Interpass Temperature Calculator for Construction Welding

Example Data Table

Formula Used

Cooling model: This calculator uses a Newton cooling approximation to estimate temperature drop between passes:

T(t) = Tamb + (T0 − Tamb) · e^−k·t

• Tamb is ambient temperature.
• T0 is temperature just after the pass (measured or estimated).
• k is the cooling coefficient (1/min), adjusted by thickness, wind, and joint.
• t is the time between passes (minutes).

Wait time: If you set a maximum or target, the required wait is computed by rearranging the equation:

t = −ln((Tlimit − Tamb)/(T0 − Tamb)) / k

If you use estimation mode, T0 is approximated from preheat, heat input, thickness, material factor, and process efficiency.

How to Use

1. Select your temperature unit and thickness unit.
2. Choose measured mode and enter Tamb, T0, Δt, thickness.
3. Or choose estimation mode and enter preheat and heat input.
4. Pick material and joint type; add wind if present.
5. Enter max/min limits from your procedure if available.
6. Press Submit to view interpass temperature and status.
7. Download CSV or PDF to keep inspection records.

Interpass Temperature Guidance Article

1) Purpose of interpass control

Interpass temperature is the base-metal temperature measured just before the next weld pass. Controlling it improves bead shape, limits distortion, and reduces the risk of metallurgical problems that can reduce service life. On structural and piping work, it supports consistent mechanical properties across the joint.

2) How interpass differs from preheat

Preheat is the minimum starting temperature before welding begins, while interpass is the temperature between passes during multi-pass welding. A procedure may require both: preheat prevents rapid cooling and cracking, and interpass prevents overheating that can reduce toughness or change hardness beyond acceptance limits.

3) Practical measurement on site

Use temperature crayons, contact thermometers, or calibrated infrared tools when permitted. Measure on clean metal at a consistent distance from the weld toe and on the same side each time. Record the time, location, and method so readings can be compared and audited during inspections.

4) Typical ranges and limits

Projects often specify a maximum interpass to protect toughness and minimize excessive grain growth in steels. Common maximums on carbon and low-alloy work may fall around 150–250 °C depending on code, thickness, and consumables. Stainless and aluminum procedures can differ, so always follow the qualified limits.

5) Cooling drivers: thickness, wind, and joint

Thicker sections act as heat sinks and cool more slowly near the joint, while thin members cool quickly and may need tighter timing. Wind and drafts increase convection and can drop temperature faster than expected, especially on exterior work. Joint geometry also changes heat flow and cooling behavior.

6) Using a cooling model for planning

This calculator applies a Newton cooling model to estimate the temperature at a chosen time between passes. When you also enter a maximum or target, it can estimate a wait time that supports scheduling, crew coordination, and controlled rework decisions. Measured inputs generally produce the most reliable results.

7) Documentation and quality records

Interpass logs help demonstrate compliance with procedure requirements during client reviews and third-party audits. Record ambient conditions, thickness, weld process, and actual measured values. Exporting results to CSV and PDF supports daily reports and traceability for critical joints and repairs.

8) Field tips for stable interpass control

Keep a consistent pass sequence and avoid long delays that allow the joint to cool below minimum limits. If the temperature is too high, allow controlled cooling rather than forced cooling unless the procedure permits it. If too low, reheat only within approved methods and document the action.

FAQs

1) Why does maximum interpass temperature matter?

Excessive interpass heat can reduce toughness, increase distortion, and alter hardness in heat-affected zones. A maximum limit helps keep metallurgical properties aligned with the qualified procedure and code acceptance requirements.

2) Where should I measure interpass temperature?

Measure on clean base metal near the weld, typically a consistent distance from the toe. Use the same location approach for every pass to keep readings comparable and defensible during inspection.

3) Can I rely on estimation instead of measuring?

Estimation is useful for planning, but measurement is preferred for compliance and accuracy. Field conditions like wind, fit-up, and actual heat input can change cooling behavior compared with assumptions.

4) What if ambient temperature is close to my maximum limit?

If ambient is near or above the maximum, cooling below the limit may be difficult. Consider shading, reducing heat input within procedure allowances, improving ventilation control, or adjusting sequence under an approved procedure change.

5) How do wind and drafts affect interpass temperature?

Air movement increases convection and can cool the joint faster than expected, especially on thin material. Logging wind conditions and using wind breaks can stabilize readings and improve repeatability.

6) What is the cooling coefficient k in this calculator?

k represents overall cooling rate per minute in the Newton model. It is influenced by material type, thickness, joint form, and wind. You can override it if you have site-calibrated data.

7) Does this replace a qualified welding procedure?

No. It supports planning and documentation, but the qualified procedure and applicable code control acceptance. Always follow specified measurement methods, limits, and corrective actions for your project.