Control Requirements for Interpass Temperatures and On-Site Management Standards

I. Definition of Interpass Temperature

Interpass temperature is the minimum temperature that you must keep in the previous weld and the heat-affected zone. This is between finishing the previous weld and starting the next weld during multi-pass or multi-layer welding. Note that interpass temperature and preheating temperature are two different process concepts. You must tell them apart during on-site work to avoid confusion.

II. Principles for Selecting Interpass Temperatures

Interpass temperature values are not fixed. You must decide them based on many factors. These factors include base metal type, plate thickness, joint configuration and welding method. For example, materials that tend to harden easily (like low-alloy high-strength steel) need a higher interpass temperature. This higher temperature helps to keep the weld in the high-temperature zone longer. This then improves the microstructural toughness of the heat-affected zone. For materials that are sensitive to heat (like aluminum alloys), you should keep the interpass temperature low. This low temperature stops welding distortion and reduces oxide film formation.

III. Key Considerations

1. Include in Process Documentation and Strictly Adhere to

Interpass temperature is a core parameter in welding process specifications. You must clearly write it in the welding procedure qualification (WPS/PQR) documents. On-site construction must follow the qualified process parameters closely. You cannot change them without permission.

2. Standardize Temperature Measurement and Maintain Records

You should measure interpass temperature with a temperature pen or infrared thermometer. You take measurements on the surface of the previous weld bead and in the heat-affected zone. You must record all measurement data correctly. You also need to archive it for future quality checks.

3. Tailor Temperature Settings to Material; Do Not Apply Generic Standards

Different materials have very different interpass temperature requirements. You cannot use the same experience for different materials during construction. Common situations are as follows:

Note: The interpass temperature ranges in this document are for general reference only. In real engineering work, you should follow the relevant welding procedure qualification (WPS/PQR) documents for the specific project.