10.5 PREHEATING

Preheat can be applied using several different techniques, but the most
common techniques used in pipe and tank fabrication are electrical resistance
coils, or an oxy-acetylene or natural gas torch. Good practice is to uniformly
heat an area on either side of the weld joint for a distance three times the
width of the weld. Preheat should be applied and extend to at least 2 in. (50.8
mm) on either side of the weld to encompass the weld and potential heat
affected zone areas. Inspectors shall exercise caution when welding metals
of different chemistries or preheat requirements ensuring that preheats for
both metals are in accordance with codes and the WPS documentation.
Typically, the metal with the highest preheat requirement governs.