Verification of the Combination Rules of Multiple Flaws in ASME B&PV Code Section XI: A Case Study of Two Adjacent Surface Planar Flaws

In nuclear pressure vessels, multiple surface cracks are often found by regular inspection. In order to evaluate the integrity of the vessels, ASME B&PV Code Section XI provides the flaw combination rules; however, its accuracy has not been clarified yet. For the analyses of interacting multiple semi-elliptical surface cracks, in 1983 Nishioka and Atluri developed the Vijayakumar, Nishioka, and Atluri (VNA) solution-finite element alternating method which is highly accurate and cost effective. Using this highly accurate VNA-finite element alternating method, the case of extremely closely located two interacting coplanar cracks was analyzed. From the numerical results, it is found that the B&PV Code Section XI provides a conservative flaw combination rule. Therefore, the B&PV Code Section XI is precisely verified by modern and accurate computational technologies.