Thermal shock can occur when high and non-uniform thermal stresses develop over a relatively short time in a piece of equipment due to differential expansion or contraction. If the thermal expansion/contraction is restrained, the yield/tensile strength of the material can be exceeded resulting in cracks.
Thermal Shock | Materials And Corrosion Control
Damage Mechanism | Thermal Shock |
Damage Description | Thermal shock can occur when high and non-uniform thermal stresses develop over a relatively short time in a piece of equipment due to differential expansion or contraction. If the thermal expansion/contraction is restrained, the yield/tensile strength of the material can be exceeded resulting in cracks.
Thermal shock usually occurs when a colder liquid contacts a warmer metal surface such as during the rapid water cooling of high temperature locations during a fire and large temperature changes that occur from water quenching as a result of rain deluges or water dowsing. · The magnitude of the temperature differential and the coefficient of thermal expansion of the material determine the magnitude of the stress. · Fracture is related to constraint on a component that prevents the component from expanding or contracting with a change in temperature. · Cracking in cast components such as valves may initiate at casting flaws on the ID and progress through the thickness. |
Materials & Equipment | Materials
All metals and alloys. Stainless steels have higher coefficients of thermal expansion than carbon and alloy steels or nickel base alloys and are more likely to see higher stresses. Equipment · High temperature equipment in units such as FCC, cokers, catalytic reforming and hydroprocessing. Hot spot locations in refractory lined equipment · Materials that have lost ductility, such as CrMo equipment (from temper embrittlement) · Equipment subjected to accelerated cooling procedures to minimize shutdown time. · Hydrocracker hydrogen quench nozzles or mixing points · Thick sections can develop high thermal gradients |
Control Methodology | · Prevent interruptions in the flow of high temperature lines.
· Design to minimize severe restraint. · Install thermal sleeves to prevent liquid impingement on the pressure boundary components. · Design for rain or fire water deluge situations. · Review hot/cold injection points for potential thermal shock. |
Monitoring Techniques | · This type of damage is highly localized and difficult to locate. Conduct infrared surveys of suspect locations to look for temperature differentials PT and MT can be used to confirm cracking. |
Inspection Frequency | · Periodic at T&Is or immediately after thermal shock event, e.g., fire exposure, water quenching, etc. |
KPIs | · # of failures |
Reference Resources (Standards/GIs/BPs) | API RP571 (2003) |
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