FAILURE OF 9CR-1MO TUBES IN A FEED FURNACE OF DEHYDROGENATION UNIT

The successful uses of 9Cr-1Mo steel in boilers, superheaters and furn aces have been well established; however, the unusual failure of this material in a feed furnace of dehydrogenation unit in linear alkyl ben zene plant is reported here. Extensive experiments such as chemical co mposition examination, macro inspection, metallurgical observation, sc anning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis, together with mechanical tests, were conducted on the failed material and the results are presented. The failure described as pitt ing and cracking of the 9Cr-1Mo tubes is stated to be caused by seriou s carburization combined with hydrogen corrosion. The great stresses d eveloped by volume changes in the carburization of the metal as well a s the decomposition of the carbides are believed to be largely respons ible for the pitting and cracking of the tubes. (C) 1998 Elsevier Scie nce Limited. All rights reserved.