Failure Analysis Case History No. 011

Industry: Gas Treating
Specimen Description: 6" Furnace Tube
Material: Carbon Steel
Environment: Rich Oil containing C1-3 paraffin hydrocarbons
Background:
Horizontal, carbon steel furnace tubes in a Rich Oil Fractionator furnace failed causing a fire.
Time in Service: 30 years
Findings:
Laboratory analysis showed that the carbon steel tube sample had experienced long term overheating under a heavy coke layer. I.D. pitting was observed under the coke. The pits were believed to be due to metal dusting, based on a dark etching, carburized layer below the pits. Observation of the microstructure showed that the dark etching layer was100% pearlite. The undegraded pearlite proved that metal temperatures had exceeded the AC3 transformation temperature at some time. Long term metal temperatures were estimated at approximately 1000F, based on the presence of graphite nodules in the completely decarburized ferrite matrix.

 

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