CENTERPOINT ENERGY GAS TRANSMISSION

Incident Narrative

A FAILURE OCCURRED AT SURVEY STATION 2660+55 IN A RURAL (CLASS 1) PORTION OF CAMP COUNTY NEAR THE COMMUNITY OF CENTER POINT ON FM 2057. THE PIPE SEGMENT WAS TRANSPORTED TO LABORATORY FACILITIES FOR FAILURE ANALYSIS. LABORATORY TESTING RESULTS - STRESS ENGINEERING SERVICES, INC.: STRESS ENGINEERING EXAMINED THE PIPE SAMPLE CONTAINING THE RUPTURE. THE OUTSIDE SURFACE OF THE PIPE WAS COVERED WITH REDDISH-BROWN OXIDE (RUST) DEPOSITS. THERE WAS ALSO EXTENSIVE WALL LOSS OBSERVED DUE TO GENERAL CORROSION AND PITTING ON THE OUTSIDE OF THE SAMPLE. THE INSIDE SURFACE WAS ALSO COVERED WITH LIGHT RUST, BUT NO MEASURABLE LOSS WAS IDENTIFIED. EXAMINATION OF THE CORROSION MORPHOLOGY INDICATED THAT AQUEOUS CORROSION CAUSED THE DAMAGE OBSERVED. THE SUBJECT FAILURE OCCURRED AFTER CUMULATIVE WALL-THINNING RESULTED IN A DUCTILE OVERLOAD. STRESS DETERMINED THAT THE PIPE WAS LAP-WELDED. BASED ON THE MECHANICAL AND CHEMICAL ANALYSES PERFORMED, THE SAMPLE MATERIAL TESTED MEETS APPLICABLE REQUIREMENTS OF API 5L (1949) FOR LAP-WELD PIPE. IT IS BELIEVED THAT THE CHEMICAL AND MECHANICAL PROPERTIES OF THIS PIPE DID NOT CONTRIBUTE TO ITS FAILURE.