Session: CS-23-01 Improvement of Flaw Assessment Procedures in Fitness-for-Service Codes

Paper Number: 122902

122902 - Proposal of a New Flaw-to-Surface Proximity Rule for the Re-Characterization of a Subsurface Flaw Into a Surface Flaw 

When a subsurface flaw is detected close to the free surface of a pressure retaining component, it must be assessed whether the subsurface flaw shall be transformed into a surface flaw in accordance with flaw-to-surface proximity rules. Those re-characterization rules assume implicitly that if the interaction between the subsurface flaw and the free surface is too high, the remaining ligament is susceptible to break leading to this re-characterization of the subsurface flaw into a surface flaw. This re-characterization process from subsurface to surface flaw is adopted in all Fitness for Service (FFS) Codes. In the Section XI of ASME Boiler & Pressure Vessel Code, the limit value for this proximity rule depends on ratio between the subsurface flaw to the free surface distance (i.e., the remaining ligament) and on the flaw depth. This limit value does not depend on the flaw aspect ratio.

This paper firstly demonstrates that, in reality, for a given flaw depth, the interaction between the subsurface flaw and the free surface of the component depends highly on the flaw aspect ratio. Therefore, the current flaw-to-surface proximity rule should account for this parameter as well. Then, the paper proposes an interaction limit criterion and presents a new limit value for the flaw-to-surface proximity factor, depending on the flaw depth, the remaining ligament and the flaw aspect ratio as well.

Presenting Author: Valery Lacroix Tractebel Engie

Presenting Author Biography: Dr. Valery Lacroix is Chief Engineer at Tractebel (ENGIE) and Global Expert for ENGIE group.
He received his PhD in Mechanical Engineering from the Yokohama National University.
He has more than 20 years of experience in Fracture Mechanics and 15 years of experience in Nuclear Industry.
He is member of several ASME Working Groups and is currently Chair of Codes & Standards Track for PVP Conference.

Authors:

Valery Lacroix Tractebel Engie
Pierre Dulieu Tractebel Engie
Kunio Hasegawa Japan Atomic Energy Agency