Low Cycle Fatigue Behavior of Elbows with Local Wall Thinning

Muhammad Faiz Harun,Roslina Mohammad,Andrei Kotousov

doi:10.3390/met10020260

Abstract

There have been a number of studies concerning the integrity of high-strength carbon steel pipe elbows weakened by local pipe wall thinning, the latter can be typically caused by flow accelerated erosion/corrosion. In particular, the focus of several recent studies was on low cycle fatigue behavior of damaged elbows, mainly, in relation to strength and integrity of piping systems of nuclear power plants subjected to extreme loading conditions, such as earthquake or shutdown. The current paper largely adopts the existing methodology, which was previously developed, and extends it to copper-nickel elbows, which are widely utilized in civil infrastructure in seismically active regions. FE (finite element) studies along with a full-scale testing program were conducted and the outcomes are summarized in this article. The overall conclusion is that the tested elbows with various severity of local wall thinning, which were artificially introduced at different locations, demonstrate a strong resistance against low cycle fatigue loading. In addition, elbows with wall thinning defects possess a significant safety margin against seismic loading. These research outcomes will contribute to the development of strength evaluation procedures and will help to develop more effective maintenance procedures for piping equipment utilized in civil infrastructure.

Highlights

Elbows are common components in piping systems, primarily used to change the direction of flow and, are frequently subjected to flow-induced corrosion and erosion
Some general conclusions from the experimental results can be summarized as follows: (1) Local wall thinning at extrados and intrados regions does not significantly affect low cycle fatigue
(1) Local wall thinning at extrados and intrados regions does not significantly affect low cycle life of damaged elbows

Summary

Introduction

Elbows are common components in piping systems, primarily used to change the direction of flow and, are frequently subjected to flow-induced corrosion and erosion. There were several recent studies both experimental and numerical addressing the problem of structural integrity and life of carbon steel elbows under severe loading conditions [6,7,8,9,10,11,12,13,14,15,16]. The difficulties in prediction methodologies are largely attributed to numerous factors, which influence the strength and integrity of elbows with wall thinning defects [7] Some of these factors are currently disregarded in design and evaluation procedures or incorporated through the use of large safety factors [6,7,8]. This paper summarizes main outcomes of the experimental program and numerical studies with a focus on the influence of the dimensions and location of thinning defects on low cycle fatigue life. These additional results will be presented and discussed in other publications

Material and Specimens

Testing Apparatus

Low Cycle Behavior of Sound Elbows

Low Cycle Behavior of Elbows with Local Wall Thinning

Safety Margin Evaluation

Conclusions