When flaws are detected in pressure retaining components, assessments have to be done in order to demonstrate the fitness-for-service (FFS) of the component for continued operation. This FFS demonstration is performed in accordance with FFS Codes providing by flaw assessment procedures and acceptance standards. Before performing analyses, a flaw characterization has to be carried out in order to determine unequivocally the flaw geometry. This flaw characterization is done according to rules provided in the FFS Codes and hence appears as crucial for the rest of the flaw assessment.

The first step of the flaw characterization addresses the interaction of the flaw and the free surface of the component: if a subsurface flaw is located near the free surface, this step consists of characterizing the flaw as surface or subsurface according to subsurface-to-surface flaw proximity rules. The re-characterization process from subsurface to surface flaw is addressed in all fitness-for-service (FFS) Codes. The second step of the flaw characterization addresses the interaction of the flaw with adjacent flaws: if a flaw is located near another flaw, this step consists of combining the flaws between them according to flaw proximity rules.

However, in some FFS Codes and in the ASME B&PV Section XI Code particularly, there is a lack on how to treat the interaction of a combined flaw and  the free surface of the component. The ASME B&PV Section XI Code flaw characterization is not clear on this topic which could lead to misinterpretations and unreliable flaw assessment results.

Some typical examples of unrealistic flaw assessment results due to these misinterpretations of ASME Section XI flaw characterization rules are depicted in this paper. After analyzing more in-depth the origin of the inconsistencies based on 3D XFEM calculations, the paper is used as Technical Basis for the improvement of the ASME Section XI Code in order to clarify the treatment of combined flaw in the flaw characterization (IWA-3300) and in the flaw acceptability assessment as well (IWB/IWC-3510).


Treatment of the Interaction With the Free Surface of the Component for Combined Subsurface Flaws \u2013 Technical Basis for Revision of Iwa-3300 and Table Iwb/iwc-3510-1

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

PVP2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.