The Corrosion, Cleaning, Inspection And Repair Of Storage Tanks In Crude Oil Service

Abstract

Abstract In the absence of serious failure it is possible that the inspection and maintenance of crude oil storage tanks can be permitted to fall below the optimum level. Following a catastrophic light product tank failure, the Bahrain Petroleum Company (BAPCO) carried out a very extensive cleaning, inspecting and repair programme to 250 tanks, including several in crude oil service, over the last six years and describe the lessons learnt. Introduction In November 1972, a 20,000 bbl. tank constructed in 1949 containing 19,000 bbls. of Pbs treated naphtha ruptured through the upper four shell courses. The released naphtha was ignited when some part of the failed tank struck an overhead power line. The resulting fire destroyed several power line. The resulting fire destroyed several other tanks and a major section of refinery pipe-way including a transfer pumphouse. There were, pipe-way including a transfer pumphouse. There were, fortunately, no fatalities. It was concluded after the subsequent investigation that there were shortcomings in inspection methods and the attitude towards tank maintenance and that a substantial backlog of tank inspection and repair existed. An extensive Inspection and Repair Programme was commenced in 1973 which is still ongoing. During this period some 250 tanks including several in crude oil service ranging from 2000 to 625,000 bbls. capacity were thoroughly inspected. A considerable amount of repair work was found to be necessary, much of it being unexpected and of a very major nature. The tankage in Bahrain has been installed for a longer period than most in the Middle East and is in a coastal corrosive environment. Others operating in this and similar areas, may soon find their tankage to be in a worse condition than realised and should benefit from this paper which is intended to pass on the current methods and procedures which are a direct result of experience procedures which are a direct result of experience gained during the extensive inspection and repair programme. programme. The prime concern of the paper is tanks in Crude Oil Service but the most significant lessons learnt with tanks in other services are included for the interest of those with Refining/Marketing operations in addition to production. CORROSION Corrosion, both internal and external, of oil storage tanks has been recognized in Bahrain to be a problem for many decades - requiring considerable expenditure in terms of effort and funds to rectify. The more thorough methods of preparation for inspection, recently introduced, have however, revealed that the degree of corrosion has been underestimated in the past. During the recent tank inspection and repair programme 757 of tanks of various services were programme 757 of tanks of various services were found to require the replacement of one or more shell rings, or all (or most) of the floor, or all (or most) of the roof. Several tanks required a combination of two or three of these repairs. All crude oil tanks were found to require major floor and/or roof repairs. The tanks used in the field oil gathering and transfer systems are small, cone roofed. They were constructed originally from bolted, thin gauge mild steel plate. Internal corrosion, taking the form of pitting and general metal loss has been experienced on roofs, shells and floors. Severe roof corrosion has been combatted by a change in material to aluminium. Corroded shell plates have been replaced in kind when necessary, otherwise have been coated internally with glass reinforced plastic coatings over the whole surface. Floors have been renewed using thicker steel plate and have been protected top side by using glass reinforced plastic protected top side by using glass reinforced plastic coatings (G.R.P.).