Interpass Temperature — What It Is and Why It Matters
Interpass temperature is the temperature of the weld zone measured before depositing the next weld pass in a multi-pass joint. It is specified as both a minimum (to maintain preheat) and a maximum (to prevent overheating that degrades mechanical properties or corrosion resistance).
Maintaining minimum interpass temperature ensures the cooling rate remains slow enough to prevent hydrogen cracking and hard HAZ formation — the same purpose as the initial preheat. If the workpiece cools below the minimum interpass temperature between passes, it must be reheated before continuing.
Maximum interpass temperature limits exist primarily for stainless steels (where excessive heat causes sensitization and reduced corrosion resistance), quenched and tempered steels (where excessive heat softens the tempered microstructure), and low-temperature service applications. Exceeding maximum interpass temperature can require the welder to stop and wait for the area to cool before proceeding.
Frequently Asked Questions
How do I measure interpass temperature?
Use a contact pyrometer, infrared thermometer, or temperature-indicating crayon placed on the weld surface or adjacent base metal. Measure at the location specified by the code — typically on the face of the previous weld pass or the adjacent base metal. Verify before each new pass.
What happens if I exceed maximum interpass temperature?
On stainless steel, excessive heat between passes causes sensitization (chromium carbide formation) that destroys corrosion resistance. On quenched and tempered steel, excessive heat softens the HAZ below the required strength. If the maximum interpass temperature is exceeded, you must stop welding and wait for the area to cool before the next pass.