Materials of Construction for Use in Contact With Chlorine

Materials of Construction for Use in Contact with Chlorine

GEST 79/82

11th Edition

July 2013

EURO CHLOR PUBLICATION

This document can be obtained from:

EURO CHLOR - Avenue E. Van Nieuwenhuyse 4, Box 2 - B-1160 BRUSSELS Telephone: 32-(0)2-676 72 65 - Telefax: 32-(0)2-676 72 41

GEST 79/82 11th Edition

July 2013 Page 2 of 21

Euro Chlor

Euro Chlor is the European federation which represents the producers of chlorine and its primary derivatives.

Euro Chlor is working to:

improve awareness and understanding of the contribution that chlorine chemistry has made to the thousands of products, which have improved our health, nutrition, standard of living and quality of life;

maintain open and timely dialogue with regulators, politicians, scientists, the media and other interested stakeholders in the debate on chlorine;

ensure our industry contributes actively to any public, regulatory or scientific debate and provides balanced and objective science-based information to help answer questions about chlorine and its derivatives;

promote the best safety, health and environmental practices in the manufacture, handling and use of chlor-alkali products in order to assist our members in achieving continuous improvements (Responsible Care).

*********** This document has been produced by the members of Euro Chlor and should not be reproduced in

whole or in part without the prior written consent of Euro Chlor.

It is intended to give only guidelines and recommendations. The information is provided in good faith and was based on the best information available at the time of publication. The

information is to be relied upon at the users own risk. Euro Chlor and its members make no guarantee and assume no liability whatsoever for the use and the interpretation of or the

reliance on any of the information provided.

This document was originally prepared in English by our technical experts. For our members convenience, it may have been translated into other EU languages by translators / Euro Chlor members. Although every effort was made to ensure that the translations were accurate, Euro

Chlor shall not be liable for any losses of accuracy or information due to the translation process.

Prior to 1990, Euro Chlors technical activities took place under the name BITC (Bureau International Technique du Chlore). References to BITC documents may be assumed to be to

Euro Chlor documents.



RESPONSIBLE CARE IN ACTION

Chlorine is essential in the chemical industry and consequently there is a need for chlorine to be produced, stored, transported and used. The chlorine industry has co-operated over many years to ensure that its activities cause the minimum harm to the well-being of its employees, local communities and the wider environment. This document is one in a series which the European producers, acting through Euro Chlor, have drawn up to promote continuous improvement in the general standards of health, safety and the environment associated with chlorine manufacture in the spirit of Responsible Care.

The voluntary recommendations, techniques and standards presented in these documents are based on the experiences and best practices adopted by member companies of Euro Chlor at their date of issue. They can be taken into account in full or partly, whenever companies decide it individually, in the operation of existing processes and in the design of new installations. They are in no way intended as a substitute for the relevant national or international regulations which should be fully complied with.

It has been assumed in the preparation of these publications that the users will ensure that the contents are relevant to the application selected and are correctly applied by appropriately qualified and experienced people for whose guidance they have been prepared. The contents are based on the most authoritative information available at the time of writing and on good engineering, medical or technical practice but it is essential to take account of appropriate subsequent developments or legislation. As a result, the text may be modified in the future to incorporate evolution of these and other factors.

This edition of the document has been drawn up by the Equipment Working Group to whom all suggestions concerning possible revision should be addressed through the offices of Euro Chlor.



Summary of the Main Modifications in this version

Section Nature 3. Precision added on the limit values given for the temperature

4.1.1. Introduction of different specifications for carbon steel

TABLE OF CONTENTS

1. INTRODUCTION 6

2. GENERAL COMMENTS 6

3. SUMMARY OF CORROSION RESISTANCE 7

4. MATERIALS 9 4.1. Metallic Materials 9

4.1.1. Carbon Steel 9 4.1.2. Cast Iron 11 4.1.3. Ductile Iron 11 4.1.4. Stainless Steels and Cast Steels 11 4.1.5. Nickel Alloys 12 4.1.6. Titanium 13 4.1.7. Tantalum 13 4.1.8. Copper 13 4.1.9. Silver, Gold 14 4.1.10. Lead 14 4.1.11. Aluminium, Tin, Zinc 14

4.2. Plastics 14

4.2.1. (GRP) Glass Reinforced Plastic 14 4.2.2. (PVC) Polyvinyl Chloride 15 4.2.3. C-PVC - Chlorinated PVC 15 4.2.4. PVDF (Poly Vinylidene Difluoride), PVDF/GRP 16 4.2.5. PTFE - PolyTetraFluoroEthylene 16 4.2.6. ECTFE (ethylene-chlorotrifluoroethylene) 16 4.2.7. FEP (TFE/HFP-copolymer), PFA (Perfluoro-alkoxypolymer), ECTFE (Ethylene chloro-trifluoro-ethylene) 17 4.2.8. Polypropylene, Polyethylene 17 4.2.9. Other Plastics 17

4.3. Other Materials 17

4.3.1. Rubber or Ebonite 17 4.3.2. Graphite 18 4.3.3. Stoneware, Glass, Enamel 18 4.3.4. Brickwork 18 4.3.5. Silicon carbide 18



5. GASKETS 19

6. THIN SECTION APPLICATIONS 19

7. PRECAUTIONARY COMMENTS 19

8. REFERENCES 20



1. INTRODUCTION

This recommendation is written to provide general advice on the suitability of various materials for industrial application with chlorine. It does not attempt to define the various corrosion processes but indicates the conditions under which certain materials can be used or should be avoided. Care must however be taken to consider the possibility of the presence of other constituents in either the chlorine or the materials of construction, as the presence of certain trace components can considerably influence the corrosion behaviour. Practical testing under service conditions is therefore the best guide to the suitability of any particular material. Temperature and velocity may modify corrosion resistance.

The guideline deliberately covers only materials which have been used successfully by at least 2 Euro Chlor companies for more than 2 years. It is recognised that individual companies may have good experience with materials not covered in this guideline, or with a wider range of operating conditions.

The limits quoted should be taken as a guide rather than being treated as accurately defined.

Mechanical properties are dealt with in more detail in specific engineering recommendations such as those issued by Euro Chlor. These recommendations, in any case of uncertainty, should not be taken as a firm guide but reference should be made to a chlorine producer to confirm the suitability of any material for a given duty.

2. GENERAL COMMENTS

Materials of construction must be chosen to suit the conditions under which chlorine is being handled

Wet or dry Gaseous or liquid chlorine Temperature Pressure

For dry chlorine gas (see definition in GEST 10/362 Corrosion Behaviour of Carbon Steel in Wet and Dry Chlorine) steel is the usual material. For liquid chlorine and cold dry chlorine gas, steel with suitable toughness (fine grain carbon steel) should be used, taking into account the possibility of low temperatures from potential depressurisation of the system.

For wet chlorine gas, the usual materials are titanium, rubber lined steel, Glass Reinforced Plastics (GRP), PTFE lined steel, PVC/PVC-C externally reinforced with GRP (PVC/GRP) and PVDF.

When plastic materials are selected, the following items must be taken into account:

resistance to ageing



possibility of damage caused by external factors suitability for high and low temperatures.

Furthermore, attention must be paid of the possible differences in quality of the same generic plastic type, and preliminary tests are recommended to check the suitability for the foreseen operating conditions.

A basic principle in chlorine safety is to learn from previous experience. Caution is therefore necessary before any new material is introduced and extensive testing may be required before any equipment is built.

3. SUMMARY OF CORROSION RESISTANCE

The table below gives general aggregated information on the corrosion resistance of various materials for contact with chlorine. Corrosion resistance is not the only factor in selecting the materials and therefore the table should only be used in conjunction with the comments which follow in the rest of the note.



MATERIAL

CONDITIONS OF SERVICE (1), (2)

WET CHLORINE

GAS

DRY CHLORINE (3), (4) COMMENTS

GAS LIQUID

Non-alloyed carbon steel N G to 120C G 4.1.1 Cast iron N G to 120C G XX 4.1.2

Ductile iron N G to 120C G XX 4.1.3

Stainless steels N G to 150C G 4.1.4

Nickel alloys N (*) G up to 300C G 4.1.5

Titanium (also Pd stabilised)

G to 90C N N 4.1.6

Tantalum G to 150C G to 150C G 4.1.7 Copper N G to 150C G 4.1.8 Brass N A to 150C G 4.1.8 Bronze N G to 150C G 4.1.8 Silver/gold A to 20C A to 20C G 4.1.9 Lead N G to 100C A XX 4.1.10 Aluminium N N N 4.1.11 Tin N N N 4.1.11 Platinum N N N Corrosion resistant polyester resins (reinforced)

G to 90C G to 90C N 4.2.1

PVC A to 60C G to 60C N 4.2.2 C-PVC G to 80C G to 80C N 4.2.3 PVDF G to 120C G to 120C N 4.2.4 PTFE G to 200C G to 200C G 4.2.5 ECTFE G to 100C G to 100C G 4.2.6 FEP, PFA G to 180C G to 180C G 4.2.7 PEEK N N N 4.2.9 Polypropylene N A to 30C N 4.2.8 Polyethylene N A to 30C N 4.2.8 Ebonite G A N 4.3.1 Synthetic rubbers A A N 4.3.1

Silicone rubbers or greases N N N N 4.3.1

Graphite N G to 200 C (with PTFE impregnation)

N 4.3.2

Stoneware and glazed pottery

G XX G XX G XX 4.3.3

Glass G XX G XX G XX 4.3.3

Enamelled steel G G G XX 4.3.3

Brickwork G to 100C G to 100C N 4.3.4 Silicon carbide G G G 4.3.5

* except in some very specific cases

Key behaviour (see comments here below):

G = Good (limited attack) A = Acceptable (attack of the material)

XX indicates the material is not used for construction; only the corrosion resistance is taken into account

N = Must not be used



Comments:

1. Temperatures stated above give an indication of the typical recommended maximum values; they can be influenced by the specific surface area, texture .

2. The above table refers to the non-reinforced plastics without any plasticiser or filler.

3. See definition in GEST 10/362 Corrosion Behaviour of Carbon Steel in Wet and Dry Chlorine

4. For all plastic materials where it applies, the temperature limit could be lower, depending on the supporting material (FRP for example).

4. MATERIALS

4.1. Metallic Materials

Steels cannot be used with wet chlorine, or when moisture can accidentally be present, due to the risk of severe corrosion (pitting in the case of stainless steel),

4.1.1. Carbon Steel

Carbon steel is the most commonly used material for handling liquid chlorine or dry gas.

A grade of steel must be chosen to suit the temperatures which can arise in each case. The use can be restricted by the impact toughness of the steel.

For liquid chlorine and cold dry chlorine gas, fine grain carbon steel with guaranteed low temperature impact properties should be used, taking into account the possibility of depressurising the system (vaporisation of residual liquid chlorine at minus 34C at atmospheric pressure or lower if pressure can go sub-atmospheric).

The following are general requirements for steel used for tanks, pipes, transport equipment ; for valves components, specific requirements are given in the GEST 06/318.

Chemical composition

The chemical composition must comply with the appropriate material specification as required by the relevant design code selected.



Mechanical properties

The actual maximum tensile strength Rm of any component should not exceed the lesser of:

the minimum required by the relevant material specification plus 155 N/mm2,

725 N/mm2 (consistent with RID/ADR).

The stated minimum yield strength Re of the material should not exceed 460 N/mm2 (consistent with RID/ADR).

The minimum elongation at fracture (in % on standard 5.65So gauge length) should be at least 10,000 / Rm (consistent with RID/ADR), or 20% whichever is the higher.

Low temperature carbon steel materials shall be Charpy V-notch (CvN) impact tested in accordance with EN ISO 148. Rolled materials should be tested transverse to the rolling direction. The impact test temperature should be a maximum of minus 40C, or a lower temperature if required by the design conditions and design code. The average and minimum CvN energies recorded for three tests samples should be as defined by the table here below (cf. EN 13445-2 part 2, annex B1).

This table quotes the required values for 10*10mm sample; for reduced size samples, the equivalent values may be used, according to the test methods.

Minimum yield strength according to specification

N/mm2

Average impact energy for 3 tests

J

Minimum impact energy for any one

test

J

355 27 19

460 40 28

Note: where permitted by the design code, it is acceptable to convert (cf. PD5500) recognised standard impact requirements carried out at a lower temperature to an equivalent at minus 40C using a factor of 1.5 J/C as long as it is in the range 18-47J (e.g. ASTM A350 LF2 Class 1 requirement of 20J @ minus 46C can be considered equivalent to 29J @ minus 40C and therefore in compliance with this recommendation).

All steel components must be thoroughly degreased, cleaned and dried to remove surplus oxide, oil, hydrocarbons, moisture, etc, before coming into contact with chlorine, see GEST 80/84 - Code of Good Practice for the Commissioning of Installations for Dry Chlorine Gas and Liquid.

1 EN 13445-2 Unfired Pressure Vessels - Part 2: Materials - Annex B: Requirements for prevention of brittle fracture at low temperatures



In contact with dry chlorine, carbon steels become covered by a layer of ferric chloride. It is this layer that protects the underlying carbon steel from further attack2; it can nevertheless be destroyed by different mechanism, resulting in the corrosion of the underlying steel (see GEST 10/362 Corrosion Behaviour of Carbon Steel in Wet and Dry Chlorine).

In certain circumstances where there is a risk of traces of hydrocarbon based oils, water or rust being present, reaction with chlorine can increase the temperature sufficiently to lead to spontaneous ignition of steel.

The use of steel with a high specific surface area, such as steel wool, should be avoided. When chlorine reacts with iron, the temperature can increase sufficiently to cause ignition of steel.

Forged or cast steel can be used on condition that the mechanical property of the fabricated components have been studied for the range of temperatures and stress which might be encountered.

4.1.2. Cast Iron

In the past cast iron was frequently used for dry chlorine, but it is not the case anymore and its use on pressurised chlorine duties should be abandoned for safety reasons due to its low fracture toughness.

The corrosion behaviour in the presence of chlorine is similar to that of normal steels, and the temperature should be below 120C.

Its use in chlorine, however, is not advisable except under specific well defined circumstances for the manufacture of components where there will be no problem due to mechanical shock (poor impact toughness) or tensile forces. With cast iron components, the material needs to be checked for absence of defects which could cause porosity to chlorine under pressure.

4.1.3. Ductile Iron

Rarely used, its corrosion behaviour in the presence of chlorine is similar to that of carbon steel. Its use in chlorine is however not advisable, except under specifically well-defined circumstances for the manufacture of components where there will be no problem due to mechanical shock (poor impact toughness) or tensile forces, e.g. for PTFE-lined valves for wet chlorine. The operation temperature is also limited to 120C.

4.1.4. Stainless Steels and Cast Steels

Stainless and cast steels are suitable for use with dry chlorine.

They should not generally be used if there is the likelihood of contamination with water. Chlorine contaminated with moisture forms HCl which results in pitting corrosion on stainless steel. For this reasons, stainless steels are not recommended for thin section applications e.g. bellows and bursting disc.

2 Hammink, M.W.J. and Westen, P.C. - Modern Chlor-Alkali Technology [3] 71-81 (1985)



They are sometimes used in preference to normal steel:

with dry hot chlorine gas, because of their improved resistance at higher temperatures (up to 150C). This resistance to chlorine at higher temperature increases with the nickel content. For stainless steels containing less than 10% nickel (ferritic, martensitic, duplex) there can be some restriction due to the impact toughness; these steels can be used on certain duties with chlorine gas up to a maximum of 250C.

for components where improved low temperature fracture toughness is required.

When used at elevated temperatures (>50C) the risk of chloride stress corrosion cracking (SCC) shall be considered. SCC can lead to serious failure of equipment even in the absence of obvious corrosion damage. Chlorides from the external environment that become trapped in damp lagging on stainless equipment can cause particular SCC problems. The risk can be reduced by protecting the stainless steel with a suitable paint system, and by wrapping the equipment in aluminium foil under the insulation.

Duplex stainless steel and high alloyed stainless steels (super stainless steels) have greater resistance to pitting corrosion, Stress Corrosion Cracking and also higher temperature limits in gaseous chlorine.

4.1.5. Nickel Alloys

4.1.5.1. Alloy 200, 400, 600 and 625

These materials cannot be used on wet chlorine.

For dry chlorine gas, Alloy 200, 400, 600 and 625 are suitable up to 300C.

Pure nickel (alloy 200) is only used in thin wall applications e.g. bursting discs, and as a lining material because of its poor mechanical properties.

4.1.5.2. Alloy C4, C22 and C276

Alloy C-4 and Alloy C276 are often used for components for dry chlorine. The low temperature mechanical properties are excellent (to



4.1.6. Titanium

Different grades of titanium are frequently used in pipework, machines, valves and heat exchangers on wet chlorine gas, chlorinated water applications or sodium hypochlorite duties.

Titanium cannot be used on dry chlorine duties, due to the risk of fire, and precautions must therefore be taken on all applications as detailed in TSEM 93/192 - How to use Steel and Titanium Safely. A basic summary of the points is as follows:

The water content in the gaseous phase has to be always kept at least equal to the water partial pressure at 15C3,

The maximum allowable temperature is 90C,

Care shall be taken of local situations (e.g. depressurisation after a valve) with potential risk of erosion of the protective titanium dioxide layer and/or temporary desaturation of the gases water content....

There are many different types of titanium used on plant, both pure (e.g. grade 2) and alloys e.g. alloys with palladium for increased resistance to crevice corrosion (e.g. grade 7,11). The grade used should be selected based on the specific application.

4.1.7. Tantalum

Tantalum is the only metal that can be used without restriction on wet and dry chlorine but its limited mechanical strength and the possible risk of creep have to be taken into account. Due to its high price, however, it is used only for special equipment parts such as transmitter membranes and bursting discs.

Tantalum can also be affected by hydrogen embrittlement, for example as a consequence of the corrosion of adjacent materials.

4.1.8. Copper

Copper is resistant to dry chlorine gas or liquid (but not to wet chlorine). The use of copper is restricted to flexible connections for drum and cylinder filling, but it becomes embrittled by frequent stressing and requires regular stress relieving by moderate heat treatment. The operating temperature is limited to 40C maximum.

Certain alloys of copper (such as brass or bronze) have been proved acceptable by long service experience (e.g. certain cylinder valves) but require regular inspection and frequent replacement (risk of cracks). Ammonia in the atmosphere (e.g. from leak-testing chlorine joints) can cause stress corrosion cracking in copper and its alloys.

3 Taking a safety margin with respect to the 13C minimum referred to in the TSEM 93/192



4.1.9. Silver, Gold

These metals are resistant to dry chlorine (not to wet chlorine) but they have poor mechanical properties. They are sometimes used for protective membranes and bursting discs.

4.1.10. Lead

Lead is resistant to dry chlorine and the rate of attack upon lead by moist chlorine is low.

Lead can be used as a trapped gasket in some circumstances, but otherwise its use with chlorine is not recommended on safety reasons because of its poor mechanical properties.

Lead-antimony alloys are sometimes used for protective membranes, because they are resistant in the presence of moisture.

4.1.11. Aluminium, Tin, Zinc

None of the above metals should be used for chlorine, nor should, in general, alloys based on these materials. They are not resistant to chlorine (poor mechanical properties, risk of severe corrosion with wet chlorine and/or risk of fire).

4.2. Plastics

The following comments deal only with the use of the materials on construction duties or as a lining. Their behaviour when used on specialised duties is dealt with in sections 5 and 6. Most of these plastics cannot be used with liquid chlorine.

They are slowly attacked by chlorine and require a schedule of inspection and replacement before they become defective. Many of them are liable to stress corrosion cracking and the fabrication of components or systems from plastics should avoid regions of high stress during manufacture or service.

4.2.1. (GRP) Glass Reinforced Plastic

Certain chemically resistant resins, such as vinyl esters and modified polyesters, exhibit excellent performances in wet and dry chlorine gas environment at temperatures up to 80C, The GRP laminates can suffer from chlorination in service, which lead to thinning, and an additional corrosion allowance should be considered in the design to provide an economic operational life.

With precautions, the material can be used down to minus 20C, but there is a risk of embrittlement below 0C.

Long term performance of GRP equipment is highly dependant on the method of construction. For example all chopped strand mat (CSM) constructed equipment tends to have longer operational lives than CSM/woven roving construction



equipment (woven roving constructions are usually thinner with a higher glass content resulting in greater loss of strength per unit thickness of chlorination).

There are a number of commercially available materials that have been confirmed as suitable for use on chlorine. As not all resins are equivalent, advice on the type used, its method of fabrication and use should be checked with an experienced chlorine manufacturer before selection and installation. The operational life depends on laminate construction and resin type.

GRP must not be used where liquid chlorine may be present.

4.2.2. (PVC) Polyvinyl Chloride

PVC has a fair resistance to gaseous chlorine, and is especially good for wet gas. After prolonged use the wall thickness will reduce due to surface chlorination/corrosion (periodic check is recommended). The material may become brittle below 0C and therefore can be susceptible to cracking and failure due to impact.

Exposure to chlorine containing liquor that experiences wide variations in pH can lead to rapid thinning as the chlorinated layer is removed.

PVC has low fracture toughness and pressure containing equipment should be reinforced externally with GRP to improve mechanical strength.

PVC is subject to stress corrosion and it is recommended that the material should be stress-relieved before use.

PVC is susceptible to environmental cracking with welds being particularly vulnerable.

Operating pressures must be limited and support must be provided. The acceptable temperature range is between minus 5C and 40C, but PVC is generally externally reinforced with GRP to improve the mechanical strength, and can then be used to 60C.

As the thermal expansion of PVC is different from that of GRP, the reinforcement is often adhered to the PVC (but take care of cracking risk). This is achieved by using a priming coat in the PVC/GRP interface so that PVC and GRP are chemically bond to each other. This procedure unfortunately gives a brittle behaviour in the PVC which can be dangerous4.

PVC and PVC/GRP must not be used where liquid chlorine may be present.

4.2.3. C-PVC - Chlorinated PVC

Chlorinated PVC (C-PVC) has greater mechanical strength, temperature and chemical resistance than PVC in certain (wet) chlorine gas environments. It also

4 Bergman G. and Petersson K. - Brittle Behaviour of PVC-lined FRP structures. Swedish

Corrosion Institute, Project report 66 226:2



has the advantage of being resistant to higher temperatures (operation acceptable till 90 C with reinforcement).

Special attention is needed to join sections by either hot gas or butt fusion welding (check the experience of the welding company) and solvent cementing (use of appropriate silica-free solvents).

Both PVC-U and C-PVC have relatively low fracture toughness and pressurised equipment should be externally reinforced with GRP.

C-PVC and C-PVC/GRP must not be used where liquid chlorine may be present.

4.2.4. PVDF (Poly Vinylidene Difluoride), PVDF/GRP

PVDF has good resistance from minus 40C up to 120C on wet or dry chlorine gas. At the upper end of this temperature range it stands up better than PVC and polyesters, but is subject to chlorination.

Like most plastics already listed, the material is liable to stress corrosion cracking. The stress cracking problem for PVDF is caused by caustic soda and also atomic chlorine radicals (for example due to UV light or in certain chemical reaction conditions).

PVDF grades specified as "Atomic chlorine resistant" should be used on chlorine duties. PVDF can also be reinforced externally with GRP to give improved mechanical strength for applications at higher pressures.

PVDF can be used as lining of steel pipes and equipment, but care must be taken due to the permeation of chlorine which may attack the support material.

PVDF and PVDF/GRP must not be used with liquid chlorine.

4.2.5. PTFE - PolyTetraFluoroEthylene

PTFE resists wet, dry and liquid chlorine from minus 50C till 200C.

Due to its poor mechanical properties, PTFE should always have a supporting material. However, it should be noted that chlorine can diffuse through PTFE, which is not completely impervious (particularly at elevated temperatures). The problem of permeability can be reduced by using greater material thicknesses. Where PTFE is used as a protective layer, the integrity of the supporting material must be regularly inspected.

4.2.6. ECTFE (ethylene-chlorotrifluoroethylene)

ECTFE resists wet, dry and liquid chlorine.

This material has one of the lowest chlorine permeation rates of all fluoropolymers, but application under pressure above 100C is not recommended (loss of tensile properties above 120C).



As the permeation of water is one of the lowest, this product is good for wet chlorine applications.

ECTFE is susceptible to stress cracking in sodium hypochlorite.

4.2.7. FEP (TFE/HFP-copolymer), PFA (Perfluoro-alkoxypolymer), ECTFE (Ethylene chloro-trifluoro-ethylene)

Various fluorinated copolymers are also used because of their corrosion resistance to wet or dry chlorine. They can be more easily fabricated than PTFE with fewer problems of permeability. The maximum allowable temperature is usually 180C, and the minimum minus 50C.

PFA is more permeable to water than PTFE (and especially at higher temperature) which needs to be considered for wet chlorine service.

4.2.8. Polypropylene, Polyethylene

Polypropylene and polyethylene have some resistance to dry chlorine gas at low temperature but must not be used with wet chlorine gas. Both are more severely attacked by chlorine above 30C (maximum allowed). The minimum temperature for polyethylene is minus 5C, but polypropylene can be used till minus 40C.

These materials are subject to embrittlement; they are less resistant than PVC and are mostly used in low chlorine concentration environments.

It is recommended that polypropylene be stress-relieved before use.

They must not be used with liquid chlorine.

4.2.9. Other Plastics

Several other specialised plastics have been developed and tested on chlorine duty (e.g. Acrylonitrile/Butadiene/Styrene copolymers). Their use with chlorine gas can only be recommended where practical experience has been demonstrated as suitable for a particular duty (check with experienced chlorine manufacturers).

Remark: PEEK (polyether-ether-ketone) is commonly used in valve shaft bearing. This material has inadequate resistance to chlorine and can swell, leading to seizing of valves).

4.3. Other Materials

4.3.1. Rubber or Ebonite

All forms of synthetic or natural rubber lack mechanical strength and chemical resistance to chlorine is strongly dependant on rubber formulation. Any rubber should be thoroughly evaluated before use. The slow rate of attack on some



rubber grades in chlorine gas means that it is frequently used as a lining material for chlorine duty up to 85C (depending on the grade of rubber).

It must not be used on liquid chlorine duty.

4.3.2. Graphite

Graphite is produced with phenolic resin impregnation and also PTFE impregnation. Graphite is rarely used on dry chlorine applications with metallic options being the norm. Manufacturers data does, however, support the PTFE impregnated form up to 200C whereas the phenolic resin impregnated form is limited up to 50C.

On wet chlorine duties both PTFE and phenolic resin impregnated graphite are very limited in both temperature and gas concentration and hence should only be used with extreme caution, in any case not with liquid chlorine.

Their use with chlorine gas can only be recommended where practical experience has been demonstrated as suitable for a particular duty (check with experienced chlorine manufacturers).

4.3.3. Stoneware, Glass, Enamel

Ceramics and glass show good resistance to wet as well as to dry chlorine, but their breaking strength is so low that their use in technical applications has constantly declined. They are still used today in laboratories and to a small extent for lining steel vessels, also for enamelled steel containers.

These materials must not be used on liquid chlorine duty since they are very sensitive to thermal shocks.

4.3.4. Brickwork

Anti-acid bricks are used for lining of wet chlorine towers. Cement should be chosen with good chemical resistance to all the chemicals which are present. An impervious lining should be used between the brickwork and the steel vessel.

These bricks have a poor shock resistance.

Brickwork will not be used on dry gaseous or on liquid chlorine.

4.3.5. Silicon carbide

Silicon carbide is chemically resistant to dry and wet chlorine, and is normally used for the liquid chlorine canned motor pump bearings, but has a poor resistance to mechanical and thermal shocks.



5. GASKETS

For gas containing systems (wet or dry), a certain amount of corrosive attack on rubber based on a synthetic elastomer is acceptable so long as the jointing system retains the necessary seal under service conditions. However, for liquid chlorine systems, whatever the pressure, reactive gasket materials such as rubber must not be used.

See GEST 94/216 - Experience of Non-Asbestos Gaskets on Liquid and Dry Chlorine Gas Service.

6. THIN SECTION APPLICATIONS

Certain duties such as flexible bellows, bursting discs, etc., demand the use of thin cross section components. In these circumstances the material must be effectively non-reactive to chlorine and not rely on a protective ferric chloride surface layer.

The most commonly used materials are:

for dry chlorine : nickel, tantalum, Alloy 400 and Alloy C4, C22 and C276 (stainless steel 316S/S is used, but with risk of stress corrosion cracking)

for chlorine with traces of moisture : tantalum

for wet chlorine : tantalum

7. PRECAUTIONARY COMMENTS

The above comments under sections (mainly 4.2) concern the pure materials, without plasticisers, fillers, coatings, greases or other potentially reactive ingredients. Therefore the choice of materials of construction for many systems must be controlled to avoid the introduction of materials which could react with chlorine.

It is also important when using any component (which is itself made from a satisfactory material for use with chlorine) that separates chlorine from another fluid that account is taken of the potential for leakage. This could occur in components associated with heat transfer or hydraulic systems, where it is important to make sure that the fluid is not reactive with chlorine and to avoid products such as water, silicone fluids, hydrocarbon oils, etc. Suitable materials for lubrication or hydraulic or heat transfer fluids are fully chlorofluorinated fluids which are non-reactive to chlorine gas or liquid, e.g. fluids based on PFPE (Perfluoro-polyether) or PCTFE (Polychloro-trifluoro-ethylene).

All ancillary equipment (instruments, sealing arrangements, etc.) should always be made from materials which are compatible with chlorine. Materials used for thermal insulation should also be selected from those, which do not react readily with chlorine or generate corrosive products under service conditions.



8. REFERENCES

GEST 80/84 - Code of Good Practice for the Commissioning of Installations for Dry Chlorine Gas and Liquid

TSEM 93/192 - How to Use Steel and Titanium Safely

GEST 94/216 - Experience of Gaskets on Liquid and Dry Chlorine Gas Service

GEST 06/318 Valves Requirements and Design for Use on Liquid Chlorine

GEST 10/362 Corrosion Behaviour of Carbon Steel in Wet and Dry Chlorine



Industrial consumers of chlorine, engineering and equipment supply companies worldwide and chlorine producers outside Europe may establish a permanent relationship with Euro Chlor by becoming Associate Members or Technical Correspondents.

Details of membership categories and fees are available from:

Euro Chlor Avenue E Van Nieuwenhuyse 4 Box 2 B-1160 Brussels Belgium

Tel: +32 2 676 7211 Fax: +32 2 676 7241 e-mail: [email protected] Internet: http://www.eurochlor.org

Documents

Materials of Construction for Use in Contact With Chlorine