Corrosion Mitigation Within Dehydrating Tanks

This report is the accumulation of eight years of experience on only onesmall phase in the business of oil production. It is not intended as a finalreport but rather as a progress report dealing with the internal corrosion ofoil field dehydrating tanks. The corrosion of dehydrating tanks continues to be a problem in the productionof crude oil. The deterioration by corrosion of these tanks falls into threegeneral classifications:Atmospheric corrosion of exterior areas,corrosion of the underside of deck and the rafters and top area of the upperrow of staves in that part of the tank which is known as the vapor space, andcorrosion of the bottom and shell areas, and the steam coils which arenormally immersed in water and thus exposed to the corrosive action of thewater. Atmospheric corrosion is primarily a paint problem, and has been omitted inthis discussion. The corrosion in the vapor space, in this company's experience, which has beenof great concern only in one area, has also been omitted in thisdiscussion. The third, and most troublesome type of corrosion, and the one with which thisreport deals, is that which occurs in the water-exposed areas of dehydratingtanks, and, to a lesser degree, in some stock tanks. The operating temperature of these waters varies from 80'F to 160'F and thesalt counts run from a few thousand to as high as 25,000 parts per million.Corrosion in these tanks occurs in three forms:pits,ringworm type ofattack along the vertical and horizontal bolt seams, andas a generalattack, spread over a wide area. Steam Coils In dehydrating tanks, our experience has been that the steam coils are thefirst to show signs of corrosion, and then the shell and bottom areas. Thisaction is not uniform throughout this company's operations. Some installationshave coil troubles with very little tank trouble, and some show just theopposite. But in the majority of cases the coils are the more seriouslycorroded areas. This may be partly due to the fact that we have tried byperiodic application to keep a protective coating on the interior areas of thetanks, and some protection has been afforded by these coatings. T.P. 2847