Structural Integrity Assessment of Welded Pipeline Designed with Reduced Safety

Abstract

The main goal of this paper was to assess the integrity of welded joints in the main pipeline of the reversible hydropower plant "Bajina Bata". Japanese steel Sumiten 80P (SM 80P) was used as the parent material. European recommendation for pipeline safety factor is equal to 1.7 and this value was used for calculations of the RHPP "Bajina Bata", whereas the value recommended by Japanese standards is 2.1. A relatively small safety factor, which is different from the Japanese recommendation (since the material itself is Japanese), represented one of the main reasons for a detailed investigation of the pipeline structural integrity and safety, using the prototype. In the case of pressure vessels, the welded joint is a location of stress concentration, which can act in the same way as residual stresses. Assessment of prototype test results is possible to perform based on stress and strain calculations of vessels with ideal geometry. For this reason, the solution for thin-walled vessels is given, both in elastic and elastic-plastic areas. Numerous tests were performed in order to obtain a reliability assessment necessary for the construction of the pipeline, since the consequences of potential failure would be disastrous in this case. A numerical simulation, based on the experimentally determined mechanical properties of the material used, was also performed in order to obtain the stress/strain distribution. These results were then compared to the experimentally obtained ones, and it was concluded that there is a good level of compliance between numerical and experimental results.