The STYLE EU Framework 7 project is examining the structural integrity of non-RPV components in reactor primary circuits. One of its focus areas is the impact of high magnitude weld residual stresses on the initiation and growth of cracks in austenitic stainless steels. A large scale fracture test has been performed on Mock-up 2, a butt-welded austenitic steel pipe containing a short, deep weld repair that induces weld residual stresses of yield magnitude over the length of repair. A through-thickness crack was introduced into the repair weld, and its behaviour under superimposed global bending load was investigated in a large scale fracture test. This paper describes the process of test design, the pre-test predictions made using the R6 defect assessment procedure, and the outcome of the test.

A number of girth-welded pipe mock-ups have been manufactured and investigated during the STYLE project, using a wide range of measurement techniques accompanied by extensive finite element simulation campaigns. This paper gives an overview of the work carried out and presents preliminary conclusions on the performance of finite element weld residual stress simulation techniques in the different mock-up designs.

As part of the STYLE EU FP7 project a modified 1:5 scale replica of a VVER-440 type reactor pressure vessel inlet nozzle was manufactured. The nozzle included a dissimilar metal weld of the type found in full-scale nozzles. This scale model was developed to permit accurate measurements to be made and detailed finite element (FE) models to be developed without recourse to using a full scale mock-up. It was also found that a full-scale mock-up would not permit the application of certain residual stress measurement methods. Temperatures and displacements were recorded during welding of the dissimilar metals, with measurements used to guide simulation of the welding process using finite element models. Through thickness residual stress profiles were measured using a comprehensive range of different techniques, such as deep hole drilling, neutron diffraction, magnetic Barkhausen noise. Usage of contour method had been planned too, but it but could not be accomplished in due time. The measured residual stresses obtained by the different methods are presented and compared. Measured residual stresses, temperatures and displacements were then used to validate the results derived from the FE model.

The presence of welding residual stresses is known to influence fracture of welded metallic structures. Where there is significant ductile deformation prior to fracture, welding residual stresses are often perceived to be removed as plasticity is accumulated and do not subsequently contribute to fracture. To explore this, a large scale experiment was conducted as part of the EU-STYLE project. One experiment was performed on a repair welded stainless steel pipe subjected to four-point bending. There was evidence of limited ductile tearing prior to collapse of the pipe. Prior to testing, residual stress measurements were made through the repair weld and opposite the repair weld in the original girth weld of the pipe. These measurements were used as input to a finite element (FE) model. An iterative technique was employed to map measured residual stresses onto an uncracked FE model, and an equilibrium state determined. The residual stress state was then mapped onto a cracked pipe FE model which was then used to simulate the pipe's behaviour. The simulations reveal that the presence of tensile residual stresses contributes significantly to initial yielding behaviour but as plasticity progresses the residual stresses are removed.

Through thickness measurement of residual stresses is now undertaken routinely for complex welded components. To predict residual stress distributions finite element (FE) simulations of the welding of the component are also carried out using well established codes, with the simulations sometimes validated via measurements. Measurements are usually undertaken at locations where it is judged that the peak residual stresses occur. Therefore comparisons are often confined to limited locations. But this raises the question whether the simulated residual stresses at other locations are correct. To explore this, the work reported in this paper relies on introducing measured residual stresses into an elastic FE model of the welded component. These stresses are mapped into the model at the measurements locations. Then the FE analysis redistributes the initial stresses, with an iterative process introduced to ensure that the measured stresses are retained during redistribution. Examples are shown where agreement between measured and weld model predictions are good at the measurement locations and both the measured and weld model predictions satisfy global equilibrium. However, they do not agree at other locations. It is argued that additional measurements at other locations are required to validate the FE models of welding processes.

Operation of components at high temperature in power stations leads to the relaxation of residual stresses created in welded stainless steel cylinders. In this work a number of Esshete 1250 stainless steel cylinders containing girth welds and repair welds were manufactured. Two cylinders were then put to a furnace for 10,000hrs and 20,000hrs at 650°C. These conditions simulated the effects of aging. The residual stresses in the girth welds and repair welds before and after aging were measured using a number of methods based around the Deep Hole Drilling method. This paper describes the experiments carried out to obtain the through-wall distribution of stresses. It is evident that there was significant relaxation of the residual stresses due to aging. The peak tensile residual stress in girth welds was relaxed from 500MPa to 110MPa and the peak compressive residual stress in girth welds was relaxed from −301MPa to −135MPa after 10,000 hours at 650°C. The repair weld residual stresses were not only relaxed at the peak stresses but relaxed average levels from 220MPa to 140MPa for hoop stresses and from 180MPa to 145MPa for axial stresses. The implications of these findings are discussed in the context of future fracture tests.