Calculator Inputs
Enter chemistry, thickness, hydrogen level, restraint, process, and ambient conditions. The form uses a 3-column large-screen grid, 2-column medium grid, and 1-column mobile stack.
Plotly Graph
The chart shows how the estimated recommended preheat shifts as thickness changes while keeping the rest of your inputs fixed.
Example Data Table
These example jobs show how chemistry, restraint, hydrogen, and section size influence preheat planning.
| Case | CEIIW | Thickness (mm) | Hydrogen | Restraint | Ambient (°C) | Recommended Preheat (°C) |
|---|---|---|---|---|---|---|
| Low-carbon plate | 0.334 | 12 | H4 | Low | 18 | 30 |
| Structural joint | 0.521 | 25 | H8 | Medium | 5 | 145 |
| Heavy restrained weld | 0.58 | 40 | H16 | High | 0 | 235 |
| Repair weld | 0.737 | 18 | H4 | High | 12 | 195 |
Formula Used
Carbon Equivalent, CEIIW
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Base Preheat Estimate
Base Preheat = 25 + 250 × max(0, CE − 0.35) + 0.35 × Thickness(mm)
Recommended Preheat
Recommended = Base + Hydrogen + Restraint + Ambient + Process + Joint + Criticality + Heat Input adjustments, rounded to the nearest 5°C.
This calculator is an engineering estimate for planning and comparison. It is not a substitute for a qualified WPS, PQR, project specification, code requirement, or consumable manufacturer recommendation.
- Higher carbon equivalent raises hardenability and cracking sensitivity.
- Greater thickness raises cooling severity and heat demand.
- Higher hydrogen classes and restrained joints increase cracking risk.
- Low ambient temperature increases the preheat requirement.
- Repair welds and high-consequence service receive added conservatism.
How to Use This Calculator
- Enter the weld metal chemistry values or the base material chemistry values you are assessing.
- Provide section thickness in millimeters and current ambient temperature in Celsius.
- Select hydrogen class, restraint level, process, joint type, and service criticality.
- Enter estimated heat input for the planned welding procedure.
- Press Calculate Preheat to show the result above the form.
- Review the recommended preheat, interpass suggestion, factor table, and warnings.
- Use the Plotly graph to compare preheat sensitivity over thickness changes.
- Download the result as CSV or PDF for reports, planning sheets, or weld packs.
FAQs
1. What does welding preheat do?
Preheat slows cooling, reduces hardness in the heat-affected zone, helps hydrogen diffuse out, and lowers the chance of cold cracking in restrained or thicker weldments.
2. Why is carbon equivalent important?
Carbon equivalent combines alloying effects into one value. A higher CE usually means greater hardenability and a higher risk of cracking, so more preheat is often required.
3. Does thicker material always need more preheat?
Usually yes. Thick sections extract heat faster and create steeper cooling rates, so the weld and heat-affected zone often need more starting temperature to stay crack-resistant.
4. How does hydrogen class affect the result?
Higher diffusible hydrogen levels raise cracking risk. The calculator adds more temperature for higher hydrogen classes because dry consumables and low-hydrogen practice are critical controls.
5. Should I use this result instead of a WPS?
No. This tool helps estimate and compare conditions. The qualified WPS, applicable code, customer specification, and filler manufacturer guidance should always govern production welding.
6. Why does ambient temperature change preheat?
Cold surroundings increase heat loss from the joint. That faster cooling can raise hardness and cracking risk, so the calculator adds a cold-weather penalty.
7. What is interpass temperature here?
It is a suggested control level above the starting preheat to help maintain stable thermal conditions during multi-pass welding. Actual limits should match your procedure qualification.
8. Can this calculator be used for repair welding?
Yes, but repair welds are riskier because of restraint, unknown history, and local hard zones. The calculator adds conservatism, yet repair work should be reviewed carefully.