Monitoring and Maintenance of CP System in MGL

Mahanagar Gas Limited is a City Gas distribution (CGD) company based out of the city of Mumbai and around. MGL currently has around 480 Kms of Steel gas pipelines for transportation of natural gas. The diameters of these pipelines are ranging from 2 '' to 18 '' and almost all are coated with 3 layer Poly Ethylene coating (3LPE). We are installing Permanent Cathodic Protection (PCP) for all commissioned pipelines and Temporary Cathodic Protection (TCP) having a design life of 5 years for un-commissioned pipelines during the projects stage itself. This paper shall basically outline the CP system in MGL along with various practices being followed in MGL to ascertain the effectiveness of CP. MGL has installed various CP assets like CP stations, Diode stations, external ER probes , corrosion coupons to ascertain the CP effectiveness. This paper shall outline the detailed monitoring procedure along with monitoring frequency of all the assets. MGL is also carrying out health adequacy surveys like DCVG, CIPL etc over the steel pipeline network. Few case studies arising out of these monitoring results shall be presented in this paper. (1) Casing carrier short at Taloja Railway crossing. The detailed procedure of monitoring and rectification shall be presented. (2) Case study on CP under-protection at Andheri which was resolved using a flange isolation kit.