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

Paper Number: 122092

122092 - Allowable Circumferential Flaw Sizes Based on Code Given and Actual Measured Flow Stresses for High Toughness Ductile Pipes Subjected to Bending and Tensile Loads 

Allowable stresses for pipes are determined by the combination of failure stresses and safety factors. When predicting the plastic collapse failure stresses for high toughness ductile pipes, flow stresses of the pipe materials are indispensable. The flow stress is normally given by the average of the yield stress and the ultimate tensile strength of the pipe material. The American Society of Mechanical Engineers (ASME) Code Section XI Inservice Inspection states to use the yield stresses and the ultimate tensile strengths defined by the ASME Code Section II Materials. The ASME Code Section XI also states that actual measured yield stresses and ultimate tensile strengths are possible to be used, alternatively. The yield stress and ultimate tensile strength given by the ASME Code Section II are conservative compared to actual measured values, as expected. Then, it is easily understandable that the allowable stresses calculated by the code given flow stress are lower than the allowable stresses calculated by the actual measured flow stress. The objective of this paper is to compare the plastic collapse and allowable stresses based on both the code and actual flow stresses for pipes with circumferential flaws subjected to bending and tensile loading. In addition, it is demonstrated that allowable flaw sizes based on both the code and actual flow stresses do not differ much at low allowable stress. However, when the allowable stress is large, the allowable flaw size based on the code flow stress is significantly lower compared to that based on the actual flow stress.

Presenting Author: Martin Negyesi Centre for Advanced and Innovative Technologies – VŠB-Technical University of Ostrava

Presenting Author Biography: University studies finished in 2014, awarded by PhD title. During studies 6 months traineeship in Joint Research Center in Petten (Netherlands). Working as junior researcher in UJP Praha a.s. (Czechia) till 2015 and 5 years in Japan Atomic Energy Agency (Japan) till 2020. The main research topic was nuclear fuel safety. From 2020 researcher in Centre for Advanced and Innovative Technologies at VSB-TUO (Ostrava, Czechia). The main research topic is structural integrity assessment.

Authors:

Martin Negyesi Centre for Advanced and Innovative Technologies – VŠB-Technical University of Ostrava
Yoosung Ha Japan Atomic Energy Agency
Kunio Hasegawa Japan Atomic Energy Agency
Valery Lacroix Tractebel Engineering