May 2008

Engineering Case Histories

Case 44: Cracking due to sudden temperature changes in piping

Excessive thermal stresses can be the cause

Sofronas, A., Consulting Engineer

Shallow cracking was observed during inspection of a valve spool piece used to flash a cold liquid. The part was scrapped and replaced in kind. Unfortunately, no metallurgical analysis was performed. The spool was made of A106 steel and had seen five years of service. The valve cycled and flashed a liquid to –40°F once per minute. Fig. 1 shows the spool was steam-jacketed (red) in the location where cracking occurred. The bore (blue) was at a temperature of –40°F. It was suggested that cold vapor contacting the hot surface had caused the cracking and this analysis was performed to determine the stresses.

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