Abstract
Three major corrosion problems encountered in pipe line operation are considered. Experience with the various corrosion control methods is described and the economics of their use is examined.
Internal Corrosion in Sour Crude Oil Pipe Lines— For controlling internal corrosion in sour crude oil pipe lines, corrosion inhibitors, regular scraper runs, internal coatings, concrete lining, asbestos-cement pipe and plastic pipe all are effective and economical. Cost comparisons for two average sour crude oil gathering lines indicate that 1) in general, concrete linings and corrosion inhibitors appear most economical in the longer, larger lines while concrete linings, internal plastic coatings and plastic pipe appear most economical for the shorter, smaller lines, but, 2) all of the protective measures provide major savings—from at least 9 cents to as much as 25.5 cents per foot of pipe per year.
External Corrosion of Oil Storage Tank Bottoms —Slightly more than 5 percent of the unprotected oil storage tank bottoms in a large pipe line system fail each year as a result of soil corrosion. Cathodic protection effectively controls corrosion at an average installation cost of $410 per tank and an average total operating expense of $62 per tank per year. This installation cost is equivalent to about 3 percent of tank bottom investment; the total annual operating expense is equivalent to about 1¼ percent of one repair job. Protection of all remaining unprotected tank bottoms in the system would have an indicated payout of 1½ years; the total annual operating expense of such protection would amount to about 25 percent of the present annual direct cost of tank bottom repair.
External Pipe Coatings and Cathodic Protection— Substantial coatings supplemented with cathodic protection are used generally for preventing external corrosion of buried pipe lines. Examination of the relationship between coating practices and costs and cathodic protection requirements and costs indicates that: 1) For minimum total cost coatings are needed; 2) Even the best pipe line enamel coatings are not free from imperfections and require supplementary cathodic protection for full protection of the pipe; 3) The cost of cathodic protection on reasonably well-coated lines is so small that the large expense and effort required to secure more than reasonably good coating jobs are difficult to justify. Items of such expense include coating reinforcements, complete holiday detector inspection, rigid insistance on holiday-free construction, rock shield, ditch padding.
