Crack propagation in near neutral pH (NNpH) environment causes significant threat to pipeline integrity. Internal pressure fluctuations during pipeline operation create variable amplitude loading condition that can propagate corrosion fatigue cracks in NNpH environments. This study is aimed at understanding the effect of load interaction due to mean load pressure fluctuations on crack propagation in pipeline steel under NNpH conditions. The loading condition involved underload followed by an overload at set intervals among minor cycles. The effect of minor cycles, magnitude of overload, and NNpH environment were considered and compared to control test in air. Results showed optimum reduction in crack growth rate at low magnitude of overload in mean load pressure fluctuation. Mini striations observed on fracture surface suggest the contributions of minor cycles to crack propagation due to load interaction. Significant increase in crack growth at high magnitude of overload in NNpH environment indicates the influence of hydrogen.

中文翻译：

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平均载荷压力波动下载荷相互作用和氢对钢管疲劳裂纹扩展行为的影响

裂纹在接近中性pH（NNpH）的环境中传播会严重威胁管道的完整性。管道运行期间的内部压力波动会产生可变的振幅加载条件，该条件会在NNpH环境中传播腐蚀疲劳裂纹。这项研究旨在了解由于平均负载压力波动引起的负载相互作用对管道在NNpH条件下裂纹扩展的影响。加载条件涉及欠载，然后在较小的周期之间以设定的时间间隔过载。考虑了较小循环的影响，过载的大小和NNpH环境，并将其与空气中的对照测试进行了比较。结果表明，在平均负载压力波动较小的过载情况下，裂纹扩展速率的最佳降低。在断裂表面观察到的细小条纹表明，由于载荷相互作用，较小的循环对裂纹扩展的贡献。在NNpH环境中，高过载时裂纹扩展的显着增加表明了氢的影响。