WORST CASE TOP OF THE LINE CORROSION: COLD SPOT CORROSION

摘要

One offshore gas field in the Gulf of Thailand(1) has been operated since year 1992. The sealines havernbeen subjected to top of line corrosion (TLC) since the production start-up. After detection of the firstrnTLC case in this field in year 1999, different possibilities were investigated to reduce the corrosion raternto a reasonable value. Batch treatment started in 2000 using double pig1,2 and in year 2004 thernCompany began using a Top of Line Corrosion Control Pig (TLCC-PIG)3. In year 2008 two leaks werernexperienced on one of the sealines at the anode pads and one leak on another sealine close to arnsubsea flange connection where no coating had been applied. In both cases the corrosion was quiternlocalized and took place where the water condensation was high (cold spot corrosion or CPC).rnMetallurgical analysis showed no anomaly in either the base metal or on the weld. Accumulatedrncorrosion products on the corroded surfaces prevented effectiveness of the corrosion inhibitor.rnLaboratory simulations in addition to predictions confirmed high water condensation rates at the leakingrnlocations. This paper describes the operating conditions, corrosion features, protection systemsrndesigned to prevent future cold spot corrosion and also presents the results of simulations for cold spotrncorrosion prediction.