Abstract
As identified during a public meeting on January 27, 2015, the National Transportation Safety Board (NTSB)(1) performed a study to evaluate the need for improvements to gas transmission integrity management (IM) programs and requirements for gas transmission pipelines. This study has concluded that while PHMSA's (2) gas IM requirements have kept the rate of corrosion failures and material failures of pipe or welds low, there is no evidence that the overall occurrence of gas transmission pipeline incidents in HCA pipelines has declined. Furthermore, the study suggests that of the four different integrity assessment methods (pressure test, direct assessment (DA), in-line inspection (ILI), and other techniques), ILI yields the highest per-mile discovery of pipe anomalies and the use of direct assessment as the sole integrity assessment method has numerous limitations.
The NTSB safety study goes on to conclude there are many limitations to direct assessment, including that (1) it is limited to the detection of defects attributed to corrosion threats, (2) it only covers very short sub-segments of the pipeline, (3) it relies on the operator's selection of specific location for excavation and direct examination, and (4) it yields far fewer identification of anomalies compared to in-line inspection.
In this paper we will examine recent improvements to indirect inspections and DA assessments, and compare the mile per mile anomaly density of ILI to that of the newest indirect inspection technology that is available.
