The framework for this document is based upon the American Welding Society ANSI/AWS D10.10-90, Recommended Practices for Local Heating of Welds in Piping and Tubing. During the process of revising this AWS document, it was recognized that it might be more appropriate to prepare a separate document pertaining recommended practices for local heating of welds in pressure vessels. At the same time, a request was received to prepare a guideline regarding postweld heat treatment of repairs for heavy wall hydroprocessing reactors.This request was made by a joint industry project on aging hydroprocessing reactors.Additionally, for the last several years, an ASME Boiler and Pressure Vessel Code Ad Hoc Task Group on Local PWHT, operating under the Section VIII Subgroup Fabrication and Inspection, has been developing requirements for local PWHT.The confluence of these three activities is responsible for the development of this document. The document in draft form has been circulated for review and commenting by various communities since May 1997.They are: the Pressure Vessel Research Council, ASME Board of Pressure Technology Codes and Standards Task Group on local PWHT, AWS Subcommittee D10P on local heat treating of pipework, and IIW Commission XI on pressure vessels, boilers, and pipelines.During the review and commenting period, a new revision on the requirements (paragraphs UW-40 and AF-410, see Appendices A and B) for local PWHT in Section VIII of ASME Boiler and Pressure Vessel Code was issued in July 1998.