Interpass temperature: meaning and how to check it

Use this diagram

Copy this HTML to show the diagram with a credit link<img src="https://filletgauge.com/charts/filletgauge/interpass-temperature.svg" alt="A part-finished multipass groove weld with a thermometer near the joint, beside a graph of joint temperature against time that is preheated above the minimum before the first pass, rises with each pass and falls between them, with dots marking the reading just before each new pass, between a dashed WPS minimum and a dotted WPS maximum" width="100%"><p><a href="https://filletgauge.com/guides/interpass-temperature?utm_source=embed&amp;utm_medium=referral&amp;utm_campaign=figure_embed&amp;utm_content=interpass-temperature.svg">The dots are the interpass readings. No values are shown: the WPS supplies them. by Fillet Gauge</a></p>

How to check interpass temperature

1. Read it just before the next pass. The number that counts is the one taken right before the arc starts again, not the peak right after a pass.
2. Read it where the procedure says. Codes and WPSs say where on the base metal to take the reading, measured from the joint. Reading on the weld bead itself gives a different number.
3. Use a suitable tool. Temperature-indicating crayons melt at a set temperature, contact thermometers read the surface directly, and infrared thermometers read from a distance but need the right surface and distance to be trusted.
4. Compare with the WPS. If the joint is below the minimum, it needs heating back up. If it's above a maximum, the welder waits.

Common mix-ups

• Interpass versus preheat. Preheat is the temperature before the first pass. Interpass is the temperature before each later pass. A procedure often sets the minimum interpass equal to the minimum preheat, but they're two separate checks.
• Maximum interpass. Not every procedure has one. Quenched and tempered steels, some stainless steels and jobs with toughness requirements often do, because running hot can spoil the properties of the heat-affected zone.
• Interpass versus postweld heat. Holding the joint warm after welding, or heat treating it later, are different operations with their own rules.
• Per pass, not per layer. The check happens between passes, so a layer of three side-by-side beads means three readings, not one. The weld pass vs weld layer page shows the difference.

Interpass temperature on the CWI exam

Interpass and preheat are in Definitions and Terminology, at least 12% of Part A, and checking them during welding is Welding Application and Control, at least 9% of Part A. Part A is closed book.

On Part B, preheat and interpass are entries on the procedure documents. Procedure and Performance Qualifications is at least 28% of the practical, and checking a recorded temperature against a WPS is the kind of task that domain covers.

On a D1.1 Part C, minimum preheat and interpass for prequalified procedures are in Clause 5, and their application in fabrication in Clause 7. Read the values in your own copy; none are given here.

Practice it

The metallurgy cards in the CWI Part A flashcards drill preheat, interpass temperature and why a maximum can matter. The heat terms sit next to the joint and weld terms in the welding terms glossary.

Got the heat terms? Check the rest of Part A

Take the free 10-question check. It's weighted to the Part A outline, scored by domain and needs no signup, so you see which domain costs you the most points. The Part A course then gives you a lesson on every exam subject, two full-length timed practice exams, and a worked explanation with every answer.

Sources

Show the list

• AWS bookstore, terminology and symbols listing, American Welding Society. Retrieved 20 Oct 2026.
• CWI Part A Fundamentals Examination Information, American Welding Society, Rev. 03.01.2024. Retrieved 20 Oct 2026.
• AWS B5.1:2025, Specification for the Qualification of Welding Inspectors, American Welding Society, Tables 5.1 and 8.1. Retrieved 20 Oct 2026.