Study of Residual Stresses and Microstructural Changes in Charpy Test Specimens Reconstituted by Various Welding Techniques

Gizo Bokuchava,Peter Petrov

doi:10.3390/met10050632

Abstract

Changes in the reactor pressure vessel (RPV) material properties due to neutron irradiation are monitored by means of surveillance specimen programs, which are used for realistic evaluation of the RPVs’ lifetime. Due to a limited number of surveillance specimens, the evaluation of reconstitution methods by various welding techniques after Charpy impact tests is of great importance. Time-of-flight (TOF) neutron diffraction method was used to determine the residual stress distributions and microstructural changes in Charpy specimens welded by arc stud, electron, and laser beam welding techniques. The lowest level of the residual stress in weld seams regions was found for the specimen welded by electron beam with optimal parameters as compared to other techniques. At the same time, this specimen exhibits the maximal level of microstrain, which points to high dislocation density in the material. The corresponding contributions to the yield strength due to various strengthening mechanisms were estimated.

Highlights

The control of the reactor pressure vessel (RPV) metal condition during its lifetime and guarantee of the reactor vessel integrity under normal operating conditions, as well as during any design accidents is one of the vital problems of modern nuclear power engineering
The RPVs are exposed to intense neutron irradiation, which results in reactor vessel steel deterioration and severe changes in its physical and mechanical properties manifested mainly as increased brittleness
The electron beam welding (EBW) specimens demonstrate the residual stress level varying from −85 MPa to 172 MPa for

Summary

Introduction

The control of the reactor pressure vessel (RPV) metal condition during its lifetime and guarantee of the reactor vessel integrity under normal operating conditions, as well as during any design accidents is one of the vital problems of modern nuclear power engineering. The RPVs are exposed to intense neutron irradiation, which results in reactor vessel steel deterioration and severe changes in its physical and mechanical properties manifested mainly as increased brittleness. For this reason, special monitoring programs are used to control the RPV metal condition by means of surveillance specimens, which are located near reactor vessel and are made of the same material. Surveillance specimens program based on results of their mechanical tests provides verification of the project design characteristics of brittle fracture resistance, evaluation of the RPV functionality, and the material testing maintenance of its operation over the whole project period

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