Inspectioneering Journal

99 Diseases of Pressure Equipment: Graphitization

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

Graphitization is not something that operators can do much about, and thankfully it is not very common. We as engineers and inspectors have to know about this one and prevent it or detect it. It occurs when the microstructure of some carbon and low alloy steels breaks down after long exposure to elevated temperatures, like in FCCU's. The carbide phases break down in temperature ranges from 825 to 1300 F (440 - 590 C), and cause the metal to weaken and be susceptible to cracking failures. Material selection is key to avoiding graphitization failures. Metallographic analysis of coupons cut from the walls of susceptible equipment is effective in determining if graphitization may be occurring.

Have you assessed the carbon and low alloy steels in your older, higher temperature equipment to determine if they might be susceptible to graphitization cracking and failures after long periods of time in service?

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