Overheating

Main Member Type: Rolled Beam (occasionally plate girder)
Attached Member/ Detail Type: N/A
Error Type: Not Monitoring Temperature
Description of Error: Heating with oxy-fuel torch to camber, curve or straighten a member,
but not monitoring the temperature with thermal crayons or electronic sensors.
QA Inspector suspects material was overheated (over 1200 F/650 C for low alloy,
1100 F/ 600 C for Q & T) based on observation of bright red color during heating,
local distortion/melting of base metal and mill scale, or temper colors on steel surface.
Overheating may reduce ductility and toughness, initiate or propagate discontinuities,
cause local distortion and high residual stresses,
and adversely effect material properties of quenched and tempered steel.
Solution Recommended: IOverheating may cause irreversible effects, so "repair" may not be possible
without material replacement. Physical properties of heated areas must be assessed to determine
if material is still acceptable for incorporation in structure. Possible indicators include hardness checks
(Brinell, Knoop, Vickers or Rockwell) which can be down in-situ, or yield,
ductility and Charpy V-notch tests which require removing material for specimens.
Metallographic analysis can determine if microstructure has change,
but this is very sophisticated and site-specific for this situation.
Tests should be conducted by a qualified testing agency at the fabricator's expense.
If hardness testing provides adequate assurance, the material bay then be accepted.
Otherwise, either the material must be completely replaced or an adequate number of specimens
extracted and tested to verify properties. It tests are acceptable, the fabricator must develop
a method to replace the specimens.
Required Final Checks / Verification: If hardness testing provides adequate assurance, the material may ten be accepted. Otherwise, either the material must be completely replaced or an adequate number of specimens extracted and tested to verify properties. If tests are acceptable, the fabricator must develop a method to replace the specimens.
Was Repair Successful ?: For cases to date involving Grade 36 & 50 250 & 345) steel, Hardness tests have satisfied ILDOT without additional destructive testing.
Other Possible solutions: Replace material: extensive NDE, including wet-particle MT, through thickness and surface wave UT, and hardness testing; stress relief of heated areas (difficult, and unwanted distortion possible); or adding reinforcing plates.
Remarks: For most mild steels (nominal yield £50 ksi / 345 mPa), heat not exceeding transition temperature (1600 F /870 C) and cooling in air without quenching probably results in minimal adverse changes to properties. However, must have some verification.

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