Abstract
Bypass tests of Ø219×8mm 13KhFA, 08KhMFChA, 20-ksh (steel 20 corrosion resistant cold resistant) and Grade steel 20 piping spools were carried out on an oil-gathering line of one of the oilfields in the Stavropol region. Tubing condition was checked after 7, 15, 17 and 23 months of testing. After two years in service no change was found in mechanical properties of the base metal or weldments manufactured from 13KhFA and 08KhMFChA steels. It has been demonstrated that the formation of chromium-containing phase in corrosion products inhibits the penetration of chlorine ions from corrosive media to the surface of metal and thus reduces corrosion rates. Estimated, laboratory and comparison passivation coefficients have been proposed. These coefficients make it possible to predict the level of steel self-passivation with regard to operating conditions of particular oilfields.
Highlights
The use of seamless drawn oil/gas line pipes manufactured from low-carbon chromium 13KhFA and 08KhMFChA steels has significantly improved the service ability of pipeline transportation systems used in the oil industry [1, 2]
General corrosion rate is determined by the thinning of the pipe wall, whereas local corrosion rate is determined by the depth of the pits
A period of steady-state corrosion attack settles in the course of the testing (7 to 23 months) which is determined by the intensity of two interrelated processes: the dissolving of the metal in the corrosive medium and the protective effect of corrosion products
Summary
The use of seamless drawn oil/gas line pipes manufactured from low-carbon chromium 13KhFA and 08KhMFChA steels has significantly improved the service ability of pipeline transportation systems used in the oil industry [1, 2]. In comparison with seamless drawn pipes, they are cheaper, have more stable dimensions and better resistance to corrosion of their internal surface. These advantages transform into benefits, if their base metal and weldments have similar mechanical properties and corrosion behaviour while demonstrating identical changes during their operation. The issue of using welded pipes in oilfields with highly corrosive media still persists. The purpose of this paper is to obtain information on the mechanism and kinetics of the development of corrosion attack/mechanical fracture in welded pipes in the course of their operation in highly corrosive oilfield media
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