rotational moulded polyethylene water storage tanks — Specification  
1 Scope  
This Draft Rwanda Standard prescribes the requirements , sampling and test methods for rotational moulded 
polyethylene water storage tanks (closed and open top tank) .  
The standard do es not cover mobile water tanks,  horizontal cylindrical water tanks and  underground tanks.   
This standard is applicable to both open -topped and closed -topped water storage tanks subjected to the 
following two conditions:  
a) own hydrostatic head of water;  
b) uniform flat base support.  
The nominal service temperature is 1 °C to 50 °C.  
2 Normative references  
The following documents are referred to in the text in such a way that some or all of their content constitutes 
requirements of this document.  For dated references, only the edition cited applies. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
ISO 1209 -2; Rigid cellular plastics — Determination of flexural properties — Part 2: Determination on flexural 
strength and apparent flexural  modulas of elasticity  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply.  
3.1 
net capacity (actual)  
net total volume of water contained between the lowest level of the overflow and lowest level of outlet (se e 
Figures 1 and 2)  
3.2 
gross capacity (nominal)  
the total enclosed volume of the tank including any space, which may not be capable of being filled with water  
3.3 
mould parting  
circumferential line visible only on the external surface of the tank correspon ding to a parting joint of the mould 
required for rotational moulding (see Figures 1 and 2)  
3.4 
overall height   
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 height of the finished empty tank at its highest point, including the top rim of the manhole and lid of the tank 
(see Figures 1 and 2)  
3.5 
effective height  
height of the finished empty tank from its base to the point where overflow connection is provided for the purpose 
of limiting water storage capacity (see Figures 1 and 2)  
3.6 
overall diameter  
maximum outer diameter of finished empty tank measured at its base (see Figures 1 and 2)  
3.7  
man-hole/hand -hole 
a hole of suitable internal diameter provided at the top of the tank for the purpose of inspection of internal surface 
and entry into the tank (see Figure 1).  
 
Figure 1— typical  perspective view of closed top tank  
RCC — Reinforced  cement concrete  
PCC —   Pre-cast cement concrete  
 
3                ©RSB 2019  - All rights reserved  
 
  
Figure 2— typical  view of open top tank  
3.8  
internal diameter of man -hole/hand -hole 
internal diameter of the rim of the manhole measured as the mean of two perpendicular diameters (see Figures 
1 and 2)  
3.9 
rotational molding  
three -stage commercial process consisting of loading the mold with powdered resin,  fusing the resin by heating 
while rotating the mold abou t more than one axis, and cooling and removing the molded article  
3.10 
service factor , n  
number less than 1.0 (which takes into consideration all the variables and degrees of safety involved in a 
polyethylene storage tank installation) which is multiplied  by the hydrostatic design basis to give the design 
hoop stress.  
3.11  
tensile stress  
tensile load per unit area of minimum original cross section within the narrow parallel portion, carried by the test 
specimen at any moment. It is expressed in N/mm2 (force per square millimetre).  
 
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 3.12 
elongation  
increase in distance between references likes on the narrow parallel portion of the test specimen, due to a 
tensile load, and expressed as a percentage of the initial distance between the reference lines.  
3.13 
yield point  
first point on the load/extension curve at which an increase in extension occurs without an increase in load.  
NOTE  In cases where the yield point is not well defined by the load extension curve, it is frequently necessary to define 
an offset y ield point. This is done by specifying a point on the load extension curve where the curve departs from linearity 
by a specified percentage elongation or extension (see Figure 10).  
3.14 
elastic modulus  
ratio of stress to corresponding strain within the ran ge of the greatest stress that the material is capable of 
sustaining without any deviation of proportionality of stress to strain.  
4 Requirements  
4.1 Materials  
4.1.1 The material for construction of the tank and lid, which comes into contact with water, shall not impart 
any taste, colour or odour to water; they shall neither have any toxic effect nor contaminate water thereby 
making it unpotable.  
4.1.2 Water tanks meant f or outdoor use shall be manufactured from virgin polyethylene materials intended 
for the rotational molding process (resin). The addition of not more than 10 percent of the manufacturers own 
reworked material resulting from the manufacture of tanks only ac cording to this standard is permissible. No 
other reworked or recycled waste material from any other source or filler shall be used in the manufacture of 
tanks 
4.1.3 All polyethylene resin material shall contain a minimum of a U.V. 8 stabilizer as compound ed by the 
resin manufacturer.   
4.1.4 Each resin used in designing tanks covered by this specification shall have hydrostatic -hoop -stress data 
available.  
4.2 Carbon black content  
4.2.1 Carbon black pigment if added, to the moulding material for the outer laye r or the exposed layer, shall 
be not less than 2.5 ± 0.5 % when tested in accordance with Annex A.  
4.2.2 The carbon black or any other pigment added shall be uniformly dispersed in the material, when tested 
in accordance with Annex B.  
4.3 Catalyst  
The total amount of inorganic present in polyethylene shall not exceed 0.2 % (m/m) when tested by atomic 
absorption method and in accordance with Annex C. An alternative method of testing for the metals shall be by 
x-ray fluorescence, where the atomic absorption met hod may not be applicable or just non -operational.   
5                ©RSB 2019  - All rights reserved  
 
 4.4 Fillers and pigments  
The plastic shall not contain any filler. Pigments may be added as desired by the customer, or as designated 
by polymer processing companies, but shall not exceed 0.5% dry blended, and  2% compounded in, of the total 
weight.  
NOTE The excessive  use of dry -blended pigments may result in an effect on physical properties, that is, impact 
strength.  
4.5 Types  
There shall be two types of tanks vis -à-vis:  
a) cylindrical vertical tanks (closed and open -end); and  
b) rectangular loft tanks (see Figure 3 a), and b)  
 
Figure 3a) — cylindrical  vertical with closed top  
 
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Figure 3 b) — Rectangular loft tank  
4.6 Fittings  
It shall be the prerogative of the manufacturer to provide as much information as is possible to the consumer 
regarding fittings.  
NOTE  Refer on Annex G for tank and fitting installations  
4.7 Sizes  
Tank sizes will vary in accordance with the customer’s requirements.  
4.8 Net capacity  
When filled to the lowest level of overflow, a nd the volume attained measured, tanks shall discharge the capacity 
marked on it.  
4.9 Design parameters  
4.9.1 The design wall thickness shall be determined by appropriate engineering design methods, which may 
include finite element analysis, for the nominated  service temperature .  
4.9.2 The minimum required wall thickness (T) of a cylindrical straight walled shell (unsupported portion of 
a tank) at any fluid level shall be determined from the following equation:  
T = P X OD / (2δ)  
P = 0.0098 × SG × H (MPa)  
δ= HDB × n 
 
7                ©RSB 2019  - All rights reserved  
 
 Where:  
T = wall thickness, mm,  
P = pressure, MPa  
SG = specific gravity of fluid, g/cm3  
H = fluid head, m  
OD = outside diameter of tank, mm, and  
δ = hydrostatic design stress, MPa.  
 n = Service factor  
4.9.3 Hydrostatic pressure value is determined by the height (H) of the liquid container and the density (SG) 
of the liquid. The tank walls have to be made to resist this pressure at different levels of water storage. Basically, 
the taller the tank, the greater the pressure on lower tank walls  
4.9.4 The hydrostatic design stress that is used to determine the minimum wall thickness at any fluid level 
must be based on hoop stress data for the resin. The hydrostatic design - basis must be reduced by a service 
factor to determine the actual hydrostatic desig n stress. The maximum service factor shall be 0.5 for wall 
thicknesses less than 9.5 mm. For thicknesses equal to or greater than 9.5 mm, the maximum service factor 
shall be 0.475.  
4.9.5 The radius of the bottom knuckle of a flat -bottom tank shall not be l ess than 25.4 mm for tanks with a 
diameter less than 1.8 m and 38.1 mm for a diameter greater than 1.8 m. The minimum thickness of the radius 
shall not be less than the maximum thickness of the cylinder wall.  
4.9.6 Tank hoop stresses shall be derated for s ervice above 23°C.  
4.9.7 The tolerance indicated in 4.10.3 applies to these dimensions.  
4.10 Dimensions and tolerances  
4.10.1  General  
All dimensions will be taken with the tank in the vertical position, unfilled. Tank dimensions will represent the 
exterior measurement s. 
4.10.2  Outside  diameter  
The tolerance for the outside diameter, including out of roundness, shall be ±3 %.  
4.10.3  Shell wall and head thickness  
The tolerance for average thickness at each elevation shall be − 10 % of the design thickness on the low side 
and shall be unlimited on the high side. The tolerance for individual audit readings shall be limited to − 20 % of 
the design thickness. The total amount of surface area on the low side of the tolerance shall not exceed 10 % 
of the total surface area.  
4.10.4  Placement  of fittings  
4.10.4. 1 The installations of fitting s shall be done by the manufacturer   
4.10.4. 2 The tolerance for fitting placements shall be 12.7 mm in elevation and 2°radial at ambient temperature   
©RSB 2019 - All rights reserved                  8 
 
 5 Quality of finish  
5.1 The internal and external surface of water storage tank shall be smooth, clean and free from other hidden 
internal defects, such as air bubbles, pits and metallic or other material inclusions.  
5.2 The mould parting line near top rim of the tank shall be c ut and finished to the required level. Defects like 
air bubbles and pits at the parting line and at the top of the manhole shall be repaired by hot air filler and rod 
welding method.  
6 Testing  
6.1 Resistance to deformation  
6.1.1 When cylindrical vertical water storage tank is tested in accordance with method 1 described in Annex 
D, the difference between the circumferential measurements shall be not greater than 2 % of the original 
measurements.  
6.1.2 When rectangular loft tank is tested in accordance with metho d 2 described in Annex D, the difference 
between the longitudinal measurements shall be not greater than 3 % of the original measurements.  
6.2 Tensile strength  
The tensile strength at yield shall be determined in accordance with Annex E, and shall be not less  than 12 
N/mm2. 
6.3 Flexural strength  
The flexural strength shall be determined in accordance with ISO 1209 -2. The flexural modulus of the wall of 
the water tank shall be not less than 400 N/mm2. The manufacturer and/or importer of the raw polyethylene 
pellets shall be liable to supply those that can provide the above -described quality.  
6.4 Hydrostatic pressure head  
The Hydrostatic pressure head shall be determined in accordance with Annex F  and t here shall be no leakage 
observed.  
6.5 Routine  test 
The routine tests listed in Table 1 shall be carried out to ensure that satisfactory quality is maintained during a 
production run.  
Table 1 — Routine test parameters  
S/ No  Requirements  Test methods  
i) Resistance to deformation  Annex D  
ii) Hydrostatic pressure head  Annex F  
iii) Carbon black content  Annex A  
iv) Carbon black dispersion  Annex B  
 
             
9                ©RSB 2019  - All rights reserved  
 
 7 Sampling  
7.1 All the water storage tanks of same raw material, same type, size and produced under relatively uniform 
conditions of manufacture shall constitute a lot.  
7.2 Sample size shall be in accordance with Table 1.  
7.3 These tanks shall be selected at random from the lot. In order to ensure randomness of selection, tables 
of random numbers shall be used.  
7.4 Each selected tank, as per Table 1, shall be tested for the requirements in Table 2 below.  
Table 2 — Scale of sampling and criteria for conformity for tanks  
S/N Lot size  Sample size  Acceptance number  
1 Up to 50  1 0 Failure  
2 200 2 0 Failure  
3 300 3 0 Failure  
4 500 5 0 Failure  
5 501 and above  8 1 Failure  
 
8 Marking  
8.1 All the plastic water storage tanks shall be marked with the following information:  
c) manufacturer's name and address;  
d) net capacity, in litres;  
e) lot number and batch number;  
f) country of origin;  
g) manufacturer date;  
h) material code ; and  
i) recyclable  
8.2 The marking shall be carried out either by painting, moulding or by sticking the identification marks on 
external surface of the water tank. The marking shall be permanent.  
9 Transportation  
9.1 Since there are variations in methods of transportation  and handling, the manufacturer’s instructions shall 
be followed in all cases.  
9.2 A suitable means shall be provided, if required, at the open end of open -top tanks to keep the load ed tank 
rigid.  
9.3 All fittings and flange faces shall be protected from damage by covering with suitable plywood, hardboard 
or plastic securely fastened. Tanks shall be positively vented at all times.   
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 9.4 Pipe and tubing, fittings and miscellaneous small parts shall be packaged. Loose items which might 
scratch the interior surface shall not be placed inside the tank during  shipment. Additional protection, such as 
battens, end wrapping, cross bracing, or other interior fastenings shall be used as required t o assure such 
individual equipment pie ces are not damaged in transit.  
9.5 Upon arrival at the destination, the purchaser shall be responsible for inspection for damage in transit. If 
damage has occurred, a claim should be filed with the carrier by the  purchaser. The supplier shall be notified if 
the damage is not first repaired by the fabricator prior to the tank being put into service. The purchaser accepts 
all future responsibility for the effects of the tank failure resulting from damage.  
9.6 Fittings an d accessories that interfere with tank shipment or could be broken during s hipment are shipped 
separately.  
9.7 The supplier shall provide a brochure to the purchaser including information on installation instructions, 
cleaning procedures, disposal and prop er caution and warning signs.  
9.8 The brochure shall be in one of three off icial languages used in Rwanda . 
10 Workmanship  
10.1 The finished tank wall shall be free, as commercially practicable, of visual defects such as foreign 
inclusions, air bubbles, pinholes, pimples, crazing, cracking and delaminations that will impair the serviceability 
of the vessel.   
10.2 All cut edges whe re openings are cut into the tanks shall be trimmed smooth .  
11                ©RSB 2019  - All rights reserved  
 
 Annex  A 
(normative ) 
 
Determination of carbon black content  
A.1 Apparatus  
A.1.1 Combustion boat, made of porcelain or silica, having minimum dimensions of 15 mm length, 9 mm width 
and 8 mm height.  
A.1.2 Combustion tube, made of hard glass of approximately 30 mm diameter and 400 ± 50 mm length.  
A.1.3 Gas flow meter, for measuring and controlling the rate of flow of nitrogen within 1.7 ± 0.3 L/s.  
A.1.4 Thermometer, in the range of 250 °C to 550 °C.  
A.1.5 Furnace, to accommodate the combustion tube to give temperatures up to at least 500 °C.  
A.2 Reagents  
A.2.1 Nitrogen, as technical grade.  
A.2.2 Trichloroethylene  
A.3 Procedure  
A.3.1 Assemble the apparatus as shown in Figure 3. Both cold traps following the combustion  tube shall 
contain trichloroethylene, but only the first need be cooled with solid carbon dioxide.  Alternatively, the entire 
apparatus may be placed in a fume hood and the two traps following the combustion tube omitted.  Fill the dry 
tube with anhydrous  CaCl2 or other suitable desiccant. Hold between loose plugs of glass wool.  
A.3.2 Heat a clean combustion boat to red heat in a Bunsen flame; then transfer the boat to the desiccant 
and allow it to cool over fresh desiccant. Hold between loose plugs of gla ss wool.  
A.3.3 Remove the boat from the desiccant and weigh it to the nearest 0.000 1 g. Immediately place 1.0 ± 0.1 
g of the ethylene plastic under test in the boat and quickly weigh to the nearest 0.000 1 g.  
A.3.4 Heat the furnace to a constant temperature of 600 °C. Adjust the rate of nitrogen flow to 1.7 ± 0.3 L/min. 
Open the inlet end of the 2.9 -cm di ameter tube, quickly place the combustion boat with the sample into the tube 
at the centre of the furnace, and adjust the thermocouple so that th e weld is touching the boat. Insert copper 
plug, if this is used. Quickly close the furnace and allow heating to proceed for at least 15 min.  
A.3.5 Move the tube or furnace so that the boat is no longer in the heated zone of the furnace and allow 5 
min for  cooling, while maintaining the flow of nitrogen. Remove the copper plug, if present and the boat through 
the inlet end of the tube and allow it to cool for at least 30 min. Take care that the boat does not become 
contaminated from any deposits on the wall s of the tube. Then quickly reweigh the boat and its contents to the 
nearest 0.000 1 g.  
A.3.6 Make all determinations in duplicate.  
A.4 Calculation  
Carbon black content, % by weight W= 𝑊𝑠
𝑊𝑟𝑥100  
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 where  
Wr   the mass, in g, of the boat before heating in air;   
Ws   the mass, in g, of the boat after heating in air; and  
W  the mass, in g, of the material taken for the test.  
 
Figure 4 — Assembly of apparatus for carbon black determination  
 
 
 
 
13                ©RSB 2019  - All rights reserved  
 
 Annex  B 
(normative ) 
 
Determination of carbon black dispersion in polyethylene materials  
B.1 Procedure  
B.1.1  Place two clean microscope slides on a hot plate maintained at 170 °C to 210 °C. Place three specimens 
of pin -head size, each weighing about 5 mg, and each one cut from a separate granule, on one of the hot 
microscope slides, about 20 mm apart. Place a piece of metal shim 40 -mm long, 20 -mm wide and 0.03 mm 
thick at each end and cover the whole with the other hot microscope slide. Press the specimens by applying 
even pressure for 11/2 to 2 minutes, to the whole area of the face of the upper slide. After the specimens have 
been placed on the slides, these shall not remain on the hot plate for more than 3 minutes.  
B.1.2  When the slides are cool enough to be handled examine the three specimens through a micros cope at 
magnification of 200 ± 10 with a field of view of 10.1 mm diameter. Note shall also be made of any lack of 
uniformity of the background.  
B.2 Reporting  
The carbon black dispersion in the material under test shall be considered to be satisfactory, if the  specimens 
show a uniform background free from white streaks.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
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 Annex  C 
(normative ) 
 
Determination of effect of heavy metals on water quality  
C.1 Method of extraction  
C.1.1  Three test specimens of approximately 500 mm2 in surface area shall be taken from tank.  
C.1.2  Each test specimen shall be pre -washed for a period of 6 hours using tap water with pH of 7 to 8. The 
water shall be passed through the specimen at a velocity of 50 mm/s while the specimen is kept fully immersed 
with water. After was hing, the specimen shall be filled with fresh solution of the distilled water acidified to pH of 
4.5 ± 0.1 by bubbling a current of carbon dioxide through it, and both ends sealed with a material that does not 
contain any toxic substances nor interfere wit h the determinations of such constituents in the aqueous samples.  
C.1.3 After maintaining the specimens at room temperature for 48 hours, the solution shall be decanted into 
a suitable container for analysis as the first extraction.  
C.1.4 The procedure sha ll be repeated a second and a third time. Retain these samples for the determination 
of the amount of metals and other toxic substances a s second and third extractions.  
C.1.5 The first extraction and the third extraction shall be analyzed for lead.  
C.1.6 The third extraction shall also be analyzed for dial kyl tin (C4 and above) as tin.  
C.1.7  When calcium and mercury are present; all three extracts shall be analyzed.  
C.2 Method of analysis  
Analysis for lead, tin, cadmium and mercury shall be carried out using a tomic absorption.    
15                ©RSB 2019  - All rights reserved  
 
 Annex  D 
(normative ) 
 
Determination of Resistance to Deformation test  
D.1 Method 1 for cylindrical vertical tank  
D.1.1  The water tank shall be placed on a flat level base. A circumferential measurement shall be made 
parallel to the base at a distance of one third the effective height from the bottom. The tank shall be filled up to 
the effective height at a minimum rate of 23 L/min with water at temperature of not less than 15 °C.  
D.1.2  A continuous film of polyethylene shall be floated over th e whole of the surface of water in tank to 
prevent evaporation.  
D.1.3  The temperature of the tank and water shall be maintained at a temperature not less than 15 °C and 
after 7 days a circumferential measurement shall be made at level referred at level to in D.1.1. The difference 
between the two circumferential measurements shall be expressed as a percentage of the original 
circumferential measurement.  
D.2 Method 2 for rectangular loft tank  
D.2.1  The rectangular tank shall be placed on a level base. The interna l length and width of the tank shall be 
measured on the centrelines, as shown in Figure 5 at the centre of effective height.  
 
 
Figure 5— Centreline measurements  
D.2.2 The tank shall be filled up to the effective height at a minimu m rate of 23 L/min with water at a 
temperature not less than 15 °C. The lid shall close after filling the loft tank.  
D.2.3 The temperature of the tank and water shall be maintained at not less than 15 °C and after 7 days 
measurements of length and width shall be made at previously determined centrelines.  
  
 
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 D.2.4 The deformation in each direction shall be calculated as follows:  
100x 212 1
LLW WD
 
100x 2 11 2
WWLLD
 
 
Where:  
DL   = the deformation of the longer side  
DW   = the deformation of the shorter side  
W1 = the width at the start of the test  
W2 = the width at the end of test  
L1   = the length at the start of the test  
L2 = the length at the end of test   
17                ©RSB 2019  - All rights reserved  
 
 Annex  E 
(normative ) 
 
Determination of tensile properties  
E.1 Apparatus  
E.1.1 Testing machine, with gr ips that can be separated at one or more (as required) of the rates given in E.5.  
E.1.1.1 Grips, for holding the test specimen, one being attached to a fixed or essentially stationary member 
of the machine and the other to a movable member. The grips are s elf-aligning; that is, they are attached to the 
fixed and movable member respectively in such a manner that they will move freely into alignment as soon as 
any load is applied, so that the long axis of the test specimen will coincide with the direction of the applied force 
through the centre line of the grip assembly. The test specimen is held in such a way that slip relative to the 
grips is prevented as far as possible.  
E.1.1.2 Load indicator, suitable load -indicating mechanism capable of showing the total  tensile force carried 
by the test specimen when held by the grips.  
This mechanism is essentially free from inertia lag at the specified rate of testing and indicates the force with 
an accuracy of ± 1 % of the indicated value.  
E.1.2 Extension indicator (when required), suitable instruments for determining, at any time the test, the 
distance between two fixed points of reference lines located within the middle parallel -sided pan of the test 
specimen. It is desirable, but not essential,  that this instrument shall automatically record this distance (or any 
change in it) as a function of the force on the test specimen or of the elapsed time from the start of the test, or 
both. If only distance as, function of elapsed time is recorded, forc e-time data are also taken. The instrument is 
essentially free of inertia lag at the specified speed of testing and is accurate to ± 1 % of strain or better.  
The elongations between the reference lines at yield and at break of flexible plastics are measure d to the nearest 
7 mm by any convenient means. For the measurement of modulus of elasticity the instrument is capable of 
measuring the distance between the reference lines to an accuracy of ± 1 mm.  
E.1.3 Micrometers, dial -gauge micrometer, reading to at le ast 0.02 mm and provided with a flat circular foot 
that will apply a pressure of 9.81 x 10 -3 to 29.43 x 10 -3 N/mm2. To the test specimen, for measuring the 
thickness of test specimens of non -rigid materials.  
E.2 Test specimens  
E.2.1 The test specimen is cut fr om the obtained flat portion of the top of the bank with the knife -edged die.  
Reference lines, if used, are 25 ± 1 mm apart and are equidistant from the ends of the middle parallel -sided part 
of the test specimen as shown in Figure 5.  
E.2.2 It is necessary to apply reference lines to the test specimens. This is done with ink or other medium that 
will not affect the material being tested. Reference lines are not scratched, punched or impressed, upon the test 
specimen.  
E.3 Number of test specimens  
E.3.1 At least five test specimens are tested for each tank.  
E.3.2 Test specimens that do not break with parallel portion are discarded and further test specimens are 
tested.   
©RSB 2019 - All rights reserved                  18 
 
 E.4 Speed of testing  
E.4.1 The speed of testing is the rate of separation of grips of the t esting machine during the test.  
E.4.2 The speed of testing is preferably chosen from one of the following, but in any' case is determined by 
the specification for the material being tested, or by agreement between those concerned (see also E.5.2.1):  
E.4.2.1 With some types of testing machines the rates of separation of grips are virtually the same irrespective 
of whether the machine is running, idle or under load. With these machines, a ratio of separation of grips under 
load within the above tolerances can  be obtained by setting the speed of the machine when it is idle.  
E.4.3 If elastic modulus in tension is being determined, the preferred speed of testing is speed A or as is 
specified. Elastic modulus determinations are made with separate test specimens f rom those used to determine 
tensile strength and elongation whenever the speeds of testing are not the same.  
E.5 Procedure  
E.5.1 Measure the thickness of test specimens at several points to the nearest 1 % with the dial -gauge 
micrometer described in E.2.3. The  width is taken to be the width measured to the nearest 0.05 mm of the 
middle parallel -sided part of the cutter shown in Figure 8.  
E.5.2 Place the test specimen in the grips of die testing machine, taking care to align the long axis of the test 
specimen an d the grips with an imaginary line joining the points of attachment of the grips to the machine. 
Tighten the grips evenly and firmly to a degree necessary to prevent the test specimen from slipping during the 
test but not the point where the specimen shall  be crushed.  
E.5.3 For the determination of properties other than modulus of elasticity and for all test specimens set the 
speed of testing at the specified value and start the machine.  
E.5.3.1 For the test specimens, some or all of, the following shall b e noted as required by the specification 
for the material:  
a) load at the yield point (see Note 1);  
b) distance between the reference lines at the yield point;  
c) load at break or the maximum load (see Note 2); and 
d) distance between the reference lines at break.  
E.5.3.2 The above information can be obtained from an autographically recorded stress¬ -strain curve or 
may be directly observed.  
NOTE 1  In cases where the yield point is not well defined, it is frequently necessary to define an offset yield point. This 
is do ne by specifying a point on the load/extension curve where the curve departs from linearity by a specified percentage 
elongation or extension (see Figure 10).  
NOTE 2  When  testing specimens whose cross -sectional area decreases considerably before break, the  force may 
decrease to some extent after having reached a maximum value, so that the maximum force and the force at break are not 
the same. For such test specimens the force at break cannot be obtained by the use of testing machines that only register 
the maximum force. It is often difficult for the load to be read of the moment of break with sufficient accuracy; it is therefore  
recommended that the load at break be determined from a force/ extension diagram obtained from a tensile testing machine 
equipped with a recording mechanism.  
E.6 Calculation and expression of results  
E.6.1  The force at yield or the maximum force, or the force at break, as appropriate, is divided by the, original 
minimum cross -sectional area of the test specimen in square centimetres. The  results are expressed in N/mm2.  
19                ©RSB 2019  - All rights reserved  
 
 E.6.2  The extension at the yield point (see Figure 9) or the extension at the moment at break, as appropriate, 
is divided by the original distance between the reference lines and multiplied by 100. The elongation at yield o r 
break is reported to two significant figures.  
E.6.3  The elastic modulus is calculated from the initial linear portion of the force Vs extension curve, (see 
Figure 10) by dividing the difference in stress corresponding to a section of the straight -line by  the corresponding 
difference in strain. For this purpose, the difference in stresses is the difference in force divided by the original 
cross -sectional area of the specimen in square centimetres and the difference in strain is the difference in 
extension divided by the original distance between the fixed points used for the measurement of extension 
under force.  
E.6.4  For all five specimens, the arithmetic mean of all values is calculated to three significant figures (except 
for elongation for which the mea n is calculated to two significant figures) and reported as the "average value" 
for the particular property in question.  
E.6.5  If the standard deviation (estimated) is required, it is calculated as follows and is reported to two 
significant figures:  
     1/nxnx S2- 2
 
Where:  
S = the estimated standard deviation;  
x   = the value of single observation;  
n   = the number of observations;  
x
 = the arithmetic mean of the set of observations.  
E.7 Test report  
The test report shall include the  following as appropriate:  
a) manufacturer’s principle dimensions, etc.;  
b) width and thickness of parallel portions;  
c) method of preparation of test specimen;  
d) conditioning procedures used;  
e) atmospheric conditions in test room;  
f) number of test specimen;  
g) speed of tes ting; 
h) tensile stress at maximum force or at break, or both average values;  
i) elongation at yield or at break, or both average values;  
j) elastic modulus, average value;  
k) standard deviations of the individual test results; and  
l) date of test.   
©RSB 2019 - All rights reserved                  20 
 
 Dimensions in millimetres  
Figure 6 — Type 1 test specimen showing positions of reference lines (if used) . Tolerance on 
dimensions: ± 5 %  
 
Where:  
 A is the o verall length, minimum   110 
 B is width at ends     20 ± 0.5  
 C is the l ength of narrow parallel portion  60 ± 0.5  
 D is width of narrow parallel portion  10 ± 0.5  
 E is the r adius, minimum    60 
 F is the t hickness     See text  
 G is the d istance between reference lines  50 ± 0.5  
 H is the i nitial distance between grips   115 ± 5  
  
 
 
21                ©RSB 2019  - All rights reserved  
 
 Dimensions in  millimetres  
Tolerance on dimensions ± 5 %     
Figure 7 — Cutting edges of die -type 2 test specimen showing positions of reference lines (if used)  
 
Where  
A is the o verall length     115 
B is the w idth at ends     25 ± 1  
C is the l ength of narrow parallel portion  33 ± 2  
D is the w idth of narrow parallel portion  6 + 0.4  
F is the s mall radius     14 ± 1  
J is the l arge radius     25 ± 2  
K is the d istance between reference lines  25 ± 1  
L is the i nitial distance between grips   80 ± 5  
M is the thickness     See text  
  
 
 
©RSB 2019 - All rights reserved                  22 
 
 Dimensions in millimetres  
Tolerance on dimensions ± 5 %     
Figure 8 —Type 3 test specimen  
 
Where  
A is the o verall length     110 
 B is the w idth at ends     45 
 C is the t hickness at ends    6.5 
 D is the length of narrow parallel portion  9.5 
 E is the w idth of narrow parallel portion  25 
 F is the t hickness of narrow portion   3.2 
 G is the s ide radius     75 
 H is the face radius     75 
 J is the e nd radius     6.5 
  
 
23                ©RSB 2019  - All rights reserved  
 
 Dimensions in millimetres  
 
 
Figure 9 — Grip for type 3 test specimen  
Tolerance on dimensions ± 5 %  
 
 
Figure 10 — Load/Extension diagram  
Where:  
(a) is the  material for which a yield point can be determined; and  
(b) is the  material for which an offset yield point ha d to be determined .  
 
 
 
©RSB 2019 - All rights reserved                  24 
 
 Annex  F 
(normative ) 
 
Determination of Hydrostatic pressure head  
F.1 The tank shall be filled with water up to the nominal capacity.  
F.2 Thereafter it shall be fitted with a pump with a pressure gau ge.  
F.3 The pump shall then be started and run till the nominal pressure level is attained and examined for leaks.  
F.4 There shall be no leakage observed.  
 
 
  
25                ©RSB 2019  - All rights reserved  
 
 Annex  G 
(informative ) 
 
Recommendations for installation and fittings of tanks  
G.1 Tank installation  
G.1.1 Vent pipe/overflow pipe is provided near  the top  with mosquito  and insect  proof  cap  
G.1.2 The flat base of cylindrical vertical or rectangular water storage tanks should be fully supported over its 
whole bottom area by a durable rigid, flat and level platform sufficiently strong to withstand without deflection 
the weight of the tank when filled fully with the water. In case, the tank is placed on a suitable M. S. platform 
then it is essential that the latter is free from sharp edges, corners or surface  projections and shall be corrosion 
resistant.  
NOTE  The requirements for the construction of the reinforced cement concrete or pre -cast cement concrete depend 
on the capacity of the tank and location . Civil engineering will establish the viability of the g eology that the water tank will be 
placed on and this will dictate site preparation and cost . The choice of materials of construction will be impacted by the 
whether the tank is located indoors, outdoors or underground.  
G.1.3 Where required the tanks shall  be suitably anchored. The tanks may also be provided with clamping 
devices.  
G.1.4 the pipelines, valves and other fittings should be supported in such a manner that it is aligned properly 
so as not to produce any distortion in the water tank where the fit ting is fixed.  
G.1.5 the check nuts of the threaded connection should be placed after placing rubber gaskets and should 
not be over tightened. Under no circumstances should jointing compounds or putty be employed in contact with 
the Polyethylene water tank s. PTFE  (poly -tetra-tluroethylene) unsintered tape may be wrapped around the 
threaded  Portion of the valves and connections to act as a sealant  
G.1.6 Circular holes drilled for fixing threaded connections should have a clean edge free from notches.  Holes 
can be drilled with a high speed steel hole saw cutter. Scratching or scoring the wall should  not be done for 
setting out holes.  
G.1.7 where the section of water tank has a change in profile which is accomplished with a radius, it is  
essential that the outer extremities of the threaded connections are clear of this radius.  
G.1.8 the water storage tank should not be installed in close proximity to heaters or other direct sources of 
heat.  
G.2 Fittings  
G.2.1 for providing inlet, outlet and other connections. Usually full threaded G.I. brass connections are used 
which  shall not produce any kind of ha rmful effect on potable water. Flat Surface may preferably be provided to 
fix outlet pipes at appropriate locations.  The different sizes of threaded connections  required to be fixed for 
different capacities of water storage tanks may be according to Table H.1. 
G.2.2 The overflow pipes should be provided with non -corrodible mosquito -proof device of Maximum 
clearance not more than 1.6 mm  
 
  
©RSB 2019 - All rights reserved                  26 
 
 Table G.1 Sizes of threaded connections  
 
S/No  Capacity of water storage tank  Nominal bore size of 
threaded connection  
1 Up to 750 12.5 
2 Above 750 and up to 2 000  25 
3 Above 2 000  and up to 4 000  40 
4 Above  4000  and up to  10000 50 
5 Above  10000  75 
 
 
 
 
 
 
 
 
 
 DRS 128: 2019  
ICS 23.020.10  
 
©RSB 2019  - All right s reserved