ICS 77.140.01  
 
Reference number  
DRS 506: 2022  
© RSB 2022  
  
 RWANDA 
STANDARD  DRS 
506  
 
First edition  
2022 -mm-dd 
Rectangular pressed steel tanks — 
Specification  
   
DRS 506: 2022  
©RSB 2022  - 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 2022  
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 reproduce 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.r w 
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 506: 2022  
iii                ©RSB 2022  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................  iv 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Types  ................................ ................................ ................................ ................................ .............  2 
5 General requirements  ................................ ................................ ................................ ..................  2 
6 Materials  ................................ ................................ ................................ ................................ ........  3 
7 Dimensions  ................................ ................................ ................................ ................................ ... 3 
8 Fabrication  ................................ ................................ ................................ ................................ .. 10 
9 Erection  ................................ ................................ ................................ ................................ ....... 14 
10 Test ................................ ................................ ................................ ................................ ..............  15 
11 Inspection  ................................ ................................ ................................ ................................ .... 16 
12 Packing  ................................ ................................ ................................ ................................ ........  16 
13 Marking  ................................ ................................ ................................ ................................ ........  16 
14 Order information  ................................ ................................ ................................ .......................  16 
Annex  A (normative)  Information to be supplied with the enquiry and order  ................................ . 16 
A.1 The following details should be supplied by the purchaser at the time of enquiry and 
order:  ................................ ................................ ................................  Error! Bookmark not defined.  
 DRS 506: 2022  
©RSB 2022  - All rights reserved                  iv 
 Foreword  
Rwanda Stan dards are prepared  by Technical Committees and approved by Rwanda 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 506 was prepared by Technical Committee RSB/TC 047, Steel, aluminium and related products . 
In the preparation of this standard, reference was made to the following document : 
1) IS 804:1967 , Specification for Rectangular Pressed Steel Tanks  
The assistance de rived from the above source is hereby acknowledged with thanks.  
Committee membership  
The foll owing organizations were represented on the Technical Committee on Steel, aluminium and related 
products  (RSB/TC 047) in the preparation of this standard.  
Chillington Rwanda Ltd  
City of Kigali  
Eastern Hope Ltd  
Herocean Ltd  
Integrated Polytechnic Regional Centre (IPRC) — Kigali  
Kabuye Sugar Works Ltd  
Kamuru Trading Company Ltd  
Madras Material Ltd  
MANUMETAL Ltd  
Ministry of Environment  
Real Contractors Ltd  
Roofing Ltd  DRS 506: 2022  
v                ©RSB 2022  - All rights reserved  
 Rwanda Consumer’s Rights Protection Organization (ADECOR)  
Rwanda Environment Management Authority (REMA)  
Rwanda Housing Authority (RHA)  
Rwanda Transport Development Authority (RTDA)  
Standards for Sustainability (SfS)  
University of Rwanda —College of Science and Technology (UR -CST)  
Rwanda Standards Board (RSB) – Secretari at 
  DRS 506: 2022  
1                ©RSB 2022  - All rights reserved  
 Rectangular pressed steel tanks — Specification  
1 Scope  
1.1 This Draft Rwanda Standard specifies requirements , sampling and test methods  for materials, fabrication , 
erection and supply of rectangular pressed steel tanks used for the storage of cold  water,  hot water and certain 
other liquids u nder pressure not greater than the static head corresponding to the depth of the tank.  
1.2 This Draft Rwanda Standard does not cover the requirements of tanks storing liquids having temperature s 
higher than 100 °C, or those tanks subject to earth or other external pressures besides wind pressure.  
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 appli es. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
RS ISO 3573, Hot-rolled carbon steel sheet of commercial and drawing qualities  
RS ISO 630 Structural steels  
RS ISO 4016 Hexagon head bolts — Product grade C  
RS ISO 4018 Hexagon head screws — Product grade C  
RS ISO 14344 Welding consumables — Procurement of filler materials and fluxes  
3 Terms and definitions  
For the purposes of this standard, the  following  terms and definitions the apply.  
3.1 
liquid  
substance which is in liquid state at atmospheric pressure  
 Note  1 to entry : Example of a liquid: kerosene, diesel fuel and water.  
3.2 
cold water or cold liquid  
water or liquid at a temperature not exceeding 40  °C  
©RSB 2022  - All rights reserved                  2 
 3.3 
hot water or cold liquid  
water or liquid at a temperature above 40  °C, but not exceeding 100  °C 
4 Types  
4.1 Pressed steel tanks shall be classified into the following three types:  
a) type 1 : Tanks with all flanges external (see Figure 1)  
b) type 2 : Tanks with all flanges internal  
c) type 3 : Tanks with bottom flanges internal and side flanges external  
4.2 Each of the above types may be either with open top or with covered top . 
5 General requirements   
5.1 Pressed steel tanks are not recommended for depths greater than 5 m . 
5.2 Type 1 tanks are nor mally used where a plain internal surface is necessary or where there are no restrictions 
as to external access or where the exterior of the tank is to be lagged.  
5.3 Type 2 tan ks are normally used at a location where access to the exterior  for erection is precluded due to 
insuf ficient  space inside a building.  
5.4 Type 2 and 3 tanks are suitable for use where they are to be erected on a solid level floor.  DRS 506: 2022  
3                ©RSB 2022  - All rights reserved  
  
NOTE 1 For tanks of 2.5 m and less length and width, the stays may be horizontal from end to end and/or side to side.  
NOTE 2 This figure is diagrammatic, and illustrative only and does not purport to represent any particular design.  
Figure 1 — Typical pressed steel sectional rectangular tank with external flanges  
6 Materials  
6.1 Mild steel plate and com ponents used in pressed steel tanks shall  be in accordance with  RS ISO 630 . Mild 
steel sheets used in the manufacture of  pressed tanks shall be in accordance with  RS ISO 3573.  
6.2 Bolts and nuts used shall be of mild steel. They shall be hexagonal and finished black in accordance with  
RS ISO 4016  and RS ISO 4018 . 
6.3 Joint material  
6.3.1  The material used for jointing shall  be insoluble in the liquid to be stored and shall be capable of 
withstanding the temperature variation in the liquid to be stored in the tank ( refer to  3.2). It shall be of a suitable 
type depending upon the purpose for which the tank is to be used and sh all be as agreed to between the 
purchaser and the manufacturer.  
6.3.2 Electrodes used for welding shall be in accordance with  RS ISO 14344 . 
7 Dimensions   
7.1 The nominal size of unit plate shall be 1·25 m2, the actual overall dimensions depending upon the particular 
manufacturer of the plates . The size of tanks shall be specified as multiples of the nominal dimensions of 1.25 
 
©RSB 2022  - All rights reserved                  4 
 m. The nominal capacity shall be based upon the nominal dimensions of the tank, for example, 1.25 x 1.25 x 
1.25 m equals 1950 L. 
7.2 Pressed mild steel tanks shall be either 1.25 m, 2.50 m, 3.75 m or 5.00 m deep. Typical sizes, approximate 
weights and nominal capacity of Type I tanks with open tops for the depths mentioned above are given 
respectively in Tables 1, 2, 3 and 4.  
7.3 The minimum nominal thickness of plates used for different depths of tanks used for storage of cold liquids 
with specific gravity not exceeding 1.0 shall be as given in Table 5.  
7.3.1  In the case of hot liquids with specific gravity not exceeding 1.0, the th ickness of plates for different depths 
of tanks shall be in accordance with Table 5 except that no plate of the tank shall be less than 6.0 mm thick.   
Table 1 — Typical sizes, approximate weight and nominal capacities of tanks with external flanges for 
“tanks 1.25 metres deep, plate 5.0 mm thick throughout ” 
 
𝑵𝒐𝒎𝒊𝒏𝒂𝒍  𝒔𝒊𝒛𝒆
𝑳𝒆𝒏𝒈𝒕𝒉  ×𝑩𝒓𝒆𝒂𝒅𝒕𝒉
𝒎 × 𝒎 
 Plates in 
tanks 
number  Nominal 
capacity  
 
 
L Approximate 
total weight 
empty  
 
kg 𝑨𝒑𝒑𝒓𝒐𝒙𝒊𝒎𝒂𝒕𝒆  𝒐𝒖𝒕𝒔𝒊𝒅𝒆  𝒅𝒊𝒎𝒆𝒏𝒔𝒊𝒐𝒏𝒔 ,𝒎 
𝑳𝒆𝒏𝒈𝒕𝒉   𝑩𝒓𝒆𝒂𝒅𝒕𝒉   𝑫𝒆𝒑𝒕𝒉 
 
1.25 × 1.25* 5 1 950  400 1.40 1.40 1.33 
2.50 × 1.25  8 3 900  700 2.65 1.40 1.33 
3.75 × 1.25  11 5 850  900 3.90 1.40 1.33 
5.00 × 1.25  14 7 800  1 200 5.15 1.40 1.33 
2.50 × 2.50  12 7 800  1 000  2.65 2.65 1.33 
3.75 × 2.50  16 11 700  1 350  3.90 2.65 1.33 
5.00 × 2.50  20 15 600  1 650  5.15 2.65 1.33 
6.25 × 2.50  24 19 500  2 050  2.65 2.65 1.33 
3.75 × 3.75  21 17 550  1 750  3.90 3.90 1.33 
5.00 × 3.75  26 23 400  2 200  5.15 3.90 1.33 
6.25 × 9.75 31 29 950  2 600  6.40 3.90 1.33 
7.50 × 3.75 36 35 100  3 050  7.65 3.90 1.33 
8.75 × 3.75 41 40 950  3 500  8.90 3.90 1.33 
5.00 × 5.00 32 31 200  2 700  5.15 5.15 1.33 
6.25 × 5.00 38 39 000  3 200  6.40 5.15 1.33 
7.50 × 5.00 44 46 800  2 700  7.65 5.15 1.33 
8.75 × 5.00 50 54 600  4 250  8.90 5.15 1.33 
10.00 × 5.00 56 62 400  4 800  10.15  5.15 1.33 
6.25 × 6.25 45 48 750  3 800  6.40 6.40 1.33 
7.50 × 6.25 52 58 500  4 400  7.65 6.40 1.33 DRS 506: 2022  
5                ©RSB 2022  - All rights reserved  
 7.50 × 7.50 60 70 200  4 950  7.65 7.65 1.33 
8.75 × 8.75 77 95 550  6 450  8.90 8.90 1.33 
*Thickness of sheets for this tank only is 3.15 mm throughout  
 
 
 
*Thickness of sheets for this tank only is 3.15 mm throughout  
NOTE The capacity of tank with joints as in Figure 2 will have proportionate reduction in capacity.  
 
©RSB 2022  - All rights reserved                  6 
 Table 2 —  Typical sizes, approximate weight and nominal capacities of tanks with external flanges 
“fanks 2.50 metres deep, plates 5.0 mm and 6.0 mm thick”  
 
DRS 506: 2022  
7                ©RSB 2022  - All rights reserved  
 Table 3 — Typical sizes, approximate weight and nominal capacities of tanks with external flanges for 
“tanks 3.75 metres deep, plates 5.0 mm and 6.0 mm thick”  
 
 
©RSB 2022  - All rights reserved                  8 
 Table 4 — Typical sizes, approximate weight and nominal capacities of tanks with  external flanges for 
"tanks 5 metres deep, plates 5.0 mm, 6.0 mm and 8.0 mm thick".  
 
DRS 506: 2022  
9                ©RSB 2022  - All rights reserved  
 Table 5 — Minimum nominal thickness of plates  
 
Table  1.1 Amendment to Table 1  —  Replace the values for Aproximate total weight empty ( kg) by th e 
values stated below.  
 
7.3.2 For cold or hot liquids with specific gravity greater than 1 -0, the thickness of plates shall be as agreed to 
between the purchaser and the manufacturer.  
 
©RSB 2022  - All rights reserved                  10 
 8 Fabrication  
8.1 The plates shall be heated unifo mly in a furnace and formed in a press, each of which shall be capable of 
taking the whole plate at one time. Alternatively, the plates may be pressed cold, the flanges made by V die and 
the comers welded provided no cracks develop. Re -drawing of plates to bring the same to the specified 
dimensions shal l not be permitted.  
8.2 The flanges of the plates shall be pressed square or partly square and partly at an angle of 45 ° to the face 
of the plate or all 45° to the face of the plate (refer to Figure 2, 3 and 4).  
8.3 All steel plates, ba rs and stays shall b e carefully levelled and straightened according to the approved 
methods including  hammering before and after they are being punched or drilled if considered necessary by the 
inspector. The width of the flanges shall be su itable for the connecting bolts use d. 
8.4 They shall have holes accurately drilled or punched in jigs so that the bolt holes are alignable and 
interchangeable with those of any other matching flange. The spacing of the bolt holes in the flanges shall not 
exceed 80 mm. For 1.25 m cubic tanks , the diameter of bolts should be 12 mm, except for the roof where it may 
be up to 10 mm diameter (alternatively 8 mm with the maximum spacing of 55 mm including for the roof).  
8.5 For other tanks, the diameter of bolts should normally be 14 mm or over, ex cept at the roof where it may be 
up to 12 mm.  
8.6 If any other arrangement for the size of flange, diameter of the bolt and spacing of the bolt is desirable, 
these shall be as agreed to between the purchaser and the manufacturer. Wh erever necessary, the flange bolt 
should be fitted with washers under nut.  
 
Figure 2 — Flange joints (partly squared)  
DRS 506: 2022  
11                ©RSB 2022  - All rights reserved  
  
Figure 3 — Flange joints (squared)  
 
Figure 4 — Corner details  
8.7 The sides of tanks shall be supported by stays at the junction of two or more plates; the stays shall be made 
from mild steel rolled sections. They shall be attached to the plates by bolting to the flanges or by mild steel 
cleats of strength equal to that  of stays bolted to the tank plates. The stays shall connect sides to bottom, and/or 
horizontally sides to sides generally in accordance with Figure 1.  
8.8 All outside edges of gussets shall be cut  neatly and accurately and the edges ground where necessary . All 
burrs left by the drill and the sharp edges of all bolt hole, shall be completely removed. All steel work intended 
to be riveted or bolted shall be completely in contact over the entire surface.  
8.9 All parts of steel tanks shall be coated with paint  conforming to  relevant  approved standards and the paint 
shall be suitable for storage of the liquid for which the tank is intended . 
8.10 Pads for connection, tapped bosses, screwed flanges or sockets, as may be required by the purchaser, 
shall be welded t o the inside or outside or bolted to the tank plate. Pads shall be seal welded and drilled and/or 
tapped to suit flanges . 
 
©RSB 2022  - All rights reserved                  12 
 Single pads shall be provided for connections on one side of the plate and double pads for connection on both 
sides of the plate. Tapp ed sockets shall be in accordance with the requirements of relevant approved standards . 
Where possible, connections shall be so positioned so as to avoid the embossment of the plate (see. Fig. 5 to 
9). When double connections are to be provided in the pads , the studs shall be staggered on opposite faces.  
8.11 Inlet pipes and the overflow pipe, if arranged through the bottom of the tank only, shall be of bell mouth 
type.   
8.12 Where connections are welded to the tank as well as where the corners are welded, the welding shall be 
done by the metal arc process. The plates and connections shall be prepared with care, and fusion faces shall 
be reasonably free from rust, paint or other foreign matter. Where the plates are cut, edges shall be dressed 
smooth. Pads sh all be in fair contact with the plates before the welding is resorted to. All welds should be made 
in the down hand position. The size of the welds shall conform to those shown in Fig. 5 to 9.  The surfaces of 
the welds shall be even, free from cracks or bl ow holes. The welds shall be completely fused to the parent metal 
without undercut.  
 
Figure 5 — Tapped socket or boss welded into tank plate  
 
Figure 6 — Screwed flange welded to tank plate  
 
Figure 7 — Single pad welded to tank plate  
DRS 506: 2022  
13                ©RSB 2022  - All rights reserved  
  
Figure 8 — Double pad welded to tank plate (pads for 50 mm pip and under, sealing welds omitted)  
 
Figure 9 — Thick pad welded to tank plate  
8.12 Tanks that are 2.5 m deep or more shall be provided with a mild steel internal access ladder of minimum 
width of 40 cm. In the case of covered tanks, the ladder shall be adjacent to the manhole.  
8.13 Coverings   
8.13.1 In the case of covered  top tanks, the coverings may be of the following types:  
a) Mild steel plate shall be in accordance with  RS ISO 630  and mild steel shall be in accordance with  RS ISO 
3573 ; and 
b) Galvanized sheets shall be in accordance with RS EAS 11.  
8.13. 2 Asbestos sheets shall never be permitted for use.  
NOTE 1  Mild steel cover plates shall be 3.15 mm thick.  
NOTE 2  The design and construction of the cover shall be such that the rain water can d rain off easily.  
 
©RSB 2022  - All rights reserved                  14 
 8.13. 3 In all cases, covered top tanks shall be provided with a manhole of diameter not less than 450 mm if 
circular, or 450 x 450 mm if square, to give access to the inside of the tank. In the case of covered top tanks 
there shall be no o pening at the junction of the top cover with the sides which will allow mosquitoes inside the 
tank.  
8.13. 4 In the case of covered top tanks, there shall be no opening at the junction of the top cover with the sides 
which will allow mosquitoes inside the ta nk. Vent pipes may be provided, if required by the purchaser. The 
vertical vent pipe, if necessary, shall be provided on top with a flanged bend, the mouth of the bend being fitted 
with a mosquito proof netting.  
8.13. 5 Covering of tanks shall be adequately  supported by rolled steel or pressed steel bearers or trusses. If 
the top cover acts as an effective tie, the top horizontal stays may be omitted.  
9 Workma nship 
The workmanship shall be of the highest order and the finished tanks shall be free from all defects of 
manufacture. Accuracy shall be observed in the design, manufacture and erection of every part of the tank. All 
similar parts shall be strictly interchangeable. All joints shall be leak -proof and the edges of flanges finished 
flush with each othe r. 
10 Erection  
10.10 The tanks shall be erected in accordance with the detailed drawings and manufacturer's instructions.  
10.11 Where tank with external flanges is to be erected at ground level, adequate working space for erection is 
required all round; underneath and above the finished size of the tank.  
10.12 All tanks shall be effectively supported under each transverse joint and both ends of the tanks. This may 
be by the following:  
a) rolled steel joists forming beams and architraves mounted on dwarf pillars (refer to Figure 10). Joists 
shall be designed to carry the imposed load with a maximum deflection of one part in one five -hundredth 
of the span ; and  
b) dwarf walls  of brick or concrete with footings to suit the depth of tank and the nature of ground. Dwarf 
walls for 3.75 m of 5 m deep tanks sha ll have a mild steel capping plate to  provide a bearing surface 
on the wall ( Refer to Figure 11). 
10.13 After erection, the tank shall be finished with two coats of suitable anti -corrosive paint mutually agreed to 
between the manufacturer and the purchaser.  DRS 506: 2022  
15                ©RSB 2022  - All rights reserved  
  
Figure 10  — Rolled steel joist supports for pressed steel tanks  
 
Figure 11 — Dwarf wall supports for pressed steel tanks  
11 Test 
Each tank shall be tested at site after erection for leakage under full static head.  
 
©RSB 2022  - All rights reserved                  16 
 12 Inspection  
The purchaser or hi s representative shall have access to the works of the manufacturer at all reasonable times 
and shall be at liberty to inspect and to reject any material which does not conform to the requirements of this 
standard.  
13 Packing  
All reasonable precautions to pr otect the components of the tanks from injury in transit shall be taken. They 
shall be packed in convenient bundle, riveted or bolted together or bound with iron strip or suitable wire. All 
rivets, bolts, nuts, etc., shall be packed in suitable container a ccording to trade practice.  
14 Marking  
14.1 A suitable name plate showing the name of the manufacturer, capacity in litres, dimensions and other 
details as required by the purchaser shall be attached properly so as to be prominently visible. An indelible 
identification mark shall be made by the supplier to facilitate erection, site fabrication and rection of the tank.  
14.2 In addition to the requirements of 1 4.1, the material may also be permanently marked with a 
Standardization Mark  in accordanc e with  relevant National Standards Body  or competent Certification Body’s 
requirements or relevant rules and regulations.  
15 Order information  
When ordering a pressed steel tank, the purchaser shall provide the manufacturer with detailed information in 
accordance with Annex B. The manufacturer may require information in addition to th at required in Annex B. 
 
(normative)  
 
 
 
 
 
 
 DRS 506: 2022  
17                ©RSB 2022  - All rights reserved  
 Annex  A 
(normative)  
 
Infor mation to be supplied with the enquiry and order  
The following details should be supplied by the purchaser at the time of enquiry and order:  
a) type of tank required, that is Type I, Type 2 or Type 3 (Refer to Clause 4)., type of cover (if any), number 
and p osition and type of manhole(s) ; 
b) capacity required in litres or dimensions in metres in multiples of 1.25 m and if any provision is to be 
made for future extension ; 
c) limiting condition, if any, as to space and accessibility for erection, and whether the tank  will be erected 
inside a building or exposed to the weather. If any partition is required, particulars to be given ; 
d) nature and specific gravity of liquid for which the tank is required. If corrosive, particulars to be given. If 
the tank is required for st orage of water, the fact whether it is hard or soft, to be stated. If water level 
indicator is to be supplied, particulars of fixing the water level indicator to be given indicating its location ; 
e) maximum temperature and boiling point of the liquid ; 
f) any spe cial requirements as to jointing material and as to internal and external coating or lagging ; 
g) particulars of connections and drilling required and precise location on tank with dimensioned sketches, 
having regard to possible future requirements ; 
h) whether ex ternal access ladders are required and, if so, particulars to be given ; 
i) details of any existing or proposed supporting structure and height of bottom of tank above ground level ; 
j) whether transverse supporting bearers are required and, if so, particulars as to span and end support 
to be given ; 
k) whether inspection will be made by the representative of the purchaser at the works of the manufacture ; 
l) where erection and test are to be carried out by the manufacturer at site, if so, information as to site 
conditions and accessibility to be given by the purchaser, and whether water or liquid for testing will be 
made available by the purchaser to be stated ; 
m) tolerances of the dimensions, with reference to this standard ; and  
n) reference number of this standard, RS 506. 
  
©RSB 2022  - All rights reserved                  18 
 Bibliography  
[1] ISO 14895:2016 , Small craft — Liquid -fuelled galley stoves and heating appliances  
 DRS 506: 2022  
 
Price based on  17 pages  
©RSB 2022  - All right s reserved