In October 1999, ANSI approved AWS D10.10, “Recommended Practices for Local Heating of Welds in Piping and Tubing.” The following year, that document became the basis for the Welding Research Council Bulletin WRC-452 for pressure vessels. These documents provide guidance in thermocouple placement, heated band (HB) width guidelines, maximum allowable temperature gradients, and gradient control band (GCB) insulation guidelines. In 2009, AWS reaffirmed D10.10.
Often, a local spot or “bull’s eye” PWHT configuration is allowed for PWHT of attachment or repair welds. Both the ASME Boiler and Pressure Vessel Code (BPVC) and the National Board Inspection Code (NBIC) permit the use of local PWHT around nozzles or other pressure boundary repairs or alterations. In fact, the NBIC is the only American governing code that has adopted WRC-452 HB and gradient guidelines as code requirements.
The results of ignoring these recommended practices and inadequately engineering a PWHT can be:
- Inadequate heated band (HB) width
- Excessive axial temperature gradients
- Inattention to thermal growth constraints
- Excessive thermally-induced residual stresses
- -- Plastic distortion
- -- Stress cracking
TEAM is the only company in the on-site heat-treating industry with an in-house Technical Support Group (TSG), professional engineers, and direct access to Quest Integrity stress analysts to assess complex PWHTs by providing:
- Zick analyses of shell stresses in horizontal vessels on saddle supports
- Weight & wind load analyses (WAWLA’s) of leeward shell stresses in vertical vessels
- Finite element analyses (FEA’s) of weldment residual stresses at geometric discontinuities
TEAM’s QA program demands that all complex, nuclear, and Creep Strength Enhanced Ferritic (CSEF) steel PWHT projects are deemed critical jobs, requiring a multi-disciplined review by TEAM engineering and technical support personnel. Consequently, each critical job is closely examined to minimize risks and ensure technical success.
TEAM has produced over 24 Generic Field Procedures (GFP’s) and Standard Practices (SP’s), which together with an unsurpassed training program, fosters repetitive high-quality heat-treating practices. The company’s TSG works with client engineering and operational personnel to develop custom heat-treating procedures, in accordance with code and client requirements to coordinate field implementation.
TEAM provides the widest variety of heating methods available to ensure that the safest and most effective method is employed to achieve PWHT goals. This equipment includes:
- Low-voltage flexible ceramic pad (FCP) electric resistance heating systems
- Wireless SCADA PLC SmartHeat control systems
- High-velocity combustion heating systems
- High voltage radiant heating systems
- Induction heating systems
- Temporary and permanent furnaces
PWHT is a code requirement, a weldment enhancement, and a technical challenge. When stakes are high and time is pressing, you want to ensure you work with a company that can solve your problems. TEAM’s professional engineers and network of trained heat-treating technicians provide common sense and technical savvy borne from years of hands-on experience.
To learn more, visit TeamInc.com or call 1-800-662-8326.
