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Journal of Materials Science

, Volume 16, Issue 1, pp 170–188 | Cite as

A physical and chemical examination of an ethylene steam cracker coke and of the underlying pyrolysis tube

  • M. J. Bennett
  • J. B. Price
Papers

Abstract

The physical properties, chemical composition and structure of a carbonaceous deposit formed on a radiantly heated HK40 steel tube at 920 to 930° C after ~ 50 days cracking operations in naphtha-steam have been examined. The deposit consisted of two layers. The innermost (i.e. adjacent to the tube) varied in thickness from 20μm to 1.5 mm, and was formed by heterogeneous reactions catalysed by iron and nickel. Enhanced deposition was characterized by a higher concentration of entrapped chromium rich oxide particles, a principal source of catalytic species. The outer deposit layer was of uniform thickness, had a columnar radial and an axial layered structure, which together with the absence of any significant inorganic constituents, suggested an autocatalytic growth mechanism. The corrosion of the inner (pyrolysis) and the outer (hot box) surfaces of the underlying HK40 steel tube had similar features. The chromium rich outer scales were of variable thickness, due to the attack of certain grains, underlying which were zones denuded in carbon precipitates and intergranular silica formation. The major difference was carburization from beneath the decarburized zone at the inner surface. The processes of decarburization, carburization and of intergranular corrosion were interconnected. Carbon pick-up probably resulted from a crevice corrosion mechanism. A general reduction in the nitrogen level through the cracker tube, with enhanced denitriding at both surfaces, originated from a similar mechanism to that responsible for decarburization. The more severe denitriding at the inner surface was derived from chromium nitride conversion to the more stable chromium carbide.

Keywords

Pyrolysis Carburization Decarburization Chromium Carbide Intergranular Corrosion 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    T. B. Pierce, J. W. Mcmillan, P. F. Peck andI. G. Jones,Nucl. Instr. Methods 118 (1974) 115.Google Scholar
  2. 2.
    C. Olivier, J. W. Mcmillan andT. B. Pierce,ibid. 124 (1975) 289.Google Scholar
  3. 3.
    L. A. Zeiss andE. Heinz,Chem. Eng. Prog. 66 (1970) 68.Google Scholar
  4. 4.
    A. Fertillo andB. Princip,Hydrocarbon Processing 54 (1975) 174.Google Scholar
  5. 5.
    M. J. Bennett, M. R. Houlton, J. W. Mcmillan, C. F. Knights, R. W. M. Hawes andF. C. W. Pummery, International Conference on the Behaviour of High Temperature Alloys in Aggressive Environments, Joint Research Centre, Pettern, The Netherlands, October, 1979.Google Scholar
  6. 6.
    R. T. K. Baker, M. A. Barber, F. S. Feates, P. S. Harris andR. J. Waite,J. Catal. 26 (1972) 51.Google Scholar
  7. 7.
    R. T. K. Baker, P. S. Harris, R. B. Thomas andR. J. Waite,ibid. 30 (1973) 86.Google Scholar
  8. 8.
    T. Baird, J. R. Fryer andB. Grant,Carbon 12 (1974) 591.Google Scholar
  9. 9.
    M. J. Bennett, G. H. Chaffey, A. J. Langford andD. R. V. Silvester, UK Atomic Energy Authority Report, AERE-R7407 (1973).Google Scholar
  10. 10.
    M. J. Bennett, G. H. Chaffey, B. L. Myatt andD. R. V. Silvester, UK Atomic Energy Authority Report, AERE-R7408 (1973).Google Scholar
  11. 11.
    J. C. Bokros in “Chemistry and Physics of Carbon”, Vol. 5 edited by P. L. Walker Jr (Marcel Dekker, New York, 1969) p. 3.Google Scholar
  12. 12.
    J. Lahaye, P. Badie andJ. Ducret,Carbon 15 (1977) 87.Google Scholar
  13. 13.
    T. M. Mukhina, G. L. Stolyar, N. L. Barabanov, B. S. Borden andN. P. Solomina,Sb. tr N11 Sintetich spirtov i organ prod 5 (1974) 34.Google Scholar
  14. 14.
    H. J. Penkalla, E. Gyarmati andH. Nickel, Proceedings of the Fifth London International Carbon and Graphite Conference, September, 1978 (Society of the Chemical Industry) p. 835.Google Scholar
  15. 15.
    W. P. Hoffman, F. J. Vastola andP. L. Walker, Fourteenth Biennial Conference on Carbon, Pennsylvania State University, June 1979 (American Carbon Society) p. 139.Google Scholar

Copyright information

© Chapman and Hall Ltd 1981

Authors and Affiliations

  • M. J. Bennett
    • 1
  • J. B. Price
    • 1
  1. 1.Materials Development DivisionAERE HarwellDidcotUK

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