10097 Worst Case TLC: Cold Spot Corrosion

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Product Number: 51300-10097-SG

ISBN: 10097 2010 CP

Author: Yves Gunaltun, Suchada Punpruk, Matina Thammachart and Pornthep Tanaprasertsong

Publication Date: 2010

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One offshore gas field in the Gulf of Thailand has been operated since year 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 year 1999, different possibilities were investigated to reduce the corrosion rate to a reasonable value. Batch treatment started in 2000 using double pig and in year 2004 the Company began using a Top of Line Corrosion Control Pig (TLCC-PIG). In year 2008 two leaks were experienced on one of the sealines at the anode pads and one leak on another sealine close to a subsea flange connection where no coating had been applied. In both cases the corrosion was quite localized and took place where the water condensation was high (cold spot corrosion or CPC). Metallurgical analysis showed no anomaly in either the base metal or on the weld. Accumulated corrosion products on the corroded surfaces prevented effectiveness of the corrosion inhibitor. Laboratory simulations in addition to predictions confirmed high water condensation rates at the leaking locations. This paper describes the 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.

Key words: top of line corrosion, cold spot corrosion, TLC control, spray pig