Inspectioneering Journal

99 Diseases of Pressure Equipment: Thermal Shock

By John Reynolds, Principal Consultant at Intertek. This article appears in the July/August 2003 issue of Inspectioneering Journal.

Thermal shock is another one of those pressure equipment afflictions where communication with operating groups is a vital factor in prevention. Thermal shock failures usually involve sudden quenching of high temperature equipment and furnace tubes with a relatively cooler liquid or saturated steam containing some liquid, but not always. It can occur from sudden cooling of any high temperature equipment, or sudden cooling of even lower temperature equipment that causes it to suddenly be operating in a range in which it is now brittle. Physical restraint of equipment that needs to grow as it's temperature increases or contract as its temperature decreases, will often produce deformation or cracking failures. Valve body cracking of regen valves in Cat Reforming units is a good example of thermal shock that results in that common "mud flat" cracking appearance on the ID of the valves. Blowing dust or particulates off from convection section tubes with high pressure steam or water sprays is another example of how to produce thermal shock cracking on furnace tubes.

The best way of avoiding unexpected thermal shock is to make sure that operations and process engineers understand what can happen to equipment (or perhaps to them personally) if they suddenly chill it. It was a thermal shock that not too long ago caused a heat exchanger in a gas plant in Victoria, Australia to crack open brittlely while in service, causing two fatalities and an enormous economic impact.

Do all your operators know about the potential for and the effects of thermal shock and what they need to do in order to avoid it?

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