Yefan Su

Current studies on fatigue crack initiation in pipelines remain relatively limited. Existing frameworks are confronted with issues including difficulties in crack monitoring and limited consideration of intragranular short-crack propagation. To address these issues, a framework was proposed for predicting fatigue crack initiation life in pipelines with girth welds. The proposed framework incorporates full-scale testing, temperature field simulation and microstructural evolution analysis to overcome limitations in crack measurement and microstructural characterization. In addition, intragranular short-crack propagation has been taken into account in the proposed framework. The proposed framework predicts the fatigue crack initiation life through multiscale coupling. Agreement between the prediction and experimental results supports the validity of the proposed framework. The framework provides reliable predictions of fatigue crack initiation life for pipelines with girth welds under high-cycle fatigue (HCF) conditions.

This paper presents a full-scale deep-water steel catenary riser fatigue test system. The proposed system can carry out fatigue tests on steel catenary risers, hoses, and subsea pipelines up to 21 m in length, ranging from 8 to 24 inches in diameter. The test system was realized by mechanical loading with loading control systems, and could carry out axial tension and compression, bending moment, torsion, and internal pressure to simulate all load types on deep-water steel catenary risers or subsea pipelines. The counterforce was sustained by a counterforce frame. Through mechanical simulation analysis, the authors determined the size of the counterforce frame and designed the connection form of the counterforce frame and loading system. According to the required loading capacity, the appropriate cylinder thickness and diameter were obtained through calculation. After the design and construction of the test system, the authors designed a fatigue test to confirm the loading capacity and accuracy of the test system. The authors performed full-scale testing to assess the fatigue performance of pipe-to-pipe mainline 5G girth welds fabricated to BS 7608. This test was designed according to the stress level of pipelines in the Lingshui 17-2 gas field, and the test results were compared with the calculation results of the S–N curve.