Weldments in materials with a Carbon Equivalent (CE) >= 0.5 should be exposed to a hydrogen bake out upon completion of welding. The following formula should be used to determine Carbon Equivalent.
CE = C + (Mn/6) + [(Cr + Mo +V)/5] + [(Ni + Cu)/15]
The part should not be allowed to cool to less than 100°C (212°F) or the preheat temperature (whichever is greater) between completion of welding and the start of the hydrogen bake out procedure.
The bake out temperature should, as a minimum, be no less than 200°C (392°F) and, as a maximum, be equal to the maximum interpass temperature.
The bake out time should not be less than one hour per inch of weld cross-section and not less than one hour total.
The bake out procedure may be waived if the part goes directly from weld completion to PWHT before the part has time to cool below the minimum preheat temperature.