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He may have to go further and carry out T is often mistakenly thought that the as a guide), or whether it is a new plant but laboratory tests, or even pilot tests on fight against corrosion is exclusively, or similar to one erected elsewhere (in which case the experience available must be miniature models. largely, a problem of maintenance. That judiciously adapted to local circumstances), The final choice from a short list of this is not so is a point strongly emphasised or, finally, whether it is an altogether novel possible solutions will depend on the price by a Belgian expert, R. de Smet, who, in the May 1954 issue of Industrie Chimique plant where no previous experience is and on the importance in each case of Beige, surveys corrosion from a plant available. certain physical properties, such as weld- designer's viewpoint. ability, mechanical strength, abrasion re In trying to predict the effects of cor sistance, behaviour when subjected to im rosion, a distinction must be made between It is being increasingly appreciated that portant temperature fluctuations, possi 'internal corrosion,' inherent in the process problems of corrosion must be taken into bility of in situ repairs, etc. account at the design stage in just the same itself, and 'external corrosion,' caused by way as other operational conditions, such atmospheric agents or by gases and vapours In making the choice certain general as pressure and temperature. As new pro of adjacent installations. In the former principles must be kept in mind. It is case, anti-corrosive measures may include often worthwhile to make the walls thicker duction techniques with higher tempera suitable modifications of the process itself, than would be strictly necessary for the tures and higher pressures are developed or the use of selected corrosion-resisting sake of physical and mechanical stresses. the corrosion problem grows. materials, or, finally, the creation of a Welds must be smooth and well designed As regards maintenance, corrosion can barrier between the corrosive fluid and the so as to avoid occlusions and cavities. be the decisive factor, since the degree of base metal of the machinery; in other Drainage systems must ensure complete destruction can soon become so high as to words, the insertion of a protective lining removal of liquids which might otherwise make the cost of maintenance prohibitive. of suitable material, such as plastics, rub cause corrosion. Angles and cavities where It is no exaggeration to state that, in the ber, cement-bound materials, special metal moisture is liable to concentrate must be heavy chemical industry, corrosion repre alloys, etc. avoided also in structural parts where sents at least one-third of the total main tubular shapes rather than angular shapes tenance cost, so that a close study of a Protection against external corrosion will are preferred. corrosion-reducing design can be highly be considered at the design stage; it may, rewarding. Zones subject to mechanical tension are indeed, be a vital factor in deciding on the particularly vulnerable and should be site of the works in relation to other plants, However, there are important difficulties specially protected against corrosion. Con prevailing winds, etc. Waste liquids giving to overcome. For one thing, there are no tainers, etc., lined with brick or the like off aggressive vapours must be disposed of precise formulae permitting a prediction of must be so designed that moisture cannot the destructive effect of corrosion in the in the shortest possible time and along the infiltrate between the lining and the wall same way as the effect of physical and shortest possible route. Those parts of the proper. Pipes conveying corrosive fluids plant liable to give off particularly aggres mechanical stresses can be predicted. should preferably be placed above ground sive vapours should be placed as far as Secondly, the desirability of taking suitable so that any leakage can be promptly de possible out of harm's way. These seem anti-corrosion measures even at the design tected. On the other hand, those pipes ingly elementary precautions are still all too stage is sometimes overlooked in the some which do not convey corrosive fluids should what short-sighted endeavour of the plant often neglected. themselves be protected by being buried in manufacturer to secure the order, and of the ground and covered with a coating of the client to buy cheaply. Also, the special Som e simple rules bitumen or the like. In special cases, materials known to be best suited for a In order to make a proper selection from cathodic protection is desirable. In other particular purpose may not be available among many anti-corrosive measures which cases, galvanic corrosion may have to be at the right time for various reasons. might be taken, the plant designer will taken into account. Again, especially with novel types of normally have to carry out certain pre The part played by the designer does plant, the effect of corrosion may be under liminary studies. He must, of course, not end with the erection of the plant. He rated by the designer because as yet there acquaint himself with the relevant hand books and specialised literature on the cor will still have to advise the production is not enough experience available and rosion problems concerned, with the stan department on specific measures of cor corrosion generally only becomes manifest rosion protection to be taken either as part dard specifications (if any) applicable to when it is too late to alter the design. Any of normal maintenance routine or in case attempt to predict this effect must take into his case, and with the specifications of the of accidents. E.R. account not only the nature of the raw makers of special anti-corrosive materials. materials and that of the finished product, but also the intermediate products and by products. Even with the same material a change in conditions, such as speed, pressure and temperature, may make all the difference to the corrosive effect and Bronz e alloys are among such changes, which may be deliberate or th e corrosion-resisting metal s made by J. Stone due to some fault or breakdown, must also & Co. (Charlton) Ltd. In be taken into account. A case in point is this view of part of the the contact process of sulphuric acid pro Bronz e Casting Division, duction, where stoppage may cause grave mould s are being removed after drying in a G.E.C. corrosion damage which need not be feared infra-red plant. Th e moulds with normal production. In other cases, ar e given a firm surface temporary working beyond the normal and freed from air pockets rated capacity may have a similar effect. by this method of drying. Beside s 'B.H. bronze,' J. The measures to be taken by the plant Ston e & Co. manufacture designer will vary according to whether the 'Superston ' and 'Hydro- nalium ' corrosion-resistant plant is to form an extension of an existing alloys . plant (so that local experience can serve 246 CORROSION TECHNOLOGY, September 1954
Anti-Corrosion Methods and Materials – Emerald Publishing
Published: Jul 1, 1954
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