ICS 85.080.01  
 
Reference number
DRS 555: 2023
© RSB2023
  
 RWANDA 
STANDARD  DRS 
555 
 
Firstedition  
2023-mm-dd 
 
Painting of structures in aggressive 
chemical environment— Code of practice  
   
Formatted:  English (United States)DRS 555: 2023 
©RSB 2023- 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 
 
 
 
 
 
 
 
 
© RSB2023 
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 RSB. 
Requests for permission to reproduce this document should be addressed to: 
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KK 15 Rd, 49 
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Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw  Formatted:  French (France)
Field Code Changed
Formatted:  English (United Kingdom)
Formatted:  French (France)DRS 555: 2023 
iii                ©RSB2023- All rights reserved 
 Contents Page 
Foreword ............................................................................................................................................................ iv  
1 Scope ...................................................................................................................................................... 1  
2 Normative references ............................................................................................................................ 1  
3 Terms and definitions ........................................................................................................................... 1  
4 Types of chemical environment ........................................................................................................... 1  
5 Selection of coatings ............................................................................................................................ 2  
6 Types of coatings and their characteristics ....................................................................................... 2  
6.1 General ................................................................................................................................................... 2  
6.2 Oil Base or Oleoresinous ..................................................................................................................... 3  
6.3 Alkyd ....................................................................................................................................................... 3  
6.4 Phenolic .................................................................................................................................................. 3  
6.5 Chlorinated rubber ................................................................................................................................ 3  
6.6 Catalyzed epoxy coatings .................................................................................................................. 34 
6.7 Coal tar epoxy ........................................................................................................................................ 4  
6.8 Bituminous ............................................................................................................................................. 4  
6.9 Vinyl ........................................................................................................................................................ 4  
6.10 Silicone ................................................................................................................................................... 4  
6.11 Polyurethane ........................................................................................................................................ 45 
6.12 Organic Zinc Primers ............................................................................................................................ 5  
6.13 Inorganic Zinc Primers.......................................................................................................................... 5  
7 General instructions .............................................................................................................................. 5  
8 Surface preparation ............................................................................................................................... 6  
9 Safety and handling .............................................................................................................................. 7  
 DRS 555: 2023 
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 Foreword 
Rwanda Standardsarepreparedby 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 Standards 
adopted by Technical committees are ratified by members of RSB Board of Directors for publication and 
gazettment as Rwanda Standards. 
DRS 555was prepared by Technical Committee RSB/TC  056, Paints, Varnishes, Adhesives and Related 
Products.  
In the preparation of this standard, reference was made to the following standard: 
IS 14428: Painting of structures in aggressive chemical environment—Guidelines 
The assistance derived from the above source is hereby acknowledged with thanks. 
Committee membership  
The following organizations were represented on the Technical Committee on Paints, Varnishes, Adhesives 
and Related Products (RSB/TC 056) in the preparation of this standard. 
Star Construction and Consultant (SCC) Ltd 
Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA) 
Ministry of Environment (MoE) 
Rwanda Forensic Laboratory (RFL) 
Rwanda Investigation Bureau (RIB) 
University of Rwanda/College of Sciences and Technology (UR/CST) 
Kigali Water Ltd 
EARTHENABLE Ltd 
AMACO Paints 
Shalom Paints DRS 555: 2023 
v                ©RSB2023- All rights reserved 
 Standards for Sustainability 
REX Paints 
AMEKI Color 
Rwanda Standards Board(RSB) – Secretariat DRS 555: 2023 
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 Introduction 
Several type of coatings and application methods may be recommended for various cases, but each type of 
environment should be considered as a separate case and the choice should depend upon the economics 
involved. The main function of painting in chemical plants is to control corrosion in the capital investments of 
equipment, structures, vessels, piping and buildings. 
Atmospheric corrosion is that environment which is generated by the presence of the elements of nature the 
air pollution of the general industrial area and the traces of chemicals within the plant itself. Chemical spillages 
present unusual problems and are not considered as a part of a corrosive atmosphere. An industrial 
maintenance painting programme is the administration, specification, application, inspection and evaluation of 
protective coating systems. These guidelines, based upon current industrial practices and experiences, 
present an outline of an industrial maintenance painting programme. The outline includes all phases of a 
programme deemed necessary, though emphasis on each phase and manner of accomplishmentof individual 
portions will vary with the following: 
a) size of industrial plants, 
b) type of industrial plant, 
c) corrosive atmosphere, 
d) geographical location, 
e) economy, and 
f) desires of management. 
Because of instances of inadequate hand tool cleaning, owner in certain areas have resorted to specifying 
blast cleaning on all new structures regardless of its feasibility, its environment and type of paint. To avoid 
unnecessary failures or unnecessarily stringent specification in mild environments, it is important to follow the 
good practices outlined in this document. 
 
 DRS 555: 2023 
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 Painting of structures in aggressive chemical environment— Guidelines 
1 Scope 
This Draft Rwanda Standard provides guidelines in the selection of protective coating for painting of metallic, 
concrete and other types of surface of structures subjected to different chemical environment. It also briefly 
describes various types of coatings and the processes of surface preparation for painting. 
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 editioncited applies. For undated references, 
the latest edition of the referenced document (including any amendments) applies. 
RS ISO 4618,  Paints and varnishes — Terms and definitions  
3 Terms and definitions 
For the purposes of this standard, the terms and definitions given in RS ISO 4618 and the following apply. 
3.1 
chemical environment 
exposures in which strong concentrations of highly corrosive gases, fumes, or chemicals (either in solutions or 
as solids or liquids) touch the surface. 
4 Types of chemical environment 
4.1 A normal rural atmosphere is comparatively mild because the only deteriorating influence is the weather. 
Strong sunshine may lead to rapid degradation of some materials. The rural environment may be dry or wet 
and damp. 
4.2 An industrial atmosphere generally is thought of as that found in urban regions near industrial plants or 
industrialized areas. The characteristic of an industrial atmosphere is the high concentration of sulphur 
dioxide. This factor increases corrosion rates and attack on the protective systems. 
4.3 Environments near some types of industrial or chemical plants may be classed as chemical because of 
the presence of strong corrosive agents such as acid fumes, atomized solutions of alkali dust, mist, solvent 
vapours or any of the host of deteriorating substances. 
4.4 The severity of a chemical environment may vary from mild exposures, remote from the source of 
chemical contamination to extremely corrosive situations such as produced by immersion in strong chemicals. 
4.5 The environment described in 4.3 and 4.4 are considered as chemically aggressive which are referred 
hereafter.  
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 5 Selection of coatings 
5.1 The selection of materials involves the evaluation of the generic type of coatings, the brand or 
manufacturer and the application characteristics. Also, the evaluation of expendable materials such as 
sandblasting abrasives are also to be considered. 
5.2 An evaluation programme may vary widely depending upon the size of plant, funds available and the end 
result desired. The evaluation method may consist of one a combination of the following: 
a) Literature description – Manufacturer’s literature and recommendation, organizational publications, 
information from neighbouring plants, etc. 
b) Laboratory test –  Determination of physical characteristics with laboratory apparatus. 
c) Field panels –  Exposure of small panels in the corrosive atmosphere of the plant or area to evaluate the 
performance. 
d) Larger area test –  Application of various materials on steel over an area of more than 2 square metre in 
the corrosive atmosphere. This allows simultaneous evaluation of application characteristics as well as 
performance data. 
e) Limited field tests –  Field application of materials to the steel to be protected over an area over 2 square 
metre. 
f) Actual performance –  Information from records and by observation of actual coatings, applications and 
performance over a long period of time. 
5.3 The most important phase of any evaluation programme is the proper and accurate correlation of derived 
data to actual performance. 
5.4 The types of material used for protection will vary with the service exposure and the life expectancy 
required, or other economic justifications. 
5.5 Final evaluation of the performance of the desired systems as mentioned under 5.2 (d) be arrived by 
working the life of each paint system in sqm/mil. (25 micron/year). 
6 Types of coatings and their characteristics 
6.1 General 
6.1.1 The descriptions of various types of coatings most commonly used in the field are given in order to 
familiarize the field man with their nomenclature and give him an idea about their performance characteristics. 
This at standard cover only those types of coatings which have been used successfully over a period of time. 
It does not cover some of the newer coatings which are still considered to be in the experimental stage as far 
as their in the field is concerned. 
6.1.2 Organic coatings are composed of pigments and vehicles as binders for anticorrosive primers. These 
coatings change from the liquid to a solid film by several mechanisms such as: DRS 555: 2023 
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 a) Evaporation of solvent, 
b) Oxidation, and 
c) Polymerization, either by internal reaction or reaction with an added catalyst or activator. 
6.2 Oil Base or Oleoresinous 
These consist of an oil (Usually linseed, tung, soybean, or castor), which is capable of being converted to a 
solid by reaction with oxygen of the air. Metallic driers are added to accelerate this reaction. The film formed 
has very little resistance to chemicals and has higher permeability to water vapour and other gases than other 
types of films. This permeability makes it a good binder for use in house paints, which if not somewhat 
permeable would blister and peel. An outstanding property of the trying oils is their ability to wet and adhere to 
steel, which accounts for their widespread use in primers. This property is particularly important in instances 
where it is not possible to remove all rust before painting. 
6.3 Alkyd 
These synthetic resins are made by cooking certain acids and alcohols along with varying quantities of drying 
oils. These drying oils impart flexibility to the resin; more the oil in the resin, the more flexible the coating will 
be. However, it also follows that the more the oil length or content, the more coating will resemble the 
oleoresinous type. Alkyds are used in environments mentioned in 4.1 and very mild acidic environments. The 
outstanding properties of alkyds are their gloss retention and stability to sunlight. 
6.4 Phenolic 
Phenolics are formed by reacting phenol with formaldehyde. Air-drying phenolics have better chemical 
resistance and more water resistant than alkyds, but they are less resistant to the effect of ultraviolet light, 
tending to yellow with age and to chalk more rapidly. The phenolic based coatings are suitable for areas which 
are subjected to sunlight and mild chemical environment. 
6.5 Chlorinated rubber 
Chlorinated rubber resins are made by reacting chlorine with natural rubber. Coatings made from chlorinated 
rubber have very good resistance to alkalis, weak acids, and salt water, but should be modified and stabilized 
to make them resistant to sunlight. Their major use is in the coating of offshore platforms, fertilizer plants and 
barges. It is essential that only chemically inert plasticizers are incorporated in the formulation. 
6.6 Catalyzed epoxy coatings 
6.6.1 A small amount of amine or polyamide catalyst or activator is added to the epoxy coating just prior to 
application. This causes a cross-linking of the molecules and curing of the coatings. While these coatings set 
to touch in a few hours, several days are required for them to cure completely and develop their ultimate 
chemical resistance. Catalyzed epoxy coatings have good acid resistance and very good alkali resistance, 
however, their outstanding property is their excellent resistance to solvents. They are widely used for coating 
the interior of products, storage tanks. In sunlight, they tend to develop rapidly (within months) a surface chalk.  
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 6.6.2 The catalyzed coating shall be applied within a few hours after the addition of catalyst, otherwise it 
will set up in the can. Brushes and spray equipment used to apply these coatings shall be cleaned thoroughly 
after use. After the epoxy has cured there is no known way to remove it from the equipment. 
6.6.3 The coating manufacturer should always be consulted before using an epoxy system for an 
equipment which is to immersed in either fresh or salt water. 
6.7 Coal tar epoxy 
These catalysed materials combine the excellent adhesion and water resistance of coal tar with the thermal 
stability of catalysed epoxy coatings. They have high solids content by volume (65 – 85 %) and good stayput, 
allowing thick coatings to be applied in a minimum number of coats. Two coats of 8/10 mils each are 
recommended for most uses. The main uses of coal tar epoxy coatings are for offshore equipment, mud 
tanks, equipment to be exposed to immersion in salt water (particularly boat bottoms), the exterior of pipe 
which is to be underground and the interior of crude tanks. The high degree of impermeability of gases, 
particularly hydrogen sulphide, makes them well adapted to protecting the vapour zones or sour crude tanks. 
6.8 Bituminous 
These coatings are made from coal tar or asphalt. They may be hot-applied cut-back (dissolved in a solvent), 
or emulsions (particles dispersed in a non-solvent). Their widest use lies in protection of buried pipe. The coal 
tar coatings have much better resistance to moisture penetration, to attack by soil organisms, and to 
hydrocarbons than do most of the asphalts. 
6.9 Vinyl 
Vinyl coatings have very good resistance to acids, alkalites, oils and salt water. Their adherence is poor 
unless special vinyl primers are used. For a vinyl system, a bright metal sand is necessary for perfect 
performance. Vinyl coatings have the lowest solid content (and highest chemical resistance) of any of the 
commonly used coatings, therefore multiple coats are necessary to built-up adequate film thickness. 
6.10 Silicone 
Silicone resins, because of their thermal stability are used to make heat-resistant paints. These resins are 
quite expensive;therefore, silicone coatings should be used only if other types of coatings are unsatisfactory. 
Aluminium-pigmented silicone performs well up to 427 ˚C. They are widely used on mufflers, heater stacks, 
and hot surfaces of that type. A white-metal sand blast is necessary for the silicones to perform properly. 
6.11 Polyurethane 
Polyurethane coatings are based on the reaction of a group of chemicals, the disocyanates, with resins or 
chemicals containing alcohol or amine substituents in their structures. The diisocyanates have a high order of 
toxicity and therefore chemically modified to permit their use in protective coatings. 
There are total five types of polyurethane coatings, namely: 
Type 1: Single component urethane – Modified oil-based system. 
Type 2: Single component moisture – Cured urethane system. DRS 555: 2023 
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 Type 3: Single component – Block isocyanate system. 
Type 4: Two component catalyst – Cured polyurethane system. 
Type 5: Two component – Polyol type polyurethane system. 
However, Type 5 is the most practical and widely systems for structural painting. There are two general types 
of two component urethanes; aliphatic and aromatic. The aliphatic type has excellent resistance to weathering 
and most commonly used where colour and gloss retention are important. The aromatic type polyurethane is 
sometimes used as tank linings. When properly formulated, applied and cured, two component polyurethane 
coatings have outstanding hardness, abrasion resistance with chemical properties similar to epoxies. 
6.12 Organic Zinc Primers 
Organic zinc primers usually contain a high loading of zinc dust with organic film formers such as epoxy, 
phenolics or chlorinated rubber. This type of primers has no critical application requirements and are 
commonly applied to blast-cleaned steel at 50 – 70 microns dry film thickness without problems of cracking or 
flaking. 
6.13 Inorganic Zinc Primers 
Inorganic zinc primers are usually referred to as inorganic zinc silicates. All silicate coatings are essentially 
based on a combination of zinc and a complex silicate solution. Such coatings can provide outstanding 
resistance to corrosion in a single coat. These coatings are extremely hard and abrasion resistant and the 
adhesion to metal is of a chemical nature which is one of the strongest bonds that can be obtained between 
two materials. This type of primers has excellent weathering properties and solvent resistance and extensively 
used for preventing corrosion of tank exteriors, structural steel, piping offshore platforms, bridges, marine, etc. 
7 General instructions 
7.1 Protective coatings are measures which can be used in the control of corrosion of producing equipment. If 
used intelligently and properly, they should do so satisfactory job of protecting a metal from a corrosive 
environment. No coatings last forever, and there are no cure-alls. No coatings will work just as well over rust 
as it will over properly prepared surface. 
7.2 The following points should be taken care of: 
a) The surface should be prepared properly; 
b) The correct type of coating for the intended services should be chosen, and applied according the 
manufacturer’s recommendations; 
c) If the job is contracted out: 
1) Adequate and firm specifications, particularly as to film thickness should be mentioned. 
2) Competent inspection of the job should be arranged.  
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 d) Schedule shall be so arranged as to prevent coating damage. When welding above a painted surface, the 
surface should be covered with sand, dirt, sacks or anything that will prevent the weld spatter from 
dropping down and burning holes through the coatings; 
e) The paint should not be overthin. Requisite quantity of thinner shall be added as per the manufacturers 
recommendations to get proper film thickness and flow of paint; 
f) As paints have limited shelf life, procurement instalments should be planned as per requirements; and 
g) If difficulties are encountered with application, or if a coating does not perform as expected, the paint 
manufacturer may be consulted. Manufacturers should send competent technical field representative to 
the job to help out difficulties. 
8 Surface preparation 
8.1 For surface preparation for painting, one should visualize what constitutes the most ideal surface 
condition for a good paint anchor. For general work, this anchor would constitute a metal surface free soil and 
chemical products. It would be a relatively smooth surface free of scale or oxidation products but with a 
mechanical surface anchor of a height known to be suitable for the coating system employed. Mill scale itself 
is a satisfactory surface to paint. If kept intact, it will result in long paint life in mild scale or only moderately 
severe environments. If intact mill scale is painted, long paint life may be expected, in fact almost as long as 
for descaled steel. 
8.2 While it appears desirable to produce the best surface condition before a coating is applied, the cost of 
the finished job should be born in mind. Some service conditions do not require the removal of all of the mill 
scale, rust, and contaminants. As long as the prepared surface is compatible with the coating applied, it will 
serve for a period of time determined by the environment. 
8.3 If the deterioration of paint film is sufficiently slow and the underline metal is not seriously affected by the 
eventual loss of the coating, there is little reason to concentrate on anything but the more economical surface 
preparation methods. 
8.4 Hand tool cleaning is an acceptable method of surface preparation for normal exposure in the 
atmosphere, interiors, for much the maintenance painting, including paints of good wetting ability. Hand 
cleaning will not remove all residue or rust nor will it remove intact, firmly adhered mill scale. For small limited 
areas such as spot cleaning for maintenance priming hand cleaning will suffice, even for paints requiring very 
clean surfaces. 
8.5 Hand tool cleaning shall consist of the following sequence of operations: 
a) Oil grease, soluble welding flux residues and salts shall first be removed by solvent cleaning. Other 
detrimental foreign matter shall be removed by the following operations. 
b) Stratified rust (rust-scale) shall be removed by hand hammering, hand chipping, other hand impact tools, 
or a combination of them. 
c) All loose mill scale, and all loose or non-adherent rust shall be removed by hand wire brushing, hand 
sanding, hand scraping, or by a combination of these methods. DRS 555: 2023 
7                ©RSB2023- All rights reserved 
 8.6 Painting should proceed as soon as possible after the hand cleaning operations. It is not as critical, 
however, as in the case of blast cleaning or pickling where virgin metal is exposed. 
8.7 Blast cleaning is preferable where areas are very large to achieve lowest coats (because of difficulties in 
the reclamation of abrasives). The following factors influence blast cleaning operations: 
a) Type of metal to be cleaned and cleaning rate (speed). 
b) Shape of the part. 
c) Kind of materials to be removed. 
d) The surface finish desired and the thickness of the coating that in anticipated. 
e) Loss of abrasive and breakdown rate. 
f) Hazards to equipment and working conditions associated with abrasive. 
g) Time requirements 
8.8 During the initial set up of the plant all the above can be controlled in addition to protecting adjacent 
properly, particularly machinery, electrical equipment, etc. 
9 Safety and handling 
Aspects of safety and handling during the application of all types of paints mentioned in this specification, 
especially epoxies, polyurethanes, zinc silicates, etc. assume great importance. Diverse chemical ingredients 
used in the formulations as curing agents, hardeners, additives, bases could be aggressive, toxic or 
hazardous in nature. It is therefore mandatory to have full details with complete procedures and precautions 
for safety and handling of coatings from the suppliers and/or manufacturers.  
 
 
 DRS 555: 2023 
 
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