The Effects Of Performing Local Pwht And Considerations

CHAPTER 1 Literature and Previous Work Introduction and Related Research There is a common practice to perform post weld heat treatment when performing alterations or repairs to pressure vessels that have been stress relived prior to being commissioned. This research paper is the study of the consequences of performing local PWHT and considerations that need to be taken when determining what type of stress relieving is to be performed to meet code requirements. Post weld heat treatment is an effective way to minimize weld residual stresses in pressure vessels and piping equipment. PWHT is a required for carbon steels above a code defined thickness threshold and other lo-allow steels to mitigate the propensity for crack initiation and ultimately, brittle fracture, and is often employed to mitigate stress corrosion cracking due to environmental conditions. Performing local PWHT following component repairs or alterations is often more practical and cost effective than heat treating an entire vessel or a large portion of the pressure boundary. Spot or bul ls eye configurations are often employed in industry to perform PWHT following local weld repairs to regions of the pressure boundary. Both the ASME Boiler and Pressure vessel code and the National Board inspection code permit the use of local PWHT around nozzles or other pressure boundary repairs or alterations. Additionally, welding research council bulletin 452 offers detailed guidance relating to local PWHT and