What Is a PWHT Soak Time Calculator?
Post weld heat treatment (PWHT) holds a welded part at an elevated temperature for a set time to relieve residual stress from welding and temper hard heat-affected zones. This calculator applies the standard rule-of-thumb basis — one hour of soak time per inch of governing thickness — and applies a minimum hold time floor so thin sections still get adequate treatment.
Soak time is the time held at temperature, not the full cycle time; ramp-up and controlled cool-down are separate stages with their own rate limits that this calculator does not cover.
How to Read Your Results
Required Soak (Hold) Time
The larger of the 1-hour-per-inch calculation and the minimum hold time you selected — this is the time to hold at the PWHT temperature.
Time From 1 Hr/In Rule
The soak time based purely on thickness, before any minimum is applied.
Selected Minimum Hold Time
The code-style floor you chose; thin parts are held at least this long even though the 1 hr/in rule alone would call for less.
Real-World Example
A fabricator needs to stress-relieve a 2-inch-thick pressure vessel nozzle weld, with a 30-minute minimum hold time specified by the procedure.
| Item | Value |
|---|---|
| Governing thickness | 2.00 in |
| 1 hr/in calculation | 2 hr 0 min |
| Minimum hold time | 30 min |
| Required soak time | 2 hr 0 min |
Because 2 hours from the thickness rule is already longer than the 30-minute minimum, the 1 hr/in rule governs and the part must soak for 2 full hours at temperature.
Tips for Planning PWHT
- Use the governing (thickest) dimension in the joint, not an average, unless your code says otherwise.
- Soak time is separate from ramp and cool rates, which are also limited (often by degrees per hour per inch) to avoid thermal shock.
- Very thick sections can be subject to a reduced rate or capped total time in some codes — check the specific code table for material and thickness range.
- Always follow the qualified PQR/WPS for the actual material, not just a rule of thumb, for code-stamped work.
Related Calculators
Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team