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This report presents the results of tests conducted on 554 specimens of carbon and carbon-molybdenum steel removed from petroleum refining equipment and examined for evidences of graphitization. Graphite formations were found in 33.8 per cent of these specimens.

It has been established that some steels have a greater tendency to graphitize than others; and that high aluminum content (in excess of 0.015 per cent), high operating temperatures, and the steel-making process used in meeting certain specifications are factors which affect graphitization. Of the steels examined, ASTM A I06 pipe indicated the highest tendency to graphitize; and, of the carbon steels, ASTMA 285 plate material indicated the highest resistance to graphitization. Connected nodules of graphite were found in both carbon and carbon-molybdenum steels. Although the carbon-molybdenum steel graphitized less frequently than the carbon steel, when it did graphitize, graphitization was of the more serious type.

At a temperature of 1025F accelerated laboratory tests were made at successive 1,000-hour periods to predict the graphitization of steel under service conditions. These tests showed that a steel which does not graphitize in service is not necessarily immune to graphitization. The tests also indicate that certain "heats" of plain-carbon steel, with a high aluminum content, resisted graphitization throughout 50,000 hours of service life, as well as after 3,000-hour accelerated test periods at a temperature of 1025F. It is not understood why some steels exhibit so little tendency to graphitize.

Furthermore, the data developed to date do not reveal any condition which would indicate that the sampled pressure equipment is unsafe for further service.

The series of stress-rupture tests now being conducted on graphitized plate may provide a more exact evaluation of the effect of graphitization on the high-temperature properties of welded steel.

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Published: 1957 Number of Pages: 50 File Size: 1 file , 2.1 MB