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Recommended Practices for Local Heating of Welds in Piping and Tubing
1. Scope
These recommended practices describe several methods of applying controlled heat to weld joints and a limited volume of base metal adjacent to the joints, as opposed to heating the complete weldment in a furnace or oven. This standard makes use of both U.S. Customary Unitsand the International System of Units (SI). The measurements are not exact equivalents; therefore, each system must be used independently of the other without combining values in any SI Units are listed second in parentheses ( ) when used in the text.
2. Reference Documents
Extensive reference to local heating requirements found in common piping codes, standard and practices is made to aidthe user of this document. These referenced codes, standards and practices are listed below. Except for bake-out and postheating, specific hold temperature and time requirements are not discussed.
3.1. Piping Fabrication Codes
(1) Power Piping (ANSI/ASME B31.1), 1995 Edition, with addenda through 1997.
(2) Process Piping (ANSI/ASME B31.3), 1996 Edition, with addenda through 1997.(3) ASME Boiler and Pressure Vessel Code, Section III, Division I–Subsection NB, Class I Components Rules for Construction of Nuclear Power Plant Components, 1998 Edition. (Note: Although direct reference is made to Subsection NB its related paragraphs, Subsection NC and ND for Class 2 and 3 components have essentially the same requirements.)
(4) British Standard Specification for CarryingFluids (BS 2633), 1987 Edition, with Amendments to No. 2 July 1992.

3.2. Repair Codes
(1) NBIC National Board Inspection Code (ANSI/NB B-23), 1995 Edition, with Addenda through 1996.
(2) API Piping Inspection Code [Inspection, Repair, Alteration, and Rerating of In-Service Piping Systems] (ANSI/API 570), June 1993 Edition, with Supplements through #1, January 1995.
3.3.Recommended Practices Regarding Service Environment
(1) Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments (NACE RPO 0472-95), 1995.
(2) Avoiding Environmental Cracking in Amine Units (ANSI/API 945), 1990.

3. Introduction
These recommended practices consider the various issues associated with localheating of welds in piping and tubing. They specifically address application of controlled heat to the weld metal, heat-affected zone (HAZ), and a limited volume of base metal adjacent to the weld, as opposed to heating the entire component (piping or tubing system) in a furnace or oven. The recommended practices generally address issues associated with circumferential butt welds. As such, primaryemphasis is given to considering local 360-degree band heating. However, limited consideration of local spot heating is also provided. Although aimed at local heating, various issues common to both local and furnace heating are also discussed.
In the manufacture, field fabrication and/or repair of piping and tubing, it may be necessary to heat components before welding (bake-out or preheating)between passes (interpass heating) or after welding (postheating or postweld heat treatment [PWHT]). This document addresses all of these purposes for heating, with the main emphasis on PWHT.
Although heating of piping and tubing may be performed in a furnace, component size, convenience, or use of a process such as preheat/interpass heating may preclude the use of a furnace. In such cases, the weldand adjacent material may be locally heated by one of the methods discussed in these recommend practices. Local heating is also very common during field fabrication and/or repair of components. The method used will often be determined by the availability of equipment, the accessibility of the area to be heated, constraints imposed by adjacent materials or components, and the type of heating...