Altering the Corrosive Environment

The use of neutralizing amines for acid corrosion in refinery processing is an example of alteration of the environment. The use of filming amines may be thought of as a combination of enviroiunent alteration and a protective barrier, for example, the absorbed inhibitor film supplemented by the sorbed oil film. Chemical treatments employing neutralizers and/or filming inhibitors should be screened in the laboratory and tested in the plant to verify laboratory indications. Such tests are no more error-proof than those on metals or coatings. 

In this respect, the advantage of chemical treatment is that the efficacy of treatment may be followed easily and cheaply in the plant and modifications quickly made if the original treatment is inadequate. Because of the sensitivity, rapidity, and ease of monitoring inhibitor treatments in the field, there is a small likelihood of substantial loss of equipment or performance, or of catastrophic failure. In general, all that is required is the use of a nominal volume of chemical, with appropriate feeding equipment and corrosion-measuring devices. 

Probably one of the greatest economic advantages of chemical treatment over other methods is that the costs of chemicals that must be added continuously are treated for tax and accounting purposes as expensed items similar to maintenance and other operating costs. On the other hand, alloys, and coatings and linings systems usually call for capital outlays of considerable magnitude. 

These expenses are not deducted directly from operating income and hence bear a less favourable tax position. Such generalizations, of course, may vary with individual companies and their accounting systems. Economic evaluation should be performed before selecting the type of corrosion preventive measure, because the success or failure of a corrosion prevention program depends on economic feasibility as well as on technical performance. A plant engineer who recommends a preventive treatment to his management should be conversant with economic evaluation and justification (see also Clause 13 Part 1 and NACE Standard RP-02-72,1972). 

In refineries and chemical plants with highly complex and inter-related processes and equipment, down time because of corrosion failure with concomitant loss in production, and product sales and profits, may be much more important than direct costs of equipment replacement or repair, and the labor to effect them. Such losses can easily exceed the cost of continuous treatment by corrosion inhibitors and anti-foulants. 

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A corrosion inhibitor can function in two ways. In some situations the added inhibitors can alter the corrosive environment into a noncorrosive or less corrosive environment through its interaction with the corrosive species. In other cases the corrosion inhibitor interacts with the metal surface and as a consequence inhibits the corrosion of the metal. Thus, based on the mode of interaction, there are two broad classes of inhibitors. 

Corrosion Inhibitors in Refineries and Petrochemical Plants 211 7.7.3 Altering the Corrosive Environment... 

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