Comparative Study for Stresses in Nozzle and Flange Welds Generated During Conventional Pressure Testing and Local Pressure Testing Using Bolted Devices

Weld repairs and alterations of pressure vessels and piping built to ASME codes may require pressure testing to prove the integrity of the weld and/or design. Conventional hydrostatic pressure testing requires filling an entire vessel or piping system with water and pressurizing it to the test pressure. In recent years, several designs were developed to employ bolted devices to perform local pressure testing of flange-to-nozzle, flange-to-pipe, and nozzle-to-shell attachment welds. Due to the cost and equipment downtime associated with performing a full conventional pressure test and the desire to reduce repair costs, several petrochemical companies adopted the use of such devices. The purpose of this paper is to compare the stress values and stress distribution associated with conventional and local pressure testing techniques. The advantages and disadvantages of both approaches are discussed and the conclusions are supported by a practical example.