Worst case TLC: cold spot corrosion

Bongkot is an offshore gas field in the Gulf of Thailand in operation since 1992. The sealines have been subjected to top of line corrosion (TLC) since the production start-up. After detection of the first TLC case in this field in 1999, different possibilities were investigated to reduce the corrosion rate to a reasonable value. Batch treatment started in 2000 using double pig^{1, 2} and then Top of Line Corrosion Control Pig (TLCC-PIG^{) 3} has been used since 2004. In 2008 two leaks were experienced on one of the sealines at anode pads and one leak on another sealine close to a subsea flange connection where no coating was applied. In both cases the corrosion was quite localised and took place where the water condensation was high (cold spot corrosion or CPC). Metallurgical analysis showed anomaly neither in the base metal nor on the weld. Accumulated corrosion products on the corroded surfaces prevented corrosion inhibitor to be effective. Laboratory simulations and also predictions confirmed high water condensation rates at the leaking locations. Papers describes operating conditions, corrosion features, protection systems designed to prevent future cold spot corrosion and also presents the results of simulations for cold spot corrosion prediction..