Material and residual stress considerations associated with the autofrettage of weld clad components

G Benghalia,J Wood

doi:10.1016/j.ijpvp.2016.02.003

G Benghalia, J Wood

Open Access

https://doi.org/10.1016/j.ijpvp.2016.02.003

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Abstract

A fatigue-resistant cladding concept confirms the presence of compressive residual stresses in a cylinder weld clad with 17–4 PH stainless steel while tensile residual stresses exist in an Inconel 625 clad layer. In this study, autofrettage of an Inconel 625 thick-walled clad cylinder is investigated with modified residual stress distributions obtained indicating that tensile residual stresses throughout the clad layer are transformed to compressive in nature, discontinuity stresses at the clad/substrate interface are almost entirely eliminated and compressive residual stresses exist to a depth of around 18 mm. An alternative clad material, 17–4 PH stainless steel, is investigated resulting in compressive residual stresses in the clad layer without the need for autofrettage. The complexity of modelling a martensitic stainless steel is discussed and sensitivity studies undertaken to illustrate the influence of coefficient of thermal expansion on resulting residual stresses. Strain hardening effects and the assumption of an idealised interface are discussed. Contour method measurements prove that discontinuity stresses are reduced in reality due to alloying and diffusion effects, highlighting also the need for further characterisation of 17–4 PH. Additional considerations such as the weld clad profile and process parameters are briefly discussed.

Highlights

The issue of fatigue failure in weld clad components, such as pipelines utilised in the oil and gas industry, has prompted an investigation into a fatigue-resistant cladding technology to enhance the performance of these components
Examining the hoop stress distribution, it is observed that the initial damaging tensile residual stress throughout the clad layer has been transformed to beneficial high compressive levels at both autofrettage pressures
Applying a high autofrettage pressure of 800 MPa produces high compressive residual stresses in the clad layer and into the substrate alongside a compressive discontinuity stress at the interface. This compressive discontinuity stress may be desirable depending on the metallurgy of the joint and the resulting mechanical properties achieved for the dissimilar materials at the joint

Summary

Introduction

The issue of fatigue failure in weld clad components, such as pipelines utilised in the oil and gas industry, has prompted an investigation into a fatigue-resistant cladding technology to enhance the performance of these components. Fatigue of welded joints and dissimilar material joints have been studied with focus placed on weld cladding of 4330 low alloy carbon steel. Two clad materials are investigated, namely nickel-chromium-based superalloy Inconel 625 and 17e4 PH stainless steel. The application of a coating or cladding to a substrate using a thermal deposition process results in a self-equilibrating residual stress distribution primarily due to the thermal cycle and the associated metallurgical changes during the melting, deposition, solidification and cooling of the material. The arising constraint on differential expansion and associated phase changes results in residual stresses, with material property variation with time and temperature influencing the residual stress state. Dissimilarity in properties between substrate and clad materials further affects the self-equilibrating residual stress field. Due to the interest in fatigue performance, the arising residual stress state post-cladding is evaluated

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