A study of double and multiple loading of rod-type test samples made of pipe steel

During transmission pipelines pressure testing, the value of the test pressure is taken to be equal to 1.1 of the working pressure for sections of the normal category and 1.25 or 1.5 for sections of higher categories. The substantiations of the above values date back to the middle of the 20-th century, and may need to be reconsidered in the light of the new-generation pipe materials implementation. This paper aims to identify the optimal safety factor for pressure testing of main pipelines, taking into account the material of the pipes, as well as the variation of the destructive power in case of multiple loading of the test objects. The findings will allow confirming or revising the existing approach to assigning the strength test pressure of main pipelines and theoretically substantiating the observed phenomena. In practice, that will allow establishing the optimal parameters for testing gas pipelines, ensuring the required dependability and safety. The research is relevant due to the continuous improvement of pipe steels, as well as in the light of innovative pipe material development. An analysis of foreign and Russian experimental studies involving double loading of steel test objects to failure indicates that – before the second loading – the destructive force can be reduced to 90% of the first loading value. The available statistical sample of foreign and Russian experiments is small, while the methodology is complex. Given the above, the authors developed an original methodology, that was used in destructive double loading experiments on steel test objects and statistical analysis of the results.

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