Thermal Stress and Glass-Lined Equipment
Like thermal shock, thermal stress is caused by subjecting glass to temperature differential over a short period of time. Stress occurs at areas of high glass concentration, such as at connecting welds between the vessel shell and jacket (at the top and bottom jacket closure and rings), and at welds between the vessel shell and half-pipe coil jacket. Excessive temperature differentials create unusually high stresses at these areas and cause the glass to crack. Glasslined equipment that sustains thermal stress damage usually must be reglassed.
Circumstances of thermal stress:
• Noncirculating water or condensation that freezes in the vessel jacket
• Rainwater that freezes inside the baffle
• Improperly performed maintenance
Consider the Maximum Temperature Differential Rule. Prevent damage by observing the rule. Do not expose glass-lined equipment to a temperature differential greater than 260° F.
Thermal stress looks very different from thermal shock damage. It can appear as a crack that follows around the entire circumference of a vessel along a weld seam. The crack extends to the vessel steel.
