Thermo-mechanical modelling of a single-bead-on-plate weld using the finite element method

In an accompanying paper in this issue a lower bound method based on Melan's theorem was derived and implemented into the Linear Matching Method ratchet analysis procedure. This paper presents a ratchet analysis of a pipe intersection subject to cyclic thermo-mechanical loading using the proposed numerical technique. This work is intended to demonstrate the applicability of the lower bound method to a structure commonly seen in industry and also to better understand the behaviour of this component when subjected to cyclic loading. The pipe intersection considered here has multiple materials with temperature dependent properties. Verification of the results is given via full elastic-plastic analysis in Abaqus.

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Calculation of a lower bound ratchet limit part 2: Application to a pipe intersection and dissimilar material join

In nuclear power plants, ferritic low alloy steel components were connected with austenitic stainless steel piping system through alloy 82/182 butt weld. There have been incidents recently where cracking has been observed in the dissimilar metal weld. Alloy 82/182 is susceptible to primary water stress corrosion cracking. Weld-induced residual stress is main factor for crack growth. Therefore exact estimation of residual stress is important for reliable operating. This paper presents residual stress computation performed by 6” safety & relief nozzle. Based on 2 dimensional and 3 dimensional finite element analyses, effect of welding variables on residual stress variation is estimated for sensitivity analysis. 1. 서 론 최근 V.C Summer 원전 등에서 이종금속용접부 (Dissimilar Metal Weld) 균열이 관찰되었다. (1~3) 균열은 Inconel 계열 용접 금속에서 발생하였으며 일차수응력부식균열(PWSCC)이 균열의 주요 발생 원인이었다. 일차수응력부식균열은 재료의 민감도, 용접부 인장 잔류 응력 및 사용 중 하중(In-service load), 부식 환경과 같은 3가지 인자의 상호작용에 의해 발생한다. (2,4,5)

https://www.koreascience.or.kr:443/article/JAKO200827364506436.pdf

Sensitivity analyses of finite element method for estimating residual stress of dissimilar metal multi-pass weldment in nuclear power plant

In nuclear power plants, ferritic low alloy steel nozzle was connected with austenitic stainless steel piping system through alloy 82/182 butt weld. Accurate estimation of residual stress for weldment is important in the sense that alloy 82/182 is susceptible to stress corrosion cracking. There are many results which predict residual stress distribution for alloy 82/182 weld between nozzle and pipe. However, nozzle and piping system usually connected through safe end which has short length. In this paper, residual stress distribution for pressurizer nozzle of Kori nuclear power plant was predicted using FE analysis, which consideded safe end. As a result, existing residual stress profile was redistributed and residual stress of inner surface was decreased specially. It means that safe end should be considered to reduce conservatism when estimating the piping system. 1. 서 론 최근 들어 V.C Summer, Ringhals 및 Tsuruga 2 등의 원전 이종 금속 용접부(DMW, Dissimilar Metal Weld)에서 (1,2)균열이 발생되었다. 균열의 위치는 상대적으로 운전 압력 및 운전 온도가 높은 원자로(reactor) 및 가압기(pressurizer)의 노즐 용접부로서 균열의 원인은 용접부 금속인 니켈 합금(Alloy 82/182) 재료의 일차수 응력부식균열(PWSCC)로 판명되었다. Alloy 82/182 재료는 응력 부식 균열에 민감하다고 알려져 있으며 주로 이종 금속 용접부 용접 재료로 사용되었다. 응력부식균열은 재료의 민감도, 수화학 환경 및 용접 잔류응력(welding residual stress)의 상호 작용에 의해 발생한다.

http://koreascience.or.kr:80/article/JAKO200824550465170.pdf

Estimation of Residual Stress Distribution for Pressurizer Nozzle of Kori Nuclear Power Plant Considering Safe End

https://research-information.bris.ac.uk/files/124501933/Ring_Weld_Journal_Paper_Part_1_simulations_Rev.0.12_with_Endnote_ref_for_IJSS_ref_as_plain_text.pdf

An optimisation study of the modified deep-hole drilling technique using finite element analyses applied to a stainless steel ring welded circular disc

Welding remains the key process in fabricating, as well as repairing, pressure vessel systems. Unfortunately, many manufacturing and through life service problems occur in or near welded regions. The through life integrity of welded components, e.g. distortion, fatigue, fracture, metallurgy and corrosion control remains a key challenge for structural integrity. The work reported in this paper investigates the complex manufacture and assembly of a pressure vessel toroidal seal. The seal is first created by depositing a series of austenitic welds onto a ferritic pressure vessel to build up a plinth, thus forming a transition weld. The transition weld is then subject to a high temperature Post Weld Heat Treatment (PWHT) to stress relieve the welds and to temper the HAZ in the welds. An austenitic toroidal ring is positioned onto the plinths and welded in place thus forming the toroidal seal. The seal is manufactured from a 347 austenitic stainless steel comprising good ductility and corrosion resistance. The manufacture of the seal is simulated using 2D axisymmetric finite element analysis that are available to support both the design and integrity analysis of welded components. As well as the inherent residual stresses associated with welding, additional effects are important, for instance the austenitic to ferritic transition welds between the vessel body and plinths. This paper presents a novel approach to the simulation of weld metal deposition that is ideally suited to the modelling of transition welds and subsequent PWHT. The plinth welds undergo PWHT and so the creep behaviour of the welds is simulated. A series of intermittent as well as end of manufacture PWHT’s are investigated. Additionally the choice of material hardening law for the austenic weldment is studied. The full manufacturing history of the seal is taken into account within the analysis including welding, component machining and component geometry fit up.Copyright © 2007 by ASME and Rolls-Royce PLC

Modelling the Fabrication of a Pressure Vessel Toroidal Seal

Residual stresses were analysed in a partial penetration weld attaching a tube inside a thick pressure vessel forging, both made of SA508 steel. 2D finite element (FE) analyses methods were used to simulate this multi-pass manual TIG weld. The weld preps are buttered and the forging subsequently heat-treated prior to making the closure weld. Buttering of the forging J-prep and subsequent PWHT creep stress relaxation were modelled. Generally the buttering was found to have minimal influence on the final stress state, although some difference in local peak stress and stress gradients were calculated. Representative test blocks were manufactured, with and without buttered weld preps. Each test block contained two tube penetrations and attachment welds, in order to examine interaction effects. Welding details were captured and peak temperatures recorded by thermocouples were reasonably consistent with the FE model predictions. Surface stresses were measured both in the as-welded condition and after machining, using the hole drilling strain gauge method. Good agreement with FE results was achieved in surface stress levels in the vessel forging, buttering and tube wall. However the 2D model overestimates weld hoop stresses. Large yield magnitude tensile stresses in the vicinity of the joint are balanced by lower compressive stresses in the surrounding PV forging. Interaction effects between the stress fields produced by adjacent tube welds are negligible.Copyright © 2005 by Rolls Royce

Residual Stress Analysis of Tube Attachment Weld in Pressure Vessel Forging: Comparison of FE Predictions and Measurements

This paper presents analyses done to determine residual stress relief achieved by post weld heat treatment (PWHT) of tube attachment welds inside a thick SA508 steel pressure vessel forging. Finite element (FE) analyses were performed modelling the manufacturing operations in detail including welding, machining and PWHT. The analyses demonstrate that PWHT at 600°C for 8 hours is effective in reducing as-welded residual stress levels from tensile yield magnitude (+500MPa approx) to <100MPa. The maximum residual stress was computed to be 90MPa sub-surface in a region of hydrostatic (tri-axial tensile) stress. Secondary creep was modelled using data from creep tests on SA508 steel uni-axial tensile specimens. Practically all of the stress relaxation is due to creep strain with minimal additional plastic strain. Most stress relief occurs during the first hour of soak, with diminishing benefit thereafter. Analysis results also indicate that PWHT effectiveness is more sensitive to soak temperature than hold time. These FE results are considered slightly pessimistic but are reasonably consistent with other analytical predictions. By comparison surface hole drilling stress measurements of <50MPa (10% yield strength) were recorded from a representative welded test block. Analysis pessimism was attributed to ignoring both primary creep and relaxation during the slow warm up phase of the heat treatment cycle.Copyright © 2007 by ASME and Rolls-Royce plc

R. J. Dennis

Papers

Modelling the Fabrication of a Pressure Vessel Toroidal Seal

Residual Stress Analysis of Tube Attachment Weld in Pressure Vessel Forging: Comparison of FE Predictions and Measurements

Residual Stress Relaxation in a Tube Attachment Weld Inside a Pressure Vessel Forging During Post Weld Heat Treatment