In-line Inspection (ILI) tools are widely used to inspect pipeline system in order to determine its integrity by detecting and sizing the geometry of metal loss defects. Following inspection, an integrity assessment is conducted, and the common practice is to determine the remaining strength or safe working pressure (Psafe) of the pipeline by calculating the hoop stress based on the geometry metal loss defects without considering the presence of any other stresses. It has been shown that the pipeline material experiences higher stress based on Finite Element Analysis results, if there are other stresses present i.e. torsion, resulting in lower remaining strength or Psafe. In recent years, a Non-contact Magnetic Tomography Method (MTM) has been introduced as a non-intrusive tool, which is able to inspect ferrous magnetic pipeline without contact.
PETRONAS has successfully utilized the MTM technology to inspect onshore buried pipelines. Being a non-intrusive inspection method, this technology was not affected by the low product flowrate and no changes to the pipeline operation mode was required during the inspection. Further, this inspection method could save considerably in cost compared to ILI whereby the usage of pumps and large volumes of treated water and chemicals were required due to the low flowrate condition. An improved result was captured from the inspection whereby the defect anomalies were categorized into three danger degrees i.e. Rank 1, 2 and 3 in accordance with their technical conditions. The inspection results serve as major input to the Pipeline Integrity Management System (PIMS) to effectively manage the integrity and risk levels of the pipelines.
This paper discusses in depth of the innovative technology using MTM for onshore pipeline inspections.