Analysis Of Welding Residual Stresses Of Pressure Relief Valve Seats And Study Of The Effect Of Re-Seat Impact

Pressure relief valves (PRVs) or safety valves are a kind of safety protection facility. Its valve clack, disc holder and stem keep in the close state under the pressure from pipes and vessels. With the pressure increasing to the set pressure, the sealing facility would be lifted and the medium will be released to keep the equipment from over-pressure. PRVs should have good sealing performance in the normal state, but also should keep it after multi-impacts. Some manufacturing damages, like cracks and inclusions, are the primary reason of making the sealing performance failure, so for the requirements of good sealing performance, this article mainly investigates the revolution of residual stresses during the manufacturing process, including as-welded state, post weld heat treatment, final machining, and multi-impacts. For experiments, we use the infra-red imaging and thermocouples to measure temperature, the neutron diffraction to measure residual stresses, and also devise a simple multi-impact drop weight device to model the re-seat process of PRVs. For simulations, we use the commercial software Abaqus to simulate the whole manufacturing process. At the same time, we compare the simulated results with the experimental results, so that we can verify the exactness of simulation. The main conclusions are shown as follows:(1) During the two-pass welding process, owing to the influence of arc extinguishing, the arcing starting position experiences three typical thermal cycles, and the second measurement points in the direction experience the slight thermal cycles which could be omitted. And all the other positions all have two typical thermal cycles;(2) For the nine measurement points, the residual stresses are tensile after the welding, however, after the post weld heat treatment, the residual stresses decrease greatly. In addition, after the final machining, the regions are all subject to the tensile stresses except that axial and radical stresses near the inner surface are compressive stresses.(3) During multi-impact model, we firstly analyze the experimental results, which are meanwhile compared with the simulated results; and then we study the effect of the different impact parameters (like impact velocity, impact numbers and impact time) on the redistribution of residual stresses. It can be found that as the increase of impact numbers, the residual stresses tend to stay the same. Also for the one-impact case, the residual stresses for three directions decrease with the increase of impact velocity and impact time.