Premium
Metal dusting in CCR platforming unit
Author(s) -
Dampc J.,
Grzesik Z.,
Hucińska J.
Publication year - 2009
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200805026
Subject(s) - materials science , carbide , metallurgy , chromium , molybdenum , scanning electron microscope , carburizing , alloy , graphite , corrosion , tube furnace , composite material , chemical engineering , engineering
The mechanism of metal dusting of 9Cr‐1Mo steel in CCR platforming unit, based on examinations of a charge heater tube, is presented. The tube operated for 10 years, and the metal skin temperature was about 600 °C. The feed was composed of hydrotreated naphtha and hydrogen gas. The mechanism of the corrosion was elucidated using scanning electron microscopy, electron probe microanalysis and X‐ray diffraction technique. It has been found that the carbon deposition on the steel surface and its inward diffusion into the steel is accompanied by the outward diffusion of carbide forming elements, i.e. chromium and molybdenum. At an advanced stage of the metal dusting process a thin layer of fine chromium‐rich carbides beneath the steel surface exists. The layer is followed by a porous zone composed of big degraded primary carbides and fine carbides instead of alloy ferrite, with chromium and molybdenum content higher than the ferrite inside the tube wall. On the steel surface, a layer of coke composed of graphite, iron and M 7 C 3 carbides is formed and the uniform wastage of the steel takes place. Possible influence of some sulphur additions to the CCR platformer feed during the future service on degradation of the subsurface material has been considered.