Evaluating Anchor Impact Damage to the Subsea Canyon Chief Pipeline Using Analysis and Full-Scale Testing Methods

Abstract

This paper presents findings from a study conducted as part of a joint industry effort involving engineers from Williams Midstream, Stress Engineering Services, Inc., GL Noble Denton, and Saipem America. The purpose of this study was to evaluate the severity of damage inflicted to Williams’ subsea 18-inch × 0.875-inch, Grade X60 Canyon Chief Gas Export Pipeline due to an anchor impact at a water depth of 2,300 feet. The phases of work included an initial assessment after the damage to the deepwater pipeline was detected, evaluating localized damage via finite element analysis based using in-line inspection data, full-scale destructive testing including burst tests, and final efforts included the design and evaluation of a subsea-deployed repair sleeve. The study included modeling Saipem’s repair sleeve design accompanied by full-scale destructive testing. Strain gages were used to measure strain in the reinforced dent beneath the sleeve, that were then compared to prior results for the unrepaired dent test results. The work associated with this study represents one of the more comprehensive efforts conducted to date in evaluating damage to a subsea pipeline. The results of the analysis and testing work provided Williams with a solid understanding on the behavior on the damage inflected to the pipeline and what level of performance can be expected from the repaired pipeline during future operation. After the engineering analysis and testing phases of this work were completed, the deepwater pipeline was repaired.