Estimate a practical maximum interpass temperature for multipass welding based on material type, thickness, welding process and joint conditions.
Interpass temperature is the temperature of the weld area and adjacent base metal immediately before the next welding pass is deposited. It becomes particularly important during multipass welding because heat accumulates as successive passes are deposited.
A welding procedure can specify both a minimum preheat temperature and a maximum interpass temperature. The minimum temperature helps control cooling and cracking risk, while the maximum temperature limits excessive heat accumulation.
The correct interpass limit depends strongly on the material and applicable welding procedure. Stainless steels, duplex stainless steels, nickel alloys and heat-treated steels can have substantially different temperature limitations.
During multipass welding, each new weld pass adds heat to the joint. If the temperature becomes too high, the accumulated thermal exposure can change the resulting microstructure and mechanical properties.
For some carbon and low-alloy steels, excessive interpass temperature can alter cooling behavior and affect strength, toughness or hardness. For stainless steels, controlling heat exposure can help limit unwanted metallurgical changes and corrosion-related problems.
Duplex stainless steels require particularly careful control because their phase balance can be affected by welding thermal cycles. The acceptable interpass temperature is therefore normally taken directly from the qualified procedure or applicable material/welding standard.
| Material | Indicative Maximum Range | Why Control Matters |
|---|---|---|
| Carbon / mild steel | ~250–300°C | Controls accumulated heat and cooling behavior in multipass welds. |
| Low-alloy steel | ~200–250°C | Heat treatment condition, strength and toughness may require tighter control. |
| HSLA steel | ~150–200°C | Excessive heat can affect strength and heat-affected-zone properties. |
| Austenitic stainless steel | ~150–200°C typical reference | Limits excessive heat exposure and helps control metallurgical effects. |
| Duplex stainless steel | Often ~150°C or lower | Phase balance and corrosion performance are sensitive to welding thermal cycles. |
| Martensitic stainless steel | Grade-specific | Preheat, interpass and post-weld heat treatment can be closely linked. |
| Nickel alloys | Often comparatively low | Excessive interpass temperature can affect metallurgical and corrosion performance. |
| Term | When It Is Measured | Purpose |
|---|---|---|
| Preheat temperature | Before welding begins | Maintains a minimum starting temperature and controls cooling rate. |
| Interpass temperature | Immediately before the next weld pass | Controls accumulated heat during multipass welding. |
| Maximum interpass | Before subsequent passes | Prevents the weld from becoming excessively hot. |
| Post-weld heat treatment | After welding | Provides controlled thermal treatment when required by the material or procedure. |
Heat input and interpass temperature are related but are not the same thing. Heat input describes the energy introduced by the welding process per unit length, while interpass temperature describes the temperature condition of the joint between passes.
A higher heat input can increase the amount of thermal energy delivered to the workpiece. Repeated passes can also cause heat to accumulate, particularly when the joint is large or cooling between passes is limited.
A simplified arc-energy relationship is commonly expressed using welding voltage, current, travel speed and process efficiency. Actual heat input calculations should follow the formula specified by the applicable welding procedure or standard.
| Material | Main Concern | Temperature Control |
|---|---|---|
| Carbon steel | Cooling rate, hardness and cracking | Maintain required minimum preheat while staying below maximum interpass. |
| Low-alloy steel | Hardening and toughness | Follow qualified preheat, interpass and post-weld requirements. |
| Austenitic stainless | Excessive heat exposure | Usually avoid unnecessary high interpass temperatures. |
| Duplex stainless | Ferrite/austenite phase balance | Use the specific interpass limit in the qualified procedure. |
| Martensitic stainless | Hardening and cracking | Preheat and interpass control are usually grade-specific. |
| Nickel alloys | Metallurgical and corrosion performance | Use controlled interpass temperatures and qualified procedures. |
The temperature should be measured at the location and distance specified by the applicable welding procedure or standard. Common methods include temperature-indicating crayons, contact thermometers, thermocouples and suitable infrared instruments.
Surface condition and emissivity can affect infrared measurements. For critical fabrication, the measurement technique should be suitable for the material and comply with the governing procedure.
The welder should verify the temperature before depositing the next pass. If the measured temperature is above the specified maximum, welding should be paused until the joint cools to the required range.
What is interpass temperature? Interpass temperature is the temperature of the weld area and adjacent base metal immediately before the next welding pass is deposited.
What is maximum interpass temperature? It is the highest temperature permitted before depositing the next weld pass according to the welding procedure or applicable standard.
Why is maximum interpass temperature important? It limits accumulated heat during multipass welding and helps maintain the required weld and heat-affected-zone properties.
Is interpass temperature the same as preheat? No. Preheat establishes the minimum temperature before welding, while interpass temperature is checked between welding passes.
Can the interpass temperature be too high? Yes. Excessive heat can change microstructure, reduce mechanical properties in some materials, affect corrosion resistance and alter the intended welding thermal cycle.
What is a typical interpass temperature for stainless steel? There is no universal value. Many stainless-steel procedures use relatively low maximum interpass temperatures, but the exact limit depends on the grade and welding procedure.
What about duplex stainless steel? Duplex stainless steel requires careful thermal-cycle control because its ferrite/austenite balance can be affected by welding. The applicable qualified WPS should determine the maximum interpass temperature.
Does heat input affect interpass temperature? Yes. Higher heat input can contribute to greater heat accumulation, although actual interpass temperature also depends on thickness, joint geometry, pass sequence, cooling conditions and ambient conditions.
Can I use this calculator for code compliance? No. It is a preliminary reference tool. The applicable welding code, material specification, project specification and qualified WPS take precedence.
What should I do if the measured temperature exceeds the WPS limit? Do not deposit the next pass until the joint returns to the specified temperature range, following the welding procedure and applicable safety requirements.