The Lan Do gas field was developed to supplement the depleting reserve at existing Lan Tay field. It is a crucial development as 22% of the electricity capacity for Vietnam is dependent on gas supply from Lan Tay production facilities. Gas from Lan Do field contains 1.2% CO2 which required corrosion resistant alloy for the flowline. 13Cr was selected at an early stage to take advantage of preferential procurement agreement with the pipe manufacturer. 13Cr can be a cost effective solution for sweet CO2 service. However, there are special requirements that must be addressed for this material to be successfully deployed.

13Cr is known to be susceptible to hydrogen induced cracking resulting from the high potential generated by normal cathodic protection system. Specific industry guidance on the method to address this risk is still lacking. Current solution has been essentially limited to proprietary developed diode controlled anode system. For this project, a proprietary designed diode controlled aluminium alloy anode system was used. The presence of carbon steel fittings, equipment and structures where normal aluminium anodes were attached, imposed a strict requirement for electrical isolation from the 13Cr flowline. Electrical isolation techniques such as monolithic isolation joints were used for the flowline connections, whereas Teflon coating was introduced to isolate the structures. Specific welding details between 13Cr and CRA clad pipes were made to address differing thicknesses between these materials.

Among the challenges in the installation phase was to land an in-line sled structure on a seabed characterized by mounts and valleys. To achieve a level seabed, remedial measure using grout bags dumping was used. The amount of grout bags dumped was large, requiring about 250 m3 of grout bags at a water depth of 185 m, which was rarely done.

This paper describes the innovative approaches taken to address the challenges in engineering the 13Cr flowline and solutions developed to enable construction and installation of the subsea structures on a very rugged seabed. The flowline was successfully installed and received first gas on 7 October 2012.

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