Abstract
The Bongkot field is a high CO2 (>20%) wet gas field located in the Gulf of Thailand. Thirteen infield carbon steel sea lines are laid in 80 meters of water. The lines sizes are 14” to 22”. Almost 2/3 of the lines circumferences remain in contact with sea water; 1/3 buried on the sea bed by natural burial. The average flowing temperature at wellhead is about 90°C but declines rapidly to almost ambient temperature after a few kilometres. The major part of heat transfer through the pipe wall takes place along the first 500 meters after touch down. Due partial line burial, heat exchange takes place on the upper half section in contact with relatively cool sea water current (18 deg C) causing severe water condensation on the internal pipe surface. The flow regime is stratified at the inlet of the dogleg. Top of Line Corrosion (TLC) is expected along the first few kilometres. Some of lines were inspected by Magnetic Flux Leakage (MFL) inspection tools and severe TLC was detected. Being confronted with the decision to de-rate the pipeline or even worse to repair some corroded sections, the authors have tried to obtain accurate remaining wall thickness measurement by other mean than Magnetic Flux Leakage pig. IRISPig was developed and the new inspection of one of the lines shown only 50% of the thickness loss measured by MFL.
