Non-Contact Magnetic Tomography Method MTM Inspection for Re-Instatement of a Decommissioned Buried Pipeline

The Magnetic Tomography Method (MTM) has been introduced as a non-intrusive inspection technique capable of inspecting ferromagnetic materials such as carbon steel pipeline without any contact. A buried main pipeline in one of PETRONAS's operating countries that had been out of service for more than 8 years needed to be inspected prior to being re-instated. This paper discusses in detail how this innovative MTM technology was used to successfully inspect a decommissioned buried pipeline and safely re-instated the pipeline operation. The MTM inspection covered 172 kilometres of buried pipeline, including the calibration work which involved direct assessment methods. The danger degrees such as Rank 1, 2 and 3, as well as the safe operating pressures, Psafe along the entire pipeline were determined using the MTM results of Risk Factor F in accordance with MTM technical approach. Direct assessment findings were consistent with the MTM inspection findings, as the technology detected all of the anomalies discovered by the direct assessment methods. MTM inspections of decommissioned buried pipelines are proven since they are reliant on the residual self-magnetic leakage field (SMLF) in the pipeline and do not require any intrusive works. Being a non-intrusive inspection method, this technology was not affected by the low pressure & low flowrate, and no changes to the pipeline operation mode was required during the inspection. Further, this MTM inspection method was not affected by the stalled pigs inside the pipeline, as this inspection method was non-intrusive. The inspection results serve as major input to the Pipeline Integrity Management System (PIMS) to effectively manage the integrity and risk level of the pipeline.