Q. Postweld heat treatment?
When the equipment data sheet specifies post-weld heat treatment either for service conditions or code requirements, welding, hammering (peening), or deformation are not permitted after post-weld heat treatment. All internal and external attachments, clips, insulation studs, nameplate bracket, and the like must be welded to the unit before post-weld heat treatment.
If the Seller plans to use a local post-weld heat treatment, a detailed description of the local heat treatment procedure must be submitted to the OWNER for review and acceptance prior to use. Attach two thermo-couples each to the outside and inside surfaces of the equipment.
The use of exothermic kits is not acceptable.
In addition to the requirements of the applicable code, a continuous record of the temperature indicated by the thermocouples shall be made on recorder charts. A copy of these charts shall be included in the fabrication and test records furnished to the OWNER.
All welds to P-5 steel shall be post weld heat treated.
Flame impingement on parts being heat treated is prohibited.
When post-weld heat treatment of P-3 through P-6 materials is required, it shall be performed immediately after welding. If impractical to do so, take necessary steps to prevent cracking.
At least two thermocouples shall be in contact with the materials in each furnace load to monitor the PWHT temperature.
Intermediate stress relief (ISR), if required, shall be 621°C (1150°F). Low temperature (approximately 316°C (600°F)) stress relief is not acceptable.
The lower post-weld heat treatment temperature permitted by ASME Section VIII, Table UCS-56 or Table AF-402.2 are not acceptable.
All heat treatment procedures must be submitted to OWNER for review prior to implementation.
All machined surfaces must be protected from oxidization during heat treatment.
Each equipment receiving PWHT shall be painted on both sides of the equipment in lettering at least 50 mm (2") high, "POSTWELD HEAT TREATED, DO NOT WELD, HAMMER, DEFORM OR STRIKE ARCS". The paint used must be compatible with both the primer and the finish paint.