Welding Interpass Temperature Control

Interpass temperature control is a process of controlling the temperature of the deposited weld metal between specified limits during multipass welds. The lower limit is usually the same as the minimum preheat temperature, and accomplishes the same functions. However, an upper limit is also relevant (especially when utilizing high heat input processes) to prevent the weld metal from becoming too hot during subsequent weld passes. If the metal is allowed to get too hot during subsequent welding passes, the following detrimental effects can occur:

• Excessive grain growth of the weld metal and HAZ can adversely affect the impact properties of carbon and alloy steel weldments.
• Carbon and low-alloy steels can experience precipitation of nitrides (called blue embrittlement) which adversely affects their impact properties.
• Austenitic stainless steels (such as the 300 series SSs) can lose corrosion resistance due to excessive sensitization during slow cooling.
• Columbium stabilized austenitic SSs (such as Type 347 SS, Incoloy 825, and Alloy 20) are susceptible to solidification cracking (also called hot-short cracking) during slow cooling.

Recommended interpass temperature limits are summarized in Figure 600-22 for common pressure vessel materials. Note that the recommended lower limits exceed the ASME Code minimum preheat temperatures for some materials. See Section 100, 300, and Appendix A of the Welding Manual for other materials or for additional information on interpass temperature control.

Preheat and Interpass Temperature Recommendations for Common Pressure Vessel Materials

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