Internal pressure fatigue of pipes, pipelines and cylinders

In pipelines and cylinders, pipes are exposed to both static and fatigue loads. In this context, especially internal pressure fatigue is of importance. Because of the incompressibility of liquid media, significant internal pressure fluctuations have to be taken into account when designing oil and water pipeline systems. While during regular service of high pressure gas transmission lines major fluctuations are not expected, internal pressure fatigue may occur in storage systems like natural gas storage arrays constructed large diameter pipes. Such storage systems are used by local gas distributors in order to compensate for consumption peaks. For the future it is anticipated that also larger sections of gas transmission lines will be used for storage reasons and thereby will be exposed to internal pressure fatigue. Fatigue loads have to be evaluated on the basis of lifetime assessments. Another future application of gas storage systems is the transportation of natural gas by ship using the compressed / pressurized natural gas technology (CNG / PNG®). In this technology, large diameter UOE pipes are used to construct pressure vessels on ships. The cylinders are exposed to pressure cycles between 25 and 250 bars and, thus, require specific fatigue design. In the present paper, design conditions for pipes, pipelines and cylinders subjected to internal pressure fatigue will be discussed. National and international standards will be compared to results of internal pressure fatigue tests. Applications and their safety concepts will be introduced. (AU)