Weld Residual Stress Profiles Research Articles

Probabilistic kernel machines for predictive monitoring of weld residual stress in energy systems

Predictive monitoring supports the a priori scheduling of critical component maintenance and contributes significantly in attaining a safe yet economic operation and management of complex energy systems by mitigating the risk of accidents and minimizing the number of operational pauses. The current work studies the learning ability of probabilistic kernel machines, and more particularly of Gaussian Processes (GP) equipped with various kernels for the estimation of weld residual stress profiles of stainless steel pipe welds. The GP models are tested on experimentally-obtained data of axial and hoop residual stresses in two different stainless-steel pipes. The results exhibit the ability of GP to accurately predict the weld residual stress profile in the axial and hoop direction by providing a predictive distribution, i.e., mean and variance values. Furthermore, performance of GP is compared to a non-probabilistic kernel machine, such as support vector regression (SVR) equipped with the same kernels, and to multivariate linear regression (MLR). Comparison results exhibit the robustness of GP over SVR and MLR with respect to prediction accuracy of weld residual stress in terms of root mean square error. With respect to a second metric, namely, correlation coefficient between measured and predicted values, GP is superior to SVR and MLR in the majority of the cases.

Through-Thickness Residual Stress Profiles in Austenitic Stainless Steel Welds: A Combined Experimental and Prediction Study

Economic and safe management of nuclear plant components relies on accurate prediction of welding-induced residual stresses. In this study, the distribution of residual stress through the thickness of austenitic stainless steel welds has been measured using neutron diffraction and the contour method. The measured data are used to validate residual stress profiles predicted by an artificial neural network approach (ANN) as a function of welding heat input and geometry. Maximum tensile stresses with magnitude close to the yield strength of the material were observed near the weld cap in both axial and hoop direction of the welds. Significant scatter of more than 200 MPa was found within the residual stress measurements at the weld center line and are associated with the geometry and welding conditions of individual weld passes. The ANN prediction is developed in an attempt to effectively quantify this phenomenon of ‘innate scatter’ and to learn the non-linear patterns in the weld residual stress profiles. Furthermore, the efficacy of the ANN method for defining through-thickness residual stress profiles in welds for application in structural integrity assessments is evaluated.

Numerical investigation of formation mechanism of welding residual stress in P92 steel multi-pass joints

Three plate joints, namely, single-pass weld, double-pass weld, and four-pass weld were fabricated using P92 steel. The hole-drilling strain-gauge method and X-ray diffraction technique were employed to measure the welding residual stresses. Optical microscope and Vickers hardness tester were used to characterize the micro-structure and hardness of these joints, respectively. A thermal-metallurgical-mechanical finite element method (FEM) based on SYSWELD software was developed to simulate welding residual stress in P92 steel joints. Using the developed computational approach, the welding residual stress profiles in single-pass, double-pass and four-pass welded joints were calculated. The effectiveness of the developed computational approach was verified by the experimental measurements. The longitudinal stress vs. temperature evolution in double-pass welded joint was also examined. Numerical experiments of Satoh test were performed to study the influence of solid-state phase transformation, peak temperature and re-heating on the evolution of residual stresses. The solid-state phase transformation has a significant influence on the formation of welding residual stress, and the peak temperature of final thermal cycle can determine the magnitude of final residual stress.

Residual Stress, Microstructure and Hardness of Thin-Walled Low-Carbon Steel Pipes Welded Manually

The aim of this work is to evaluate the welding residual stress profile in ASTM A106 Gr. B steel pipes with 4 diameter and to correlate this profile with the microstructure and hardness of the joint. The results showed that the residual stresses are more uniform for a lower welding heat input. Higher welding heat input causes not only a non-uniformity of the stress profile but also promotes the maximum stress as high as the yield strength. The microstructure was composed of ferrite, perlite and possibly bainite; the presence of martensite was not verified. The hardness results indicated that none of the welding parameters used produced levels of hardness greater than 249 HV. Such a result is of fundamental importance because it suggests that low hardness does not necessarily mean low residual stress levels.

Simplified Weight Function for Calculating Stress Intensity Factor in Complicated Stress Distributions

Calculation of a stress intensity factor becomes more difficult when crack are subjected to a complicated stress distribution profile. A standard procedure called influence coefficients is inadequate, because a stress profile may not be accurately represented by a polynomial function. This paper applies a piecewise linear approximation of stress profile and a weight function method to overcome that restriction. However, the typical adopted weight function, i.e. universal weight function, is replaced by a weight function, in which its form coincides with the analytical form. Although a new weight function consists of lesser number of terms, it is proved to be accurate when applies to a cracked-cylinder problem, e.g. internal part-through circumferential crack and internal fully circumferential crack under various complicated weld residual stress profiles. Using this simpler weight function and linearized approximation scheme led to a closed-form stress intensity factor solution, which is convenient for programming.

Effect of Weld Residual Stress Fitting on Stress Intensity Factor for Circumferential Surface Cracks in Pipe

Recent studies have shown that the crack growth of primary water stress corrosion cracking (PWSCC) is mainly driven by the weld residual stress (WRS) within the dissimilar metal weld. The existing stress intensity factor (K) solutions for surface cracks in pipe typically require a fourth order polynomial stress distribution through the pipe wall thickness. However, it is not always possible to accurately represent the through thickness WRS with a fourth order polynomial fit and it is necessary to investigate the effect of the WRS fitting on the calculated Ks. In this paper, two different methods were used to calculate the K for a semi-elliptical circumferential surface crack in a pipe under a given set of simulated WRS. The first method is the universal weight function method (UWFM) where the through thickness WRS distribution is represented as a piece-wise monotonic cubic fit. In the second method, the through thickness WRS profiles are represented as a fourth order polynomial curve fit (both using the entire wall thickness data and only using data up to the crack-tip). In addition, three-dimensional finite element (FE) analyses (using the simulated weld residual stress) were conducted to provide a reference solution. The results of this study demonstrate the potential sensitivity of Ks to fourth order polynomial fitting artifacts. The piece-wise WRS representations used in the UWFM were not sensitive to these fitting artifacts and the UWFM solutions were in good agreement with the FE results. In addition, in certain cases, it was demonstrated that more accurate crack growth calculations of PWSCC are made when the UWFM is used.

Prediction of Welding Residual Stress Profile in Dissimilar Metal Nozzle Butt Weld of Nuclear Power Plant

This paper provides the through-thickness welding residual stress profile in dissimilar metal nozzle butt welds of pressurized water reactors. There have been incidents recently where cracking has been observed in the dissimilar metal weld. Weld-induced residual stress is main factor for crack growth, and thus, exact estimation of welding residual stress is important. For investigations of welding residual stress profile, the effects of geometric variables, i.e. the thickness and the radius of the nozzle and the length of the safe end, on welding residual stresses, are systematically considered and elastic-plastic thermo-mechanical finite element analyses are conducted. Through-wall welding residual stress profiles for dissimilar metal nozzle butt welds are proposed, which take a modified form of existing welding residual stress profiles developed for austenitic pipe butt weld in R6 code.

Assessment of residual stress of welded structural steel plates with or without post weld rolling using the contour method and neutron diffraction

The post-welding rolling technique was used to modify the welding residual stress profile of butt joints of S355 structural steel. Two different residual stress measurement techniques were used: contour method and neutron diffraction. A good agreement between the results of both measurement techniques was found, illustrating the capability of the contour method to provide data otherwise available only using costly neutron and synchrotron radiation. The effect of post-weld roller tensioning on residual stress consisted in a substantial change in residual stress profile, with the large tensile stresses along the weld seam becoming compressive

Evaluation of stress intensity factors due to welding residual stresses for circumferential cracked pipes

To investigate the applicability of existing methods to estimate stress intensity factors due to welding residual stresses, comparisons with finite element (FE) solutions are made for two types of generic welding residual stress profiles, generated by simulating repair welds. It is found that fitting residual stresses over the crack depth using third-order polynomials gives good estimates of stress intensity factors but fitting over the entire thickness can result in inaccurate estimates even with fourth-order polynomials. Noting that welding residual stresses are often determined from FE analyses, linearization of residual stresses to estimate stress intensity factors is proposed. Comparison with FE solutions shows good agreements.

가압경수로 노즐 맞대기 이종금속용접부의 용접잔류응력 예측

가압경수로의 많은 관통관 중에서 니켈 기저 합금인 Inconel alloy 600 계열의 이종금속용접부는 일차수응력부식균열에 민감하며, 이를 평가하기 위하여 용접부에 작용하는 잔류응력분포를 정확히 예측하는 것이 중요하다. 본 논문에서는 유한요소해석을 이용하여 노즐 맞대기 이종금속용접부에 작용하는 일반적인 잔류응력분포를 예측하였다. 이를 위해 노즐 맞대기 이종금속용접부의 형상을 단순화하여 특정한 형상변수에 따른 용접부 잔류응력분포를 확인하였으며, 이를 토대로 기존 문헌에 제시된 오스테나이트계 배관맞대기 용접부 잔류응력 분포식을 수정하여 가압경수로 노즐 맞대기 이종금속용접부에 작용하는 일반적인잔류응력분포 예측식을 제시하였다.

704 相変態を伴う低合金鋼の溶接における先行パスの残留応力に及ぼす後続パスの入熱の影響(OS10-1 オーガナイズドセッション《発電機器の材料・構造解析と評価》)

We developed a residual stress analysis method for bead welded low alloy steel plates by considering phase transformation strain. Phase transformation usually occurs during the welding process in a low alloy steel and affects on welding residual stress profiles. The amount of phase transformation strain was taken into account in the analysis method. First, the method was applied to predict welding residual stress profiles in a specimen, which was bead welded on both sides of a low alloy steel plate. The analysis results showed that the longitudinal stress at the center of the weld was 250 MPa on the first pass welded side after the first weld was completed. The longitudinal stress increases to 320 MPa after the second weld was completed. Then, residual stress of the specimen was measured to validate the analysis results. The analysis results agree well with the measurement results. These findings suggest that a subsequent weld pass heat input affects on residual stress profile generated by the previous weld pass heat input.

Through-wall welding residual stress profiles for dissimilar metal nozzle butt welds in pressurized water reactors

This paper provides approximate expressions for through-wall welding residual stresses in dissimilar metal nozzle butt welds of pressurized water reactors. An idealized shape of nozzle is proposed, based on which systematic elastic-plastic thermo-mechanical finite element analyses are conducted by varying the thickness and radius of the nozzle and the length of the safe-end. Based on the results, a through-wall welding residual stress profile for dissimilar metal nozzle butt welds is proposed by modifying the existing welding residual stress profile for austenitic pipe butt welds in the R6 procedure.

유한요소법을 이용한 박판 맞대기 용접부 잔류응력 및 균열 해석

본 논문은 박판 맞대기 용접부 잔류응력을 3 차원 유한 요소법을 이용해서 모사하였다. 경계조건이 잔류응력에 미치는 영향을 연구하기 위해 다양한 경계조건이 고려되었으며, 예측된 용접 잔류응력은 기존 문헌의 내용과 비교 검증하였으며, 본 연구의 결과는 박판 용접부 균열에 발생하는 잔류응력의 영향을 해석하는데 사용될 것이다. In this study, we calculate the welding residual stresses for a butt-welded thin-walled plate by carrying out threedimensional finite-element analyses. To study the effect of mechanical boundary conditions on the welding residual stresses, various boundary conditions are considered. The welding residual stresses obtained in the measurements and finite-element analyses are validated by comparing them with the welding residual stress profiles in the R6 code. The results of this study are used to analyze the influence of residual stress on the crack formation in thin-section weldments.

Treatment of residual stress in failure assessment procedure

The effect of residual stress on component failure has been investigated using the distributions from current failure assessment procedures, and a residual stress profile simple to apply with less conservatism has been proposed for the weld geometries of T-plate and tubular T-joint. The stress intensity factors (SIFs) in the two weld geometries under various types of loads have been calculated using the Green’s function method. The Green’s functions were determined not only for the T-plate but also for the tubular T-joint with the built-in ends. The use of a linear (bending) stress profile, derived from an analysis of measured residual stress distributions in T-plate and tubular T-joints, has been examined. The profile was validated with experimentally measured residual stress distributions in two materials, a high strength and medium strength ferritic steel and two geometries, a T-plate joint and a tubular T-joint for crack lengths up to half the plate or pipe thickness. Whereas the recommended residual stress distributions are geometry and material specific, it is shown that a simplified linear bending profile provides a possible guideline, applicable to a range of materials and geometries, where detailed information on weld procedures or residual stress profiles are unavailable.