Interpass Temperature

Interpass temperature is the temperature of the weld zone, previously deposited weld metal, and adjacent base metal, measured immediately before the next weld pass in a multi-pass weld. Welding procedures control it as a minimum limit, maximum limit, or both; the minimum is tied to preheat, while the maximum prevents overheating the joint and heat-affected zone.

In a CNC fabrication cell, interpass temperature is checked between beads in multi-pass welds before the next arc is struck. The control point is the weld metal or joint area on the same side as the next pass, verified with contact crayons, thermocouples, or infrared pyrometers. The goal is to keep cooling slow enough to avoid brittle HAZ structures like martensite in carbon steels, while preventing overheating that causes grain coarsening, reduced toughness, sensitization in stainless steels, or phase imbalance in duplex grades. In practice, the welder pauses until the joint cools to the procedure limit, or holds it above a minimum preheat-related threshold when hydrogen cracking is a concern. Too hot degrades weld metallurgy; too cold can trap hydrogen or create hard, crack-prone structures.