PETRONAS Gas Berhad (PGB), a subsidiary of Malaysia’s national oil and gas corporation, PETROLIAM Nasional Berhad (PETRONAS), processes, transports and supplies natural gas and utilities to petrochemical plants. PGB through its operating division, Transmission Operations Division (TOD) currently operates and maintains the nation’s 2,554 km of high pressure on-shore gas pipelines ranging from NPS 2 up to NPS 48. TOD has been operating the pipelines for more than 24 years and has kept good track record with regard to pipeline safety.
One of PGB’s pipelines is the 24” lateral pipeline which carries high pressure i.e. 45-60 barg dry sales gas to PETRONAS’ customers i.e. power plants in northern part of Peninsular Malaysia, that consume approximately 100-150 million standard cubic feet per day (MMSCFD). The pipeline was commissioned in 2000 and it is equipped with impressed current cathodic protection (ICCP) system for external corrosion protection. Total pipeline length is 28 km with approximately 7 km transverses the Straits of Penang with sea water depth level ranges from 10-20 meters.
From risk assessment conducted for the pipeline, the two highest risks are (i) external corrosion, and (ii) third party. Therefore, to ascertain the integrity of the pipeline based on the risk assessment, PGB performed in-line inspections i.e. high resolution MFL pigging in 2003 and high resolution electronic geometry plus XYZ-mapping pigging in 2007. Both inspections indicate that the pipeline experiences substantial numbers of external and internal metal losses, dents and ovalities. Further to that, immediate and future fitness-for-service (FFS) assessments were conducted for the metal loss, dents and ovalities features. The FFS concluded two main points; (i) the metal losses do not need any immediate repair, and (ii) a number of ‘injurious’ dents require immediate repairs especially in the 7km subsea portion (under Straits of Penang). The subsea repair work had been successfully and safely conducted for the ‘injurious’ dents in October 2009.
This paper will elaborate the overall integrity management program for the 24” high pressure lateral gas pipeline and specifically on the fitness-for-service assessments and predominantly the subsea repair works i.e. the challenges and lessons learnt. It needs to be noted here that the subsea repair works is a critical business decision that the management has taken in order to safeguard the integrity of the pipeline and bottom line of the company.