Influence of welding stresses on relief cracking during heat treatment of a creep-resistant 13CrMoV steel Part III: assessment of residual stresses from small-scale to real component welds

D Schroepfer,T Kannengiesser,A Kromm,M Rhode,R C Wimpory,T Lausch

doi:10.1007/s40194-021-01101-7

Abstract

For higher operational temperatures and pressures required in petrochemical plants, the modified 13CrMoV9-10 steel was developed providing high resistance against creep and compressed hydrogen. Extreme care during the welding procedure is necessary for this steel, attributed to low toughness, high strength in as-welded state, and increased susceptibility to stress relief cracking (SRC) during post-weld heat treatment (PWHT). Previous research of SRC in creep-resistant steels discussed mainly thermal and metallurgical factors. Few previous findings addressed the influences of welding procedure on crack formation during PWHT considering real-life manufacturing conditions. These investigations focus on effects of welding heat control on stresses during welding and subsequent PWHT operations close to realistic restraint and heat dissipation conditions using a special 3D testing facility, which was presented in parts I and II of this contribution. Part III addresses investigations on residual stress evolution affecting crack formation and discusses the transferability of results from large-scale testing to laboratory-scale. Experiments with test set-ups at different scales under diverse rigidity conditions and an assessment of the residual stresses of the weld-specimens using X-ray (surface near) and neutron diffraction analysis (bulk) were performed. This study aims to provide a way of investigating the SRC behaviour considering component-specific residual stresses via small-scale testing concepts instead of expensive weld mock-ups.

Highlights

Efficiency and flexibility are currently a major concern in the design of modern power plants and chemical processing facilities
The aim is to increase the toughness of the weld joints as well as to reduce the welding induced residual stresses
According to commonly established models and concepts, e.g. by the authors of [21, 22], a saturation is reached at a weld seam length of approx. 400 mm, so that from this length a kind of maximum of the restraint level in the longitudinal direction of the seam and of the expected welding stresses is achieved

Summary

Introduction

Efficiency and flexibility are currently a major concern in the design of modern power plants and chemical processing facilities. Due to the large dimensions and wall thickness of the reactors (wall thickness up to 475 mm) and the special alloy concept, reliable weld manufacturing of the components is extremely challenging [1]. Low toughness and high strength of the weld joint in the as-welded condition are critical regarding weld cracking. High welding residual stresses are the result of the highly restrained shrinkage of the component welds. For this purpose, the entire component must be subjected to postweld heat treatment (PWHT) after completion of the welding operation [2]. The aim is to increase the toughness of the weld joints as well as to reduce the welding induced residual stresses. V-modified CrMo steels possess an increased susceptibility to cracking during stress relaxation, so-called stress relief cracking (SRC) [3]

Objectives

Results

Conclusion