Structural integrity of pipelines

Abstract

The acceptance standards given in API 1104 Section 9 are based on empirical criteria for workmanship and place primary importance on imperfection length. Such criteria have provided an excellent record of reliability in pipelines service for many years. Alternative acceptance standards for girth welds are presented in Annex A. The use of fracture mechanics analysis and fitness for service criteria for determining acceptance criteria incorporates the evaluation of both imperfection height and imperfection length. This criteria usually provide more generous allowable imperfection length. This approach is applied to a new gas pipeline, API 5L X70 material, 24 inches diameter and 11.9 mm thickness. The applied methodology is presented to perform failure assessment diagram (FAD) and a sensitivity analysis and safety margins or factors are determined.