Quick viewing(Text Mode)

HGR-B9118-Is02-Boiler Water Treatment

HGR-B9118-Is02-Boiler Water Treatment

Ref No: HGR-B9118 Issue No: 02 Issue Date: June 2012

HERITAGE RAILWAY ASSOCIATION

GUIDANCE NOTE

BOILER TREATMENT

Purpose This document describes good practice in relation to its subject to be followed by Heritage Railways, Tramways and similar bodies to whom this document applies.

Endorsement This document has been developed with and is fully endorsed by Her Majesty’s Railway Inspectorate (HMRI), a directorate of the Office of Rail Regulation (ORR).

Disclaimer The Heritage Railway Association has used its best endeavours to ensure that the content of this document is accurate, complete and suitable for its stated purpose. However it makes no warranties, express or implied, that compliance with the contents of this document shall be sufficient to ensure safe systems of work or operation. Accordingly the Heritage Railway Association will not be liable for its content or any subsequent use to which this document may be put.

Supply This document is published by the Heritage Railway Association (HRA). Copies are available electronically via our website www.heritagerailways.com

Issue 02 page 1 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler

Users of this Guidance Note should check the HRA website to ensure that they have the latest version.

Table of Contents 1. Introduction...... 3 2. Units...... 3 3. Personal Protective Equipment ...... 3 4. Basics of Water Treatment ...... 3 5. Water Treatment Options ...... 5 6. The Consequences of Water Treatment ...... 5 7. Testing and Chemical Dosage ...... 6 8. Points to Consider ...... 6 9. New ...... 7 10. Conclusion...... 7 11. References ...... 8

Issue 02 page 2 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment

1. Introduction This Guidance Note is one of a series dealing with locomotive boilers that were produced by the 2006-8 meetings on “ Codes of Practice”. Railway locomotive boilers are designed to create, store and distribute steam at high pressure. The working life of such a boiler can be considerably shortened if due care is not taken at all stages of inspection, repair, running maintenance and day-to-day running. In the past there have been a series of accidents and explosions owing to work being undertaken without having due regard to the inherent risks involved. It is with that in mind that HMRI and HRA set up the series of meetings of boiler practitioners to discuss the issues; distil good practice and codify it into this series of Guidance Notes. This guidance is written for the assistance of persons competent to perform these tasks. In places the terminology used may be specific to such practitioners. This guidance should also be useful to those in a supervisory or more general role. However no work should be undertaken unless the persons concerned are deemed competent to do so. Where managements decide to take actions that are not in agreement with these recommendations, following appropriate risk assessments or for other reasons, it is recommended that those decisions are reviewed by the senior management body of the organisation concerned and a formal minute is recorded of both the reasons for and the decision reached.

2. Units The dimensions in this document are variously described in a mixture of imperial and metric units. Where practical equivalent dimensions have been shown but in some cases the dimensions do not easily equate and so the units in force at the time the original designs were documented have been used. The term “p.s.i.” is used to indicate pressures in pounds per square inch.

3. Personal Protective Equipment Before undertaking any works a risk assessment must be conducted. Protective equipment is to be supplied and used at work wherever there are risks to health and safety that cannot be adequately controlled in other ways. The equipment must be • In accordance with the latest Personal Protective Equipment regulations. • Properly assessed before use to ensure it is suitable. • Maintained and stored properly • Provided with instructions on how to use it safely • Used correctly by those undertaking the work. 4. Basics of Water Treatment The function of the steam locomotive is to evaporate water in a boiler to supply steam to transfer heat energy for conversion into tractive effort to propel itself and for the haulage of trains. Early steam locomotives were operated at comparatively low steam pressures and used wrought iron plates in the construction of their boilers. As trains became heavier and improvements in efficiency were dictated, higher boiler pressures proved necessary. The thickness of iron to meet such demands became impracticable and mild steel for boiler construction was universally adopted in order to reduce weight by using the stronger material. A consequence was that became more prominent, except where the was naturally “soft” and non-acidic. Throughout the steam era, various attempts to mitigate the effect of corrosion were made, including mechanical descaling, frequent boiler wash outs, use of plants and chemical dosing. The chemistry of the corrosion process has been understood since the turn of the 19th Century with land and marine boilers comparatively easy to control, especially where a closed circuit thermal cycle was involved. Since the Stephensonian locomotive exhausts to atmosphere, the water feed is constantly being replenished

Issue 02 page 3 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment and in course of the route, variations of water quality are found which, if untreated, can have differing effects on boilers. The most notable effects are:- • Corrosion of the internal boiler surfaces leading to leakage and eventual failure. • Formation of scale with a loss of thermal conductivity leading to overheating and eventual failure. • Water carry over or priming leading to overheating and failure of the , disruption of lubrication and abnormal wear of valves, pistons, liners and bores. Water is a compound of hydrogen and which has the appearance of being a clear liquid, but depending on its source, can contain impurities that vary considerably from one area of the country to another. Water is often described as soft or hard depending on the concentration of and salts dissolved in the water. Where water emanates from predominantly granite sources, such as in Dartmoor, Scotland, Wales and the Lake District, very soft are found. In Southern areas where the geology is predominately limestone and chalk the water is very hard. In the Midlands a combination of hard and soft waters may be found but some of these waters may also be salty. Another important consideration with feed waters is the acidity and oxygen content and with mains water, its chlorine content. The total weight of all solids in solution in a given volume of feed water is referred to as Total Dissolved Solids (TDS). The concentration of TDS is measured in parts per million (ppm). In addition to calcium and magnesium salts, there are often traces of other salts and metals. Non soluble contents in the are manifest in the form of suspended matter or sludge. Scale forms when the concentration of calcium and magnesium in the water exceeds the solubility of calcium and magnesium carbonate in boiler water. If silica is also present, magnesium silicate forms which acts like a cement to form a smooth glaze with the or sulphate. Also dissolved in the boiler water is oxygen, and in some cases, sulphur dioxide in varying proportions. A layer of scale reduces the thermal conductivity of the boilerplates and tubes and causes overheating, distortion, weakening and corrosion of the fired surfaces. Corrosion is a term used to describe the degradation of a metal to its oxide or salt. The main factors involved in this aqueous process are the concentrations of oxygen, hydrogen (acidity) and dissolved salts and the presence of dissimilar metals, and time. The basic aim of boiler feed water treatment is to reduce oxygen and hydrogen ions to the absolute minimum to eliminate corrosion and enable insoluble deposits to be non-adherent. Since the start of the twentieth century railway engineers have experimented with the addition of carbonate (soda ash) and thereby providing in the boiler water (to facilitate low Hydrogen levels) and oxygen absorption. Such treatment followed those used in land and marine practice. This had the effect of preventing scaling and corrosion and was developed into the “TIA” (Treatment Integral Armand) boiler water treatment system which had a dramatic effect in reducing the amount of boiler maintenance and its associated costs. Water treatment was employed in Britain in BR days using the ICI/Alfloc system and in North America using similar products with good results being obtained. There was one drawback, however, whereby higher concentrations of TDS and sludge, which were consequent of the chemical additions, tended to cause foaming and water carry-over. The TDS had therefore to be carefully controlled and the practice of “blowing down” was found necessary to ensure that TDS levels did not lead to heavy carry-over. Anti- foaming compounds were also used at high TDS levels to reduce water carry-over. Boiler water alkalinity is measured in pH (Power of Hydrogen). Zero pH is associated with high (high hydrogen ion) concentration, pH 7 is referred to as neutral and pH 14 with high alkali (very low hydrogen ion) concentration. The selection of a boiler water treatment system requires careful consideration, since with all actions there are consequent reactions. Careful judgement of the chemical tools available needs to be made bearing in mind the consequences of their use. The following discourse is aimed at describing the considerations in selecting the appropriate water treatment and the controls to be adopted to ensure safe operation of boilers. It is important to note, however, that water treatment is not a cure for normal wear and tear, mismanagement of the boiler or for failings which are consequent of poor workmanship or shortcomings of the boiler design.

Issue 02 page 4 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment

5. Water Treatment Options There are two methods for the treatment of feed waters used for steam locomotive boilers based on BS 2486(1997) "The treatment of water for steam boilers and water heaters". External feed water treatment. This is in the form of a fixed water treatment plant which provides reduced impurity, chemically dosed water ready for use. In the past Soda/Lime plants or base-exchange softeners have been used. Modern technology has provided which produces water with very few impurities. Internal boiler water treatment. This is where chemicals, usually soda ash () or caustic soda (sodium ) and tannin, are added directly to the boiler or boiler feed water either as powders or solutions. If the TDS reaches a level where carry-over occurs, suitable antifoams can be employed or the boiler water can be blown down or changed. It is safe to use where fireboxes are employed and will deal with most feed waters supplied in the British Isles. Regular boiler water sampling is recommended and subsequent variation of the chemical dosage may be necessary to ensure that the boiler water conforms to the specification stated in British Standard 2486(1997). Alkalinity (pH) 10.5 to 12.0 Tannin (ppm) 120 to 160 Total Dissolved Solids (TDS) (ppm) 3500max Departures from the above recommendations can be made, with the tannin down to 60ppm and TDS above 3500ppm with anti-foam, without harming the boiler. The actual water treatment system selected depends on a number of factors. Where the treatment process is not fully understood, locomotive maintainers should seek professional advice from a recognised boiler water treatment specialist who has proven experience with the treatment of locomotive type boilers prior to the introduction of any form of chemical addition.

6. The Consequences of Water Treatment Any operator of mechanical plant seeks to minimise cost and maximise utility, no less so than those involved with the management and operation of steam locomotives. These two ideals inevitably pose a compromise. With the use of appropriate boiler feed treatment, savings can be expected due to the following:- • Minimal corrosion of all internal boiler and steam supply line surfaces • Elimination of scale deposits and the risk of tube and plate failures • Improved evaporation and reduction of fuel consumption • Purer steam production with longer lasting superheater elements • Less wear and tear on the wearing surfaces of cylinders, valves and pistons • Less boiler leakage • Performance of maintained over longer periods • Longer periods between boiler wash outs • Longer periods between boiler maintenance and tube renewals • Water tank and tender internal surfaces protected against corrosion • Virtual elimination of corrosion during periods of lay up • Improved locomotive availability

Material Safety Data Sheets must be kept on hand at all times. All persons using chemicals should: o Be familiar with the content of the Material Safety Data Sheets o Know where to find them o Be aware of how to handle the chemicals in a safe manner o Know the appropriate treatment procedures if coming into contact with the chemicals or treated water.

Issue 02 page 5 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment

o Lead is very slowly attacked by medium alkali in the boiler water and thus fusible plugs can be copper plated to resist corrosion. o Regular chemical analysis needs to be carried out to assess the pH, TDS and Tannin levels of the boiler water. o Dosing of the chemical additives in response to the chemical analysis needs to be carefully controlled. o A “blowdown” regime is necessary to reduce excessive TDS levels if antifoams are not used. o Wash out periods need to be optimised to remove sludge and old dislodged scale. • Boiler water with a pH above 12 must not enter the drainage system untreated and the alkalinity must be lowered before being allowed to enter the mains drainage system. Where this cannot be arranged, removal by a specialist waste disposal company may be considered. 7. Testing and Chemical Dosage It is necessary to measure the TDS, alkalinity (pH) and tannin concentration of the boiler water. There are several methods of doing this. Possibly the easiest is to use electronic meters or specialised test kits. An accurate thermometer may also be required depending on the method in use. To measure pH, a proprietary electronic direct read out instrument can be used. To measure TDS a simple specific gravity meter or electronic instrument can be employed. Such items are readily available from specialist suppliers. It is important to periodically calibrate such equipment to ensure accuracy. Test Kits are available to measure the concentration of Tannin in ppm. The amount of chemical to be added may require to be varied depending on the initial condition of the boiler. Specialist advice should be sought on this process. To calculate the dosage, the water capacity of the boiler must first be established. Following boiler wash out, the initial charge of chemicals is placed directly into the boiler and the amount will depend on the quality of the feed water being used. Subsequent additions of chemicals may be made to the water tanks or tender following routine testing of the boiler water. Variations in feed water quality resulting from a change in the water source or storage systems should be referred to the boiler feed treatment specialist for further analysis. Water sample collection can be made from the water gauge drain or via a specially fitted small bore sampling cock installed, with the acceptance of the appropriate regulatory body, below the normal water level and with a small condenser coil. Sampling should be taken initially at least once during the day’s operation, however, the sampling period may be extended following experience with use of the treatment system. Results may be recorded in a log book and transferred to a permanent record sheet. The sampling procedure and record sheet should be described in the locomotive Maintenance Plan.

8. Points to Consider The following supplementary points are provided for information and consideration when selecting a water treatment system:- • Water side corrosion of copper is very limited, except under extreme conditions: o Strongly acidic o Strongly alkaline in the presence of oxygen and o Non-aqueous fused in the presence of oxygen • Corrosion of waterside copper is unlikely to occur unless use is made of contaminated water (from a canal or river, i.e. containing fertiliser or animal wastes). Corrosion will occur when high concentrations of Sodium Hydroxide (caustic soda) are present in the boiler water if it leaks into rivet holes or seams. The use of suitable helps to prevent this. • Hydrogen embrittlement of copper and cracking only occurs in extreme non-alkaline conditions when it is overheated, highly stressed and in the presence of small inclusions of copper oxide, typically at any oxy-acetylene welds. • A phenomenon known as “caustic embrittlement” was believed to occur when steel is subject to very high alkalinity under the influence of high and stresses in excess of the yield point. This type of cracking is now thought to be caused by thermo-mechanical fatigue which is increased by excessive cold working and / or corrosive boiler water. It sometimes results in star type cracks

Issue 02 page 6 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment

around tube ligaments or stay holes. Failure from this mechanism can be mitigated by the use of suitable tannin compounds. • Washouts – The principle aim of a wash out is to remove accumulated mud and scale. When using water treatment the sludge formed by the chemical reactions is kept mobile and non-adherent and thus hard scale is not formed. The wash out period can then be safely extended, however, this will depend upon the initial condition of the boiler and such extended periods between wash outs may take several seasons of experience to establish. • Adding treatment to a previously non treated boiler will gradually break up and dissolve the existing scale deposits. It is important to note that scale has no mechanical strength and that the treatment may well reveal wastage that was undetected in the past. Actions will be required to replace any thinned, pitted areas or badly fitting components such as screwed stays and rivets. It will also be likely that light re-rolling and beading of tube ends, caulking of stays, rivets and seams may be required. Water treatment will not cause further leakage, in fact, leakage problems should be virtually eliminated once the remedial work has been completed and treatment has become established. • Corrosion protection during lengthy periods out of service has traditionally involved emptying the boiler and allowing air to circulate through the mud door and washout plug holes. Scale or sludge left behind may retain water or harden. Degradation is inevitable, especially in the presence of water from rain, condensation or high humidity. o When a boiler which has been water treated is going to be stored it should be thoroughly washed out, including the acidic deposits in the and . The waterside surfaces of the boiler will be coated with an alkaline tannate film and the inside of the fire and smoke boxes should be sprayed or painted with a sodium carbonate or sodium bicarbonate solution to slow the corrosion process. If the boiler is stored under cover with the humidity of the air less than 75%, corrosion will be negligible. • Blowing down, by reducing the gauge glass levels by typically a quarter or half, is associated with treatments where antifoaming chemicals are not used as a means of reducing the level of TDS. Blow downs at the main blowdown valve are also used to expel sludge accumulation. Blow down should only be carried out under controlled conditions at the place of maintenance unless a recognised continuous blowdown system is employed.

9. New Boilers When new boilers are procured, it is recommended that they receive water treatment with the very first fill prior to the hydraulic pressure test. This is to prevent rust and help start the formation of protective films within the boiler from the outset. Well constructed and managed boilers suitably treated may be expected to have long working lives. Provided fireside condensation is avoided, all-welded steel boilers thus treated should result in significantly longer tube life, being limited more by erosion than by corrosion.

10. Conclusion Boiler water treatment has become firmly established for steam plant throughout the world. Only the demise of the steam locomotive in every day operation has left a legacy of doubt in the minds of some persons involved with Heritage steam operation. It is anticipated that the contents of this Section has helped to open up the understanding of the benefits of water treatment systems and that universal adoption of treatment will yield savings for owners, maintainers and operators. Water treatment thus offers significant benefits to the maintenance, longevity and safety of boilers.

Issue 02 page 7 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL HGR-B9118-Is02______Boiler Water Treatment

11. References British Standards: BS2486 (1954) The treatment of water for land boilers. BS2486 (1978) The treatment of water for land boilers. BS2486 (1997) The treatment of water for steam boilers and water heaters. BS2455 (1954) Boiler water deposits BS2455 (1973) Boiler water deposits BS1170 (1957) The treatment of water for marine boilers. Journals of the Institution of Locomotive Engineers The solution of some after problems of water softening...... W.L.Topham. P410.J152 Water softening for locomotive boilers...... J.S.Hancock. P468. J198 The influence of the treatment of boiler waters on the maintenance and utilisation of steam locomotives L.Armand. J210 Some aspects of locomotive treatment ...... A.J.Parsons. P572. J257 A brief history of loco. feedwater treatment on the LMRegion...... JS Hancock P573J257 Locomotive feedwater treatment ...... J.S. Hancock. P366. J136 The treatment of locomotive feedwater ...... D.B.H. Pinchen. P404.J149 A brief history of the application of base exchange water softeners to railways...... J.Walter. P463. J195 Corrosion of boiler tubes ...... T.H.Turner J170 Experience with the steel fireboxes of the S.R. pacific locomotives .....M.G. Burrows & A.L. Wallace. P584.J262 ______end of document ______

Issue 02 page 8 of 8 © Heritage Railway Association 2012 The Heritage Railway Association, Limited by Guarantee, is Registered in England and Wales No. 2226245 Registered office: 2 Littlestone Road, New Romney, Kent, TN28 8PL

Top View