Coke deposition on and removal from metals and heat-resistant alloys under steam-cracking conditions

P. R. S. Jackson; D. J. Young; D. L. Trimm

doi:10.1007/bf01106559

Damage Characterization of Heat Resistant Steels After Long Service in Reforming Plants

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2016-63555 ◽

2016 ◽

Author(s):

Antonello Alvino ◽

Alessandra Antonini ◽

Daniela Lega ◽

Canio Mennuti ◽

Andrea Tonti

Keyword(s):

Corrosion Resistance ◽

Chemical Composition ◽

Creep Damage ◽

Mechanical Tests ◽

Coke Deposition ◽

Process Conditions ◽

Secondary Phases ◽

Heat Resistant ◽

Damage Characterization

ASTM A 297 grade HP steels are widely employed for radiant tubes in reforming furnaces: this class of heat resistant alloys shows high creep and corrosion resistance, ensuring good performances in extreme pressure and temperature conditions. The typical microstructure of such materials is an austenitic matrix surrounded by a network of interdendritic carbides, which contain chromium and other carbide forming elements, namely Nb, Ti, W, Zr and Y. During long service life, these high strength materials may suffer aging or even severe damage, especially when process conditions allow coke deposition, or maintenance procedures are not carried properly. Service aging can be summarized, for HP steels, in terms of microstructure degradation: coalescence and coarsening of interdendritic precipitates, precipitation of secondary carbides in the austenite matrix and transformation of niobium-rich carbides in the G-phase silicide are the typical phenomena occurring on the microstructure of these alloys during service. Carburization can also occur in radiant tubes, since their inner wall side is exposed to hydrocarbon-rich process fluids: carbon diffuses into the metal matrix, causing massive precipitation of chromium-rich carbides. The alloy corrosion resistance is then reduced, resulting in surface attack, cracks development and a general wastage of the material. Furthermore, the high temperatures, which tubes are exposed to, can also induce creep, especially if a local tube overheating occurs: cavities and microcracks, mainly localized at precipitates, are the typical evidences of creep damage on HP steels. The present work is aimed on the damage characterization of several radiant tubes in HP alloys, after long term service aging in reforming plants. We employed optical and electron microscopy, EDX elements mapping and mechanical tests, in order to characterize and evaluate the various damages affecting the alloys. Microstructure evolution has been detected in all the analyzed tubes, but we found that such a phenomenon was strictly influenced by the chemical composition of each alloy, so that in presence of small amounts of titanium and tungsten, the chemical evolution of the secondary phases was appreciably contained. Creep also was observed in all the investigated tubes and its extent was found to be related to both alloy composition and process conditions. These latter have assumed to be the main driving factor for carburization, since we observed that slight differences in temperature, pressure, chemical composition of the process fluid and tube maintenance dramatically conditioned the performances of each tube. Massive precipitation and material degradation, in fact, were found in some cases, but, on the other side, no appreciable evidence of carburization damage was observed on other cases.

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An empirical investigation of the influence of sulfur additives on the catalytic rate of coke deposition and CO formation in the steam cracking of LPG over Incoloy 600 and stainless steel

Chemical Engineering Journal ◽

10.1016/j.cej.2013.09.111 ◽

2014 ◽

Vol 238 ◽

pp. 210-218 ◽

Cited By ~ 13

Author(s):

Nazi Rahimi ◽

Ramin Karimzadeh ◽

Seyed Mahdi Jazayeri ◽

Kamran Danaie Nia

Keyword(s):

Stainless Steel ◽

Empirical Investigation ◽

Coke Deposition ◽

Steam Cracking ◽

Catalytic Rate

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Coke deposition under steam cracking conditions - Study of the influence of the feedstock conversion by micropilots experiments

Materials and Corrosion ◽

10.1002/(sici)1521-4176(199805)49:5<360::aid-maco360>3.0.co;2-d ◽

1998 ◽

Vol 49 (5) ◽

pp. 360-366 ◽

Cited By ~ 7

Author(s):

J. Browne ◽

P. Broutin ◽

F. Ropital

Keyword(s):

Coke Deposition ◽

Steam Cracking

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Coke Formation Reduction in the Steam Cracking of Naphtha on Industrial Alloy Steels Using Sulfur-Based Inhibitors

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2304 ◽

2010 ◽

Vol 8 (1) ◽

Cited By ~ 6

Author(s):

Darioush Salari ◽

Aligholi Niaei ◽

Mohammad Reza Shoja ◽

Reza Nabavi

Keyword(s):

Coke Formation ◽

Dimethyl Disulfide ◽

Coke Deposition ◽

X Ray ◽

Industrial Alloy ◽

Stainless Steel 304 ◽

Steam Cracking ◽

Alloy Steels ◽

Cylindrical Reactor ◽

Scanning Electron

Coke formation reduction during naphtha pyrolysis was investigated using dimethyl disulfide (DMDS) and carbon disulfide (CS2) as inhibitors with different feed stocks. Different industrial nickel alloy steels such as stainless steel 304 and 316 (SS304, SS316), HP-modified (HP-mod) and HP-micro (HP-mic) were used as coupons in a quartz cylindrical reactor for coke formation studies. Coke formation significantly reduced in the presence of the additives or using feeds with more sulfur compounds. It was revealed that HP-mic alloy has the least coke deposition rate between other alloys. Scanning electron microscope (SEM) and energy dispersive X-ray analyzer (EDAX) were used for morphological and elemental surface analyses, respectively. It was found that cokes formed in presence of sulfurous inhibitors are softer and have less metal concentrations.

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