A successful approach to application of stress analysis in conjunction with stress corrosion cracking direct assessment

摘要

SCC direct assessment (SCCDA) is a process to improve pipeline safety by assessing and reducing the impact of SCC. It is a cost-effective integrity management complement to the in-line inspection technique and hydrotesting. The reference standard for implementation of SCCDA is NACE SP0204 that presents a methodology for buried steel pipelines. The first and the most important objective of this standard is to prioritize potentially susceptible segments of pipelines and selects specific sites for excavation. In this paper a 16-inch pipeline containing sour gas downstream of the compressor station that was suspected to SCC, was evaluated. Due to the lack of sufficient data regarding the history of pipeline, and because it was not able to pigging, coating flaws that were detected by DCVG, identified as areas susceptible to SCC. All the coating defects were prioritized depending on the severity of defects and environmental conditions and then were excavated. Direct assessment (DA) results indicated that excavation over all coating flaws, is time-consuming and costly. Hence, a pipe stress analysis software was applied along the pipeline as a complementary tool. By comparing the results and their relative compliance with areas where SCC defects were found, it was revealed that considering stress analysis results along with other information like cathodic protection and soil conditions, can significantly increase the accuracy of SCCDA, resulting in reduction time and cost of DA.