Direct Answer
Heat straightening uses controlled application of heat (typically 1,100–1,300°F with an oxy-fuel torch) to plastically deform and straighten a bent or distorted steel member. It is used to correct weld distortion during fabrication, to repair impact-bent members in the field, and to straighten rolled sections that arrive from the mill with excessive sweep or camber.
Full Explanation
Heat straightening works by heating a small area on the concave side of a bend, causing the heated area to yield under the restraint of the surrounding cooler metal. When it cools, the heated zone contracts and the member straightens. Multiple heating cycles may be needed for large distortions. AWS D1.1 limits maximum heat temperatures and provides guidance on approved procedures. Heat straightening should not be used for high-strength steels (A514, A709 Grade 70W) without specific engineering approval, as it can affect mechanical properties.
What This Means for Your Shop
Weld distortion is common in fabricated assemblies — particularly in welded plate girders, box columns, and members with heavy weld deposits on one side. Budget time for distortion correction in your production schedule for complex assemblies. Attempting to force distorted members into position during erection is a field safety and quality risk.
Common Mistakes
Exceeding the maximum heat temperature limit during straightening. Temperatures above 1,200°F (for A36 and A992) can cause metallurgical changes that reduce toughness, particularly in seismic applications.
Recommended Process
Use a temperature-indicating crayon or infrared thermometer to control heating temperature. For seismic members, obtain engineer approval before any heat straightening. Document heat straightening in your QC records, including member identification, temperature used, and number of cycles.