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research-article

Stress Intensity Factors for Transformed Surface Flaws and Remaining Fatigue Lives Based on Flaw-to-Surface Proximity Rules

[+] Author and Article Information
Kunio Hasegawa

Consultant, Center of Advanced Innovation Technologies, VSB-Technical University of Ostrava, 17. Listopadu 15/2172, 708 33, Ostrava-Poruba, Czech
kunioh@kzh.biglobe.ne.jp

Bohumir Strnadel

Center of Advanced Innovation Technologies, VSB-Technical University of Ostrava, 17. Listopadu 15/2172, 708 33, Ostrava-Poruba, Czech
Bohumir.strnadel@vsb.cz

Yinsheng Li

Japan Atomic Energy Agency (JAEA), Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195, Japan
li.yinsheng@jaea.go.jp

Valery Lacroix

Tractebel (ENGIE), Bd. Simon Bolivar 34-36, B-1000 Brussels, Belgium
valery.lacroix@tractebel.engie.com

1Corresponding author.

ASME doi:10.1115/1.4040640 History: Received January 16, 2018; Revised June 13, 2018

Abstract

Subsurface flaws are sometimes found as blowholes near free surfaces of structural components. Net-section stress at the ligament between the free component surface and the subsurface flaw increases when the ligament distance is short. It can be easily expected that the stress intensity factor at the tip of the subsurface flaw increases with decreasing the ligament distance. Fitness-for-service (FFS) codes provide flaw-to-surface proximity rules which are transformation from subsurface to surface flaw. Although the concept of the proximity rules of the FFS codes are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws are significantly different amongst FFS codes. This study demonstrates the proximity criteria provided by the FFS codes and indicates that the increment of the stress intensity factors before and after the transformation depends on the flaw aspect ratio and the location at the transformation from subsurface to surface flaws. In addition, it is shown that remaining fatigue lives for pipes with flaws are strongly affected by the location at the transformation from subsurface to surface flaws.

Copyright (c) 2018 by ASME
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