Application of Hoop Stress Limit State and Predicted Corrosion Rate in Underground Gas Transmission Pipeline Inspection Plan

Abstract

In the transmission pipeline system, decreasing the integrity of the pipe is generally caused by corrosion. Limit state of hoop stress can be applied to determine whether the pipe material is still safe for utilizing below its yield stress. Defining the corrosion rate allowable will be essential in formulating risk of corrosion in the pipeline system. Using an external corrosion rate model generated by soil, the prediction of corrosion rate in every year service life of material will determine the frequency of inspection by adjusting the threshold category. The predicted corrosion rate in every year is as a function of soil resistivity by a factor of coating breakdown and cathodic protection (CP) remaining life. A modified scheme, so called the Inspection-Maintenance-Repair strategy, is an effective method to increase the effectiveness of inspections. The reduction in risk of corrosion is able to extend the inspection plan for several years.