The inner surface of ferritic steel reactor pressure vessels (RPV) is clad with strip welded austenitic stainless steel primarily to increase the long-term corrosion resistance of the ferritic vessel. The strip welding process used in the cladding operation induces significant residual stresses in the clad layer and in the RPV steel substrate, arising both from the thermal cycle and from the very different thermal and mechanical properties of the austenitic clad layer and the ferritic RPV steel This work measures residual stresses using the deep hole drilling (DHD) and neutron diffraction (ND) techniques and compares residual stress data obtained by the two methods in a stainless clad coupon of A533B Class 2 steel. The results give confidence that both techniques are capable of assessing the trends in residual stresses, and their magnitudes. Significant differences are that the ND data shows greater values of the tensile stress peaks (~100 MPa) than the DHD data but has a higher systematic error associated with it. The stress peaks are sharper with the ND technique and also differ in spatial position by around 1 mm compared with the DHD technique.

Girth welded pipes such as those located offshore on platforms in the North Sea are subjected to highly corrosive environment. The need to consider welding residual stresses in the assessment of the fitness for service and damages to these pipes when investigating local corrosion damages across a welded region is therefore important for the operators of the platforms and the manufacturers of the pipes. This paper presents a review of work carried out to ascertain the welding residual stresses present within a thin-walled girth welded pipe mock-up made from steel API 5LX Grade 52. The mock-up was manufactured to replicate typical pipes used to convey gas, oil and water through the platforms. The mock-up was of diameter 762mm and of thickness 19mm. The incremental deep hole drilling (iDHD) technique and the contour method were applied to characterize the residual stresses in the weld and heat affected zone of the specimen. The results of these measurements are presented and compared to highlight agreements and discrepancies in the measured residual stress distributions using these different techniques. Most residual stress measurement methods are limited in terms of their stress and spatial resolution, the number of measurable stress tensor components and their quantifiable measurement uncertainty. In contrast, finite element simulations of welding processes provide full field distributions of residual stresses, with results dependent on the quality of the input conditions available. As measurements and predictions are not often the same, the true residual stress state is therefore difficult to determine. In this paper, through-thickness residual stress measurements are made using the contour and iDHD methods and these residual stresses measured using the iDHD technique are then used as input to a residual stress mapping technique provided within a finite element analysis to reconstruct the residual stress field in the whole specimen. The technique is applied iteratively to converge to a balanced solution which is not necessarily unique. The solution can then be reused for further simulations and residual stress analyses, such as corrosion simulation. Results of the reconstruction are presented here.

Most residual stress measurement methods are limited in terms of their stress and spatial resolution, number of stress tensor components measured and measurement uncertainty. In contrast, finite element simulations of welding processes provide full field distributions of residual stresses, with results dependent on the quality of the input conditions. Measurements and predictions are often not the same, and the true residual stress state is difficult to determine. In this paper both measurements and predictions of residual stresses, created in clad nuclear reactor pressure vessel steels, are made. The measurements are then used as input to a residual stress mapping technique provided within a finite element analysis. The technique is applied iteratively to converge to a balanced solution which is not necessarily unique. However, the technique aids the identification of locations for additional measurements. This is illustrated in the paper. The outcomes from the additional measurements permit more realistic and reliable estimates of the true residual state to be made. The outcomes are compared with the finite element simulations of the welding process and used to determine whether there is a need for additional input to the simulations.

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.

Girth welded pipes, such as those located offshore on platforms in the North Sea, are subjected to highly corrosive environment. The need to consider welding residual stresses in the assessment of the fitness for service and damages to these pipes when investigating local corrosion damages across a welded region is therefore important for the operators of the platforms and the manufacturers of the pipes. This paper presents a review of work carried out to ascertain the welding residual stresses present within a thin-walled girth welded pipe mock-up made from steel API 5LX Grade 52 before and after reduction of the wall thickness. The mock-up was manufactured to replicate typical pipes used to convey gas, oil and water through the platforms. The mock-up was of diameter 30” and of thickness 19mm. The incremental deep hole drilling (iDHD), contour, hole drilling, XRD, and ultrasonic technique were applied to characterise the residual stresses in the weld and heat affected zone of the specimen. The residual stresses were then measured during the manufacture of a groove located on the weld at the ID and were compared to an FE prediction. Ultrasonic measurements were then carried out on the outer surface of the pipe and show a significant increase in the residual stress and could be used to monitor the changes in the residual stress caused by internal corrosion.