Temper Embrittlement Thermal Aging
Low-alloy Cr – Mo steels are susceptible to temper embrittlement after long time operation at temperatures above approximately 700°F, which can result in severely reduced CV-impact toughness at temperatures up to 250°F or higher. Brittle fracture is prevented by restricting startup and shutdown procedures to limit the pressure to 20% of the design pressure at temperatures below 250°F.
Temper embrittlement cannot be detected by any nondestructive examination technique. The severity of temper embrittlement that has occurred can be determined by removing “boat” samples from plates and weldments for CV-impact testing. However, this method would necessitate repair of the vessel and should only be performed after consultation with pressure vessel and materials engineers.
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