corrosion measurement and assessment in acid dosed desalination plants

Des&nation,28 (1979) 89-108 @ Elsevier Scientific Publishing Company, Amsterdam - P&ted in The Netherlands

CORROSION MEAS- NTANDASSEsSMENT IN ACID DOSED DESALINATION PLAN’IS”

K. HARDING AND D. A. BRIDLE

CYXAEA, Atomic Energy Establishment, Winfrith, Dorset (EngLmd)

(Received September 20.1978)

SUMMARY

An investigation of brine chemistry and corrosion behaviour of a wide range of possible construction materials has been carried out under actual service conditions in an acid dosed sea water distiller. A preliminsly report on this work carried out by the UKAEA over the last five years in a multi- stage flash distiller in Jersey CI was presented at the Alghero Symposium in 1976. The programme is now complete and this paper p resenti asynopsis of the result8.

The programme has investigated the corrosion behaviour of some sixteen alloys which have been used or suggested as possible materials for the construction of sea water distillers, Test materials in the form of plain coupons, crevice and galvanic couples, weldmente and stressed specimens, where applicable, were used in the assessment of material behaviour. Additionally, elect&al msistance and ekctropotential techniques were used to assess the behaviour of some materials and to measure inshntaneous corrosion rates and the change of rates under varying operating conditions, particulady during acid cleaniug. The programme examined corrosion under all the conditions prevailing in the plant, that is, sea water inlet; before and after degassing; recirculating brine at various temperatures; vapour spaces and distiuate.

The accuracy and usefuhress of the methods used are examined, together with the importance of the correct siting of probes and coupons. The methods used to determine brine chemistry parametefi are also presented.

It is concluded that carbon steel, alummi - ‘umbrassandnavalbrassare adequate constructional materials for plant life of twenty years provided that strict control of brine chemistry is maintained. More expensive fall back materials are identified which are more tolerant of brine chemistry.

* Presented at the Sixth International Sfrmposium on Fresh Water from the Sea, Las Pahas. Gran Canaria. September 17-22.1978.

so K. HARDING AND D. A. BRIDLE

INTRODUCTION

The production of pure water from sea water in large land-based desalting plants is almost exclusively by some form of distillation, with the multi- stage flash evaporator having become the most popular type of the past 15 years, mainly because of its reliabihty and ease of operation together with flexibility in design and materials.

The operational performance of a distiller is primarily governed by the degree of scaling which occurs on heat transfer surfaces. A number of brine treatments have been devised designed to eliminate or minimise scaling. One such early treatment was the use of polyphosphates which reduce the effects of scaling but do not eliminate it, but with occasional acid cleaning or mechanical sludge removal good operating efficiencies are maintained. This treatment, however, has the disadvantage of limiting the maximum operating temperature to 95°C because of the thermal instability of the additive. On the other hand, a major advantage is the wide tolerance to brine chemistry allowed by this treatment which enables low plant corrosion rates to be easily achieved.

However, with the need to produce water more cheaply, high operational efficiencies are sought which demand high operating temperatures. These can be ahieved by acid treatment of the brine which when carefully con- trolled can effectively eliminate temporary hardness which is the major scale forming agent and allows top temperatures of 12O*C to be reached. The disadvantage of this treatment is the high corrosion of plant material which occurs if strict control of the brine pH is not maintained. Even with the most favourable chemistry control, corrosion in acid dosed plants is more serious than in additive dosed systems because in order to eliminate the temporary hardness the pH must be reduced to less than 7.5.

Designers of acid dosed plants were therefore faced with the problem of assessing what alloys could be used to guarantee an economic life for the plant with wh.at corrosion allowance, and having decided on these fixed parameters, how tight a specification on brine chemistry control needed to be set in order to ensure the guaranteed life was achieved.

fn. 1972 very little data existed on the corrosion behaviour of materials in acid dosed distillers. Furthermore, much of that which was available was kom work carried out in laboratory test facilities or experimental evapor- ators where stricter control of brine chemistry can be exercised than is possible in a commercial plant. The data from such programmes therefore tends to be idealised and whi?st providing valuable information on ranking order can be very misleading when used to assess the actual corrosion allowances necessary to guarantee the working life of a plant. In addition the variation of operating conditions in an actual plant, both hydraulic and temperature, is very wide and it is difficult to predict all the combinations

CORROSION IN ACID DOSED PLANTS 91

to be found in an actual plant, and even more difficult _tO simulate in laboratory tests.

With these considerations in mind, when a large commercial desalination plant was built for the Jersey New Waterworks at Corbiere by Weir Westgarth the opportunity of inst&ing facilities to carry out an extensive programme of corrosion monitoring in an operating plant was requested and agreed to by the Jersey Ne= Vaterworks Management.

The prime concern of a desalination plant operator is water production and he more than most other types of plant operator is under pressure to maintain output, since failure of a public water supply is a particularly sensitive area. production must therefore be maintained even when this means operating for periods under adverse chemistry conditions which will result in increased corrosion of plant materials. Thus our programme of in-plant corrosion monitoring not only provides data from a wide range of plant conditions but from the diverse conditions of operation likely to be found in a commercial plant. The corrosion data obtained from this programme is considered to be most meaningful in assessing the merits of different candidate materials of construction, and providing practical data from which corrosion allowances can be deduced.

This in-plant corrosion assessment programme has been in progress since 1971 operated by the UK Atomic Energy Authority Desalination project on behalf of the programme sponsors: Yorkshire Imperial Metals Ltd, International Nickel Ltd, Jersey New Waterworks, Binnie and Partners and the Department of Trade and Industry. A preliminary report on this work up to 1974/75 was presented at the Alghero Symposium in 1976.

The in-plant exposures were terminated at the end of 1976 and all coupons have now been examined. This paper summarises the work of the programme and presents a synopsis of the results.

PROGRAMME OBJE~CXiVES

These are to measure the corrosion behaviour of the conventional materials used for desalination plant construction such as carbon steel and aluminium brass, together with those materials with potential application in this field but which have so far been considered too expensive to be used extensively in the first generation of plants. This data will provide a basis for assessing the likely value of these alternative materials.

The influence of brine chemistry on corrosion has also been studied with a view to enabling operating procedures to be developed which will allow the cheapest combination of structural materials to be used and still achieve a satisfactory plant life.

92 K. HARDING AND D. A. BRIDLE

DESCRlPTION OF THE JERSEY DESALINATION PLANT

The plant in which this work has been carried out is a typical example of a multi-stage flash evaporator of rectilinear construction. The plant was built by Weir Westgarth Limited for the Jersey New Waterworks Company Limited who are the owners and operators. The function of the plant is to supplement the island’s water supply during the summer and autumn of each year when ramfall is low and local demand, augmented by the influx of tourists, is high. The plant was commissioned in the summ er of 1970 and has operated for a Ma.l of 20 months in the 7 years up to 1976. Fig. 1 shows a histogram of water production with respect to time. During the winter the plant is washed out with towns water, drained and dried. This allows easy access to the plant for long periods which facilitates ease of removal and reinstallation of large numbers of samples throughout the plant.

Plant output at rated capacity is 6830 m3 /day. Feed is clean sea water, acid dosed to remove all but 5 to 15 ppm bicarbonate alkalinity. Feed flow is 13660 m3/day and brine is rejected at 6830m3/day at twice sea water concentration. The feed after acid addition passes through an air blown decarbonating tower before entering the first of three heat reject stages where it is mixed with recirculating brine and is heated and degassed by the bigb vacuum of these low temperature stages. Brine flow is 2290m3/ hour and after removal from the last heat reject stage at 35OC it is returned

1975 (72x10’

1976 (207x10’ galls)

Fig. 1. Jersey MSF plant - total water production 1970-1976.

CORROSION IN ACID DOSED PLANTS

t

e

-

93

K. HARDING AND D. A. BRIDLE

through the condensers of 44 heat recovery stages to the brine heater where its temperature is raised to 116°C. From here the hot brine flashes through 47 stages to the reject point.

Recovery and reject stages are arranged in two decks, one above the other. Condensers are of cross tube pattern and access to water boxes at each stage is possible through bottom entry manholes. This not only permits detailed inspection of water box internal surfaces and tube ends at close intervals over the whole temperature range, but in selected stages allows exposure of racks of corrosion coupons in flowing brine. Similarly, access is available to each flash chamber. Figure 2 shows a flow diagram of the plant. A summary of the design parameters and constructional materials is given in Table I below.

TABLE I SUMMARY OF PLANT DETAILS AND MATERIALS OF CONSTRUCTION

Plant components Brine heater Recovery stages Reject stages

Number of stages Number of tube passes per stage

Number of tubes per pass Heating surface (m2 ) Brine velocity, m/s

1 44 3 2 1 3

548 598 135 636 15300 1020

1.75 1.60 1.48

Plant component

Evaporator shell

Material

Mild steel to BS 1501. Coated with chlorinated rubber plant and epoxy (dependent on temperature).

Water boxes Brine heater Moue1 clad steel Heat recovery stages l-10 (> 93°C) Monel cIad steel Heat recovery stages 11-44 (< 93OC) Mild steel coated

with chlorinated rubber paint Heat reject stages 45-47 Mild steel rubber lined

Tube plates Rolled naval brass to BS 1541

Heat exchanger tubes Aluminium brass to BS 1541

Separators Monel mesh

CORROSION TEST PROGR,AMME

The initial corrosion programme was set up with a total of thirteen alloys which included all the materials used in the Jersey plant construction for

CORROSION IN ACID DOSED PLANTS

reference, together with materials considered as possible substitutes in the event of serious materials failure occurring on the plant.

At the end of the 1970 operating period the aluminium alloys were all removed and further testing of these alloys stopped because of severe pitting which indicated that these alloys would be of no value under the conditions encountered in the Jersey plant.

Again, after the 1971 operating period, the corten low alloy steels were withdrawn from the programme because the corrosion behaviour of this alloy was, for all practical purposes, identified with that of mild steel.

In time for the 19’72 operating period the scope of the programme was increased by the addition of further copper based alloys, the chromium containing IN 838 80/20 copper nickel and IN 848 70/30 copper nickel, together with Yorcoron and Ampco alloys and the duplex alloy Ferralium - an austenitic precipitation hardening stainless steel. Table II lists all the alloys tested together with their chemical compositions.

All specimens were cut from sheet material to a standard size of 75 x 25 x 3mm and were mounted on stainless steel frames, being insulated from the frames and each other by Teflon washers. Most materials were present in four forms: plain coupons, welded coupons, crevice specimens in which two coupons of the same material were mounted together without an insulating washer, and galvanic couples -here the material coupon was mounted in contact with its dissimilar partner, usually carbon steel or brass.

SPECIMEN LOCATION

Sets of specimens containing all the materials under test in all the four types of test form were located in selected flash chambers and brine boxes to give a representative cross section of conditions throughout the plant. Test frames of coupons housed in the flash chambers were exposed in the flashing brine; the splash zone and the vapour region (above the demister Pads)-

Table III shows the stages and regions in which specimens were exposed and gives the operating temperatures associated with each location.

In addition to the coupons which provide integrated corrosion data, a number of corrosion probes of both the electrical resistance type (Corroso- meter) and the linear polarisation type (Corrator) which can provide differ- ential and instantaneous corrosion data were also installed. These were located fairly uniformly around the plant at the start of the programme but dwindled in numbers as the programme matured until only the top temperature point and other points of highest corrosion such as WB 47 and FC 45 were monitored using probes towards the end of the programme.


TABLE III

Stage Regi0n Temperature OC

1 Flashingbrine 114 Splashzone 114 Vapour 114 Waterbox 110 Waterboxlj2 108

23 Flashingbrine 76 Splash zone 76 Vapour 76 Waterbox 72

44 Flashingbrine Splashzone Vapour

:; 37

45 Flashingbrine SpIashzone Vapour

35 35 35

*4-i Waterbox 28

*Note that stage 47 water box is fed with untreated sea water.

BRINECHEMISTRY

For the results Gem a corrosion programme to be generally applicable it is essential to have detailed knowledge of the environment to which the test specimens have been exposed. As discussed earlier, in an operating plant the brine chemistry can sometimes be outside that specified for many reasons but yet the plant must continue to operate - the Jersey plant is no exception. Monitoring, and with it control, of the brine chemistry has been steadily improved during the period of the programme as both the plant and corrosion programme operators learned by experience. Comprehensive records of the brine chemistry have been maintained which enable detailed comparison of corrosion behaviour to be made from one exposure period to another, despite variations in brine chemistry. A summary of the major brine chemistry parameters is given below.

Residual alk+linity and pH In common with acid dosed sea water desalination plants the feed is acid

dosed to remove the temporary hardness to give a residual alkahnity (RA)

98 K. HARDING AND D. k BRIDLE

of less than 20 ppm (CaCO, ) in the recirculating brine. During the first years of operation the operating specification for RA was 10-20 ppm; later this was reduced to 5-15 ppm which should give a pH of 7.3-7.8. However, because the decarbonator is not 100% efficient, the feed brine to chambers 45,46 and 47 which act as degassers is usually about 6.9. Degassing in these chambers then results in a rise in pH to between 7.4 and 7.7 for the recirculating brine as the remaining CO1 is drawn off by the vacuum.

Although the reduction in alkalinity minimises alkaline scale formation it does not entirely eliminate it and some alkaline scale is formed on the heat transfer tubes. In addition, some deposition of iron oxides also occurs. These deposits both reduce heat transfer efficiency and increase the hydraulic resistance of the circuit which impairs plant output. Remedial action up to 1972 was periodic acid cleans, i.e., extra acid dosing, to give reduced recirculating brine pHs of about 3 approximately once a fortnight. In 1973 the practice was changed to a daily “mini clean” in which the pH is reduced to between 4 and 4.5 for one hour each day. Occasionally it becomes necessary to carry out a more aggressive acid cleaning operation. In this case the pH is reduced to between 3.5 and 4 for between lo-12 hours. Typically two

such operations will be necessary during an operating period.

Dissolved gases

The importance of maintaining low levels of oxygen and carbon dioxide in the brine in order to minimise corrosion has long been recognised. However, the m-actical problems of operating a large plant under vacuum and maintaining it leak free should not be underestimated. On the Jersey plant periodic measurements of dissolved oxygen and, in more recent years, for dissolved carbon dioxide are made. Fig. 3 shows the typical range of concentration of these throughout the plant. Decarbonation takes place in

MLC UD lee4 frm decmbcn,tor Iappm 3nqmxlme- COl,

Fig. 3. mpical dissolved oxygen and carbon dioxide concentrations in the brine.


an air sparged tower after acid injection of the raw feed brine but this tower is only 90% efficient and the remainder of the CO2 must be removed by the heat rejection sections, chambers 47-45, which being under the Eghest vacuum also act as a degassing section. Towards the end of an operating run leaks tend to develop in the seals and oxygen levels in the flash chambers increase in an erratic manner.

Copper and iron concentrations During normal operation the copper found in the brine varies with tern-

perature, i.e., increases up through the water boxes, due to corrosion pick up through the heat exchanger lubes, the largest copper input coming from the heat input section, then falls on passage through the flash chambers. Part of the copper is soluble and part insoluble; the ratio of soluble to insoluble varies throughout the plant and appears to be connected with the levels of dissolved carbon dioxide_ There is also a correlation between the measured total copper in the brine at FC No 1 and the measured total corrosion of the copper containing components in the plant.

III the case of iron there is no single correlation, the iron is predom~~tly in suspension and the quantities are not at all related to system corrosion. Most of the products of iron corrosion are precipitated in situ to build up thick but unprotective layers of oxide on the flash chamber walls.

On acid cleaning the picture changes; all the copper now appears in solution. At any pH below 6.0 the copper concentration reflects reasonably accurately the rate of copper ahoy corrosion. Similarly for iron, as the pH is reduced more iron is taken into solution, although large amounts are still dislodged as suspended insoluble material even at pH 4.0.

Our interest in iron and copper in the brine !s related to seeking cor- relations with total corrosion and in the case of copper its inCuence on the corrosion of other components, particularly steel. Deposition of copper metal by displacement has been observed to take place on probes and coupons during acid cleaning and may occur during normal operation. Analysis of corrosion scales shows copper both as oxide and metal to be an important constituent, usually in the range of l-696 but occasionally up to 10% in localised regions.

CORROSION RESUZTS

At the end of each operating period ah the coupon racks were removed for the retrieval of those coupons due for examination and the safe storage of those which were to be re-exposed. In any series of coupons some were exposed for single periods and others for multiple exposure periods between examination. The coupons being ex amined were descated using inhibited acid and soft brushing prior to weight changes being measured, followed by

100 K. HARDING AND D. k BRIDLE

visual examination for pits and cracks. Occasionally dye penetrant was used to help look for cracks on the high alloy steels. A limited number of coupons were sectioned and examined by microscope. Data from con&or and corrosometer probes is collected during the operation of the plant by taking periodic readings manually in most cases; for a few strategically placed probes readings were taken continuously and displayed on chart recorders.

The information collected from the full programme has been assembled in tabular form and assessment in detail reported to the sponsors, but is too voluminous to present here.

Summaries of part of the data are presented in Tables IV to VII and I;‘@. 4 and 5, which illustrate some of the major conclusions drawn from the programme.

IO 20 30 40 50 60 70

Doys operahop

Fig. 4. Mild steel corrosion flash chamber 23 data from corrator/corrosomet.er coupons (brine).

3

- 0.5

,” E 16- -0.4 14-

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IO 20 30 40 50 60 70 Days operation

and

Fig. 5. Mild steel corrosion water box 47 data from corrator/corrosometer and coupons.

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Carbon sfeet Corrosion rates for carbon steel in the Jersey plant are clearly seen to be

high. A major cause of this is the frequent acid cleaning operations as illustrated in Fig. 4 where the instantaneous corrosion rates for normal and acid conditions are seen to differ widely from the average value obtained from coupons. This wide divergence can be compared with the close agree- ment illustrated in Fig. 5 obtained for similar measurements made in water box 47 which is not subjected to acid cleaning_

Table IV shows carbon steel corrosion data from plain, crevice and weld coupons for the last three operating periods and illustrates the range of corrosion rates in the various plant positions. Table V shows carbon steel data for the last operating period, 1976, Erom coupons and probes.

Copper altoys In comparison with carbon steel, these alloys show little significant

corrosion_ Table VI gives average corrosion rates measured over the whole programme for all the copper alloys, for comparison. Corrosion of all these alloys in ah conditions tested was almost exclusively uniform, some dezincification of brass was observed but on all other copper alloys only occasional small pits have been noted, most of which have been shown to be due to inclusions.

Table VII gives average weight loss measurements for the austcnitic, duplex and high nickel alloys in the programme. Carbon steel and titanium rates are also given for comparison. The apparent excellent performance of the austenitic alloys given by weight loss measurements is not confirmed by closer examination, all cotlpons of these alloys exhibited pitting but of widely differing severity. On all coupons pitting associated with crevices was noted, i.e., under the insulating washing, most coupons also showed pits not associated with crevices, some up to 2 mm deep after a few months exposure. 321 was worse than 316. Ferralium coupons however showed only slight pitting, always associated with crevices. Incoloy, Monel and Titanium coupons showed no pits and only very low uniform corrosion.

Aluminium alloys Both types of aluminium exhibited erratic corrosion behaviour. In some

specimens little corrosion occurred whilst in others severe pitting attack resulted in full penetration of 2.5 mm thick sections after only a few months exposure. It was concluded that this behaviour was due to variable copper contamination and that aluminium alloys would be unsuitable for use in a system containing copper. F’urther testing of aluminium alloys in the Jersey plant was therefore inappropriate and these materials were withdrawn from the programme.

10s K. HARDING AND D. A. BRIDLE

DISCUSSION

Carbon steel Corrosion of carbon steel under the Jersey Desalination Plant conditions

can be classed as severe, being equivalent to 1-2 mm penetration per year. A high proportion of this corrosion results from the need to acid clean at regular intervals to maintain heat transfer efficiency. However, the corrosion rate for normal operation at about one third of the total integrated rate, 0.3-0.6 mm per year, is still too high for comfort and there is clearly a need to find an acceptable alternative alloy to carbon steel for use in acid dosed sea water distillers. Such alloys are being developed in programmes co- ordinated by the EEC in Austria, Holland and France. Alternatively, other methods of brine chemistry control could be used and have been proposed by Ciba Geigy (Belgard EV).

In summary, our work has demonstrated that under the Jersey plant conditions corrosion of carbon steel is uniform and high, no enhanced corrosion in crevices occurs, welds are preferentially attacked, particularly metal arc welds which should be avoided in preference to argon arc. Sig- nigicantly enhanced corrosion effects have been seen in regions of high turbulence even though the net flow rate in these areas is below what is normally considered acceptable, ie., 2 metres/s, local effects on levels are very significant.

Corrosion in the vapour regions of the distiller is by comparison very low, but is much higher in the heat reject sections which act as degassers.

Copper al!oys The observed corrosion rates for all copper alloys in the Jersey plant is

acceptably iow, notwithstanding the corrosive environment for carbon steel. Naval brass shows the highest corrosion rates but has been used for all the tube plates and has performed welI even in the monel lined water boxes. Coupon tests have confirmed this observation. Aluminium brass corrosion rates in all parts of the plant have demonstrated good performance and this is confirmed by the actual tubes in the plant. This is especially the case in the vapour region. It should be noted that the sea water feed to the Jersey plant is particularly clean.

Of the alloys tested, apart from Monel (strictly a nickel alloy), none shows outstanding performance over the full range of conditions. In general each has a situation where it performs best which indicates that for best performance under difficult conditions it would be advisable to select several alloys using each in the situation where it performs best.

Localised corrosion has not been observed in any of the alloys except Naval brass where some slight dezincification has been noted. Enhanced attack in crevices is also absent even in the vapour regions.


Stainless steel The high resistance to general corrosion exhibited by the austenitic steels

is accompanied by intense pitting attack even on plain coupons which is extremely random. However, the attack is so intense, particularly on 321, that the use of this material for most applications cannot be recommended. 316 is subject to the same form of attack, although it is more resistant and is of doubtful value under these conditions.

The duplex alloys, Ferrahum L and F, offer much greater resistance to pitting attack, although shallow pits were observed in crevices. However, performance was good and these materials could be recommended for applications where stainless steels would normally be used, e.g., pump and valve bodies.

Nickel alloys The two high nickel alloys tested, namely Monel K and Incoloy 825,

have exhibited excellent corrosion resistance. Failures from the use of these materials either from uniform corrosion or locahsed attack is highly im- probable. This is confirmed by the Monel liners on the Jersey water boxes 1 to 10 and the heat input vessel which have given excellent service.

Titanium This material is also outstanding in its performance, the test specimens

have come through 5 years of exposure without significant change. Titanium can be recommended for any application where its cost can be accepted.

Corrosion data The main method of obtaining corrosion data in this programme has been

by coupons. For most materials at least 3 specimens of each type were installed at each location_ The corrosion rate for that location and that material for that operating period being obtained by averaging the three results. In addition results from fresh coupons exposed for single periods and coupons exposed for multiple periods have been averaged together to give

composite corrosion rates. Assessment of data from specimens exposed for both single and multiple test periods between examination has led to the conclusion that corrosion on carbon steel is not significantly influenced by the presence of a corrosion film, i-e., base metal coupons corrode at sub- stantially the same rate as coupons coated with a thick oxide layer provided the exposure period exceeds 20-40 days.

Despite the observed variation in brine chemistry from year to year which must produce variations in corrosion rates, the overall corrosion picture which has emerged from the programme is now quite consistent.

Corrosion rates and total corrosion have been measured for two materials, carbon steel and ahuninium brass, using corrosometer and corrator probes.

108 K. HARDING AND D. -4. BRIDLE

In general the results obtained using all three types of measurement can be very good, see Fig. 5. However, there have been some notable exceptions which can be disconcerting until explained. One major course of discrep- ancy is caused by copper plate out on both aluminium brass and carbon steel probes. This gives rise to apparent low corrosion rates, only to be followed by very high changes when the deposited material is dislodged or results in pitting attack and premature probe failure. A second cause is badly sited probes in high local turbulence regions indicating apparent high rates of corrosion not subsequently substantiated from coupons not so affected located close by.

The importance of correct location of probes with respect to their associated coupons cannot be over emphasised. Also, if comparable results are to be obtained, periodic maintenance of the probes to check for copper deposits and remove them if required. The use of on-line probes has been found to be invaluable in providing ancillary information on corrosion during abnormal plant operation, e.g., acid cleans, which coupons could not supply. Also, plant operators have learned to trust and come to rely on the direct indication of corrosion which they give.

CONCLUSIONS

The five year corrosion test programme in the Jersey acid dosed sea water distiller is now complete. Approximately 6000 samples of some 20 alloys have been involved. The results will provide a data base from which the likely behaviour of any of the alloys tested in any distiller situation can be assessed and the most suitable chosen to fuliil any requirement.

In general the programme has shown that ahuninium brass tubes and Naval brass tube plates are perfectly satisfactory materials for heat transfer applications but that carbon steel is not fully adequate for the job without protection, either by cladding- and here Monel has been shown to be satisfactory - or by further improvement in brine chemistry control.

ACKNOWLEDGEMENTS

The authors wish to express their thanks to Mr R. Berry and his staff who were responsible for setting up the programme; the Jersey New Water- works Management for permission to use the distiller and the plant operators for their assistance with the mechanics of the operation. Thanks also to the staff at AEE Winfrith for their work on specimen examination and chemical analysis, and finally to the programme sponsors - Yorkshire Imperial Metals Ltd, International Nickel Ltd, Jersey New Waterworks, Department of Trade and Industry, and Binnie and Partners for their financial support.

‘Yorcoron’, ‘Yorcalbro’, ‘Incoloy’ and Ferralium are all registered Trade names. The authors wish to thank Ampco Metal Ltd. and Langley Alloys Ltd. (Ferralium) for permission to publish data relating to their products.

corrosion measurement and assessment in acid dosed desalination plants

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