An examination surface morphology and in situ studies of metal

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
84
AN EXAMINATION SURFACE MORPHOLOGY AND IN SITU
STUDIES OF METAL DUSTING LEADS TO EXTERNAL PITS ON
ASTM A 516 GR 60 STEAM COIL OF WATER SEAL DRUM EXPOSED
TO FLARE GAS IN MTBE PLANT
1
A.C.Mariappan*, 2
K.Krishnamoorthy & 3
S.Mareeswaran
1
Asst. Professor, Department of Marine Engg., PSN College of Engineering & Technology
2
Research Scholar, Anna University, Chennai,
3
Research Scholar, Anna University, Chennai.
A B S T R A C T
Metal dusting or catastrophic carburization is venomous form of high temperature
corrosion begins with carbon deposition on the metal surface followed by diffusion of surface
carbon into the metal which eventually causes superficial deposition of carbon on the metal
and kept prolonged for 720 hrs at temperatures in the range, 450o
C -1100o
C in carbon-
supersaturated2
(carbon activity > 1) environments having relatively low oxygen partial
pressures. Experiments have been carried out in thermo gravimetric analysis evaluation. A
screening process was conducted at two different materials with various alloy composition to
choose for further investigation. Two test coupons were taken for experimental analysis
among one of them ASTM A516 Gr60 carbon steel and another one is Chromium based
carbon steel and both were exposed on the flare line testing locations found with metal
degradation varied in both cases. It was found that the poorer the alloy composition, the
higher the carbon formation rate. The presence of methanol increased the carbon formation
rate significantly but the methanol content did not however seem to be decisive for the carbon
formation rate. Field experiments were also carried out by the means of determining limits
for carbon free operation.
Key Words: MD, MTBE, CC, TGA, ASTM A516 Gr60, TML & Corrosion Coupon
Locations, SG, FG, HC, NG, SMR
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 4, May – June 2013, pp. 84-95
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85
INTRODUCTION
Metal Dusting (MD) is one form of metal degradation due to the resulting of
carburization resulting in accelerated localized pitting which occurs in carburizing gases and
or process stream containing carbon and hydrogen. Pits usually form on the superficially and
may contain soot or graphite dust. Metal dusting or catastrophic carburization1
(CC) is
venomous form of high temperature corrosion begins with carbon deposition on the metal
surface followed by diffusion of surface carbon into the metal which eventually causes
superficial deposition of carbon on the metal and kept prolonged for 360 hrs at temperatures
in the range, 450o
C -1100o
C in carbon-supersaturated2
(carbon activity > 1) environments
having relatively low oxygen partial pressures. Experiments have been carried out in thermo
gravimetric analysis (TGA) equipment. A screening process was conducted of two different
materials with various alloy composition to choose for further investigation. Two test
coupons were taken for experimental analysis among one of them ASTM A516 Gr 60 carbon
steel and another one is Chromium based carbon steel and both were exposed on the flare line
testing locations (TML & Corrosion Coupon Locations) found with metal degradation varied
in both cases. It was found that the poorer the alloy composition, the higher the carbon
formation rate. The presence of methanol increased the carbon formation rate significantly
but the methanol content did not however seem to be decisive for the carbon formation rate.
Field Experiments were also carried out by the means of determining limits for carbon free
operation. Metal dusting(MD) or catastrophic carburization1
engineering alloys are
vulnerable to metal dusting when exposed to strongly carburizing environments at elevated
temperatures, whereby the alloys corrode to produce metal, metal carbide, carbon, and oxide
particles. It has also been documented that metal dusting did happen at temperatures as high
as 1100°C in heavily reducing environments. In petrochemical plants, for example, metal
dusting has been experienced in steam reforming furnaces used to manufacture synthesis
gases (e.g. H2
, CO, and CO2
). The graphite growth is caused by carbon atoms from the solid
solution attached to the graphite planes growing vertical to the alloy surface. This initiates a
localized degradation of the alloy and, as a result, metallic particles in the form of pitting are
released and transfer into the coke layer.
SYNTHESIS GAS MIXTURE: 25%CO+72%H2+3%H2O
Synthesis Gas (SG) is nothing but the combination of Hydrogen and Carbon named as
Hydro Carbon (HC). SG is the production of methanol came from coal and also terms as
Flare Gas (FG – Fig 1). Today, synthesis gas is most commonly produced from the methane
component in Natural Gas (NG), because natural gas contains hydrogen. Three processes are
commercially practiced. At moderate pressures of 4 MPa (40 atm) and high temperatures
(around 850 °C), methane reacts with steam on a nickel catalyst to produce syngas according
to the chemical equation:
CH4 + H2O → CO + 3 H2
This reaction, commonly called steam-methane reforming (SMR), is endothermic, and
the heat transfer limitations place limits on the size of and pressure in the catalytic reactors
used. Methane can also undergo partial oxidation with molecular oxygen (at atmospheric
pressure) to produce syngas, as the following equation shows:
2 CH4 + O2 → 2 CO + 4 H2

86
As described above, several gas species, for example methane or higher
hydrocarbons, are not expected or detected in significant concentrations due to slow kinetics
and were rejected in the calculations. In order to calculate carbon activities higher than unity
in the gas phase, all solid (and liquid) states of pure carbon were suspended in the TC-
modeling. The carbon activity as a function of temperature and pressures for two possible
equilibrium based on the same input composition are shown bellow. If water vapor is
excluded from the equilibrium as shown in given example, the CO2 content increases from
1.6% (in 23% CO + 2.5% H2O +73% H2) to 4.1% (in 20.4%CO +75.5%H2) at 650°C, but
the carbon activity will still be high.
Fig – 1
METHANOL
Methanol, CH3OH, (i.e. methyl alcohol) is the simplest aliphatic alcohol, and is the
first member of the homologous series. Methanol is a colorless liquid, completely miscible
with water and organic solvents and is very hydroscopic. Methanol has an agreeable odor and
a burning taste. Methanol is a potent nerve poison.
Methanol has the physical properties
• Melting Point : -97o
C
• Boiling Point : 65o
C
• Relative Density : 0.8
Methanol and it also called as wood spirits, is a chemical with the formula CH3OH (often
abbreviated Me OH). Methanol acquired the name also known as methyl alcohol, wood
alcohol and wood naphtha. "Wood alcohol" was once produced chiefly as a byproduct of the
destructive distillation of wood. Modern methanol is produced in a catalytic industrial
process directly from carbon monoxide, carbon dioxide, and hydrogen.

0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue
Other names of Methanol
Hydroxymethane
Methyl alcohol
Methyl hydrate
Methyl hydroxide
Methylic alcohol
Methylol
Wood alcohol
Methanol can catalyze the production of methanol from carbon
high selectivity (> 99.8%):
CO + 2 H2 → CH3OH
One way of dealing with the excess hydrogen is to inject carbon dioxide into the methanol
synthesis reactor, where it, too, reacts to form methanol according to the equation:
CO2 + 3 H2 → CH3OH + H2O
Some chemists believe that the certain catalysts synthesize methanol using CO
intermediary, and consuming CO only indirectly.
CO2 + 3 H2 → CH3OH + H2O
Where the H2O byproduct is recycled via the water
CO + H2O → CO2 + H2,
This gives an overall reaction, which is the same as listed above.
CO + 2 H2 → CH3OH
Stochiometric adjustment
Stochiometric for methanol production requires the ratio of H
partial oxidation process yields a ratio of 2, and the
3. The H2 / CO ratio can be adjusted to some extent by the water
CO + H2O → CO2 + H2,
It provides the appropriate stochiometric for
Toxicity
Methanol has a high toxicity in humans.
6499(Online) Volume 4, Issue 4, May – June (2013)
87
Methanol can catalyze the production of methanol from carbon monoxide and hydrogen with
Some chemists believe that the certain catalysts synthesize methanol using CO
intermediary, and consuming CO only indirectly.
O byproduct is recycled via the water-gas shift reaction
This gives an overall reaction, which is the same as listed above.
Stochiometric for methanol production requires the ratio of H2 / CO to equal 2. The
process yields a ratio of 2, and the steam reforming process yields a ratio of
/ CO ratio can be adjusted to some extent by the water-gas shift reaction,
the appropriate stochiometric for methanol synthesis.
Methanol has a high toxicity in humans.
June (2013), © IAEME
monoxide and hydrogen with
Some chemists believe that the certain catalysts synthesize methanol using CO2 as an
/ CO to equal 2. The
process yields a ratio of
gas shift reaction,

88
Thermodynamic properties of Methanol
Phase behavior
Triple point 175.5 K (−97.7 °C), Pa
Critical point 513 K (240 °C), 78.5 bar
Std enthalpy change
of fusion, ∆fusHo 3.1773 kJ/mol
Std entropy change
of fusion, ∆fusSo 18.1 J/(mol·K)
Std enthalpy change
of vaporization, ∆vapHo +35.278 kJ/mol
Std entropy change
of vaporization, ∆vapSo 113 J/(mol·K)
Gas properties
Std enthalpy change
of formation, ∆fHo
gas
-201.3 kJ/mol
Standard molar
entropy,
So
gas
239.9 J/(mol K)
Heat capacity, cp 52.29 J/(mol K) at 77°C
61.43 J/(mol K) at 100-
223°C
Heat capacity ratio,
γ = cp/Cv
1.203 at 77°C
van der Waals'
constants
a = 964.9 L2
kPa/mol2
b = 0.06702 liter per mole
FLARE STACK / FLARE HEADERS
The released waste gases and liquids are routed through a large piping system placed
vertically called as flare headers. The released gases are burned as they exit the flare stack’s
tip Fig - 3. The size, color and brightness of flame gives the resulting the flammable
material's flow rate in terms of joules per hour (or Btu per hour). Most industrial plant flares
have a vapor-liquid separator Fig – 2 (also known as a knockout drum) upstream of the flare
to remove any large amounts of liquid that may accompany the relieved gases. Steam is very
often injected into the flame to reduce the formation of black smoke. In order to keep the
flare system functional, a small amount of gas is continuously burned, like a pilot light, so
that the system is always ready for its primary purpose as an over-pressure safety system.

89
Fig - 2
Some sources consider that flaring constitutes a hazard to human health and a contributor to
the worldwide anthropogenic emissions of carbon dioxide. For example, oil refinery flare
stacks may emit methane and other volatile organic compounds as well as sulfur dioxide and
other sulfur compounds, and toxics ... all of which are known to exacerbate asthma and other
respiratory problems. As another example, flaring at oil and gas production sites may emit
methane, sulfur dioxide, aromatic hydrocarbons (benzene, toluene and xylenes), as well as
carcinogens such as benzapyrene.
Fig - 3
The adjacent flow diagram depicts the typical components of an overall industrial flare
stack system:
A knockout drums to remove any oil and/or water from the relieved gases.
A water seal drum to prevent any flashback of the flame from the top of the flare
stack.
As alternative gas recovery system for use during partial plant startups and/or
shutdowns as well as other times when required. The recovered gas is routed into the fuel gas
system of the overall industrial plant.
A steam injection system to provide an external momentum force used for efficient
mixing of air with the relieved gas, which promotes smokeless burning.

90
A pilot flame (with its ignition system) that burns all the time so that it is available to
ignite relieved gases whenever needed.
The flare stack, including a flashback prevention section at the upper part of the flare
stack.
ASTM A516 Gr 60
A consistent description of metal dusting on ASTM A516 Gr 60 iron is proposed for
the field experiment and its related details are given in Table 1, 2 & 3:
Chemical Composition of ASTM A516 Grade 60
Composition Percentage % Composition Percentage %
C 0.2 Cu 0.3
Si 0.4 Ni 0.3
Mn 0.5/1.40 Mo 0.08
P 0.03 Nb 0.01
S 0.03 Ti 0.03
Al 0.02 V 0.02
Cr 0.3
Table 1 Typical Chemical Composition of ASTM A516 Grade 60 / ASME SA516 Grade 60
Table 2 Typical Mechanical Values of ASTM A516 Grade 60 /
ASME SA516 Grade 60
Standard Description
ASTM/ASME A/SA516 - Grade 60
DIN Standard DIN 17155 HII
British Standard BS1501-161-430A
European Norm EN10028 P265GH
Table 3 Equivalent Specifications and Standards of ASTM A516 Grade 60 /
ASME SA516 Grade 60
DUCTILE TO BRITTLE TRANSITION
Notched bar impact testing of a specimen over a temperature range will show a
change from ductile fracture at higher temperatures to brittle fracture at lower temperatures
revealed by a drop in impact energy. This testing raises the important issues concerning the
fracture toughness of steel which can change dramatically over a relatively small temperature
range. Consideration should therefore be taken when using steel in particular working
environments, especially ones where significant temperature variation is commonplace.
Properties Value
Tensile strength (N/mm2
) 410/530
Yield stress/ min (N/mm2
) 265

91
Sequential metal degradation was carried out in the following Oder:
a) Cementite formation on the ferrite surface.
b) Graphite formation on the Cementite layer.
c) As the graphite layer grows thicker and tighter the carbon activity drops to unity and Cementite
starts to decompose, I .e. Type I mechanism.
d) The eutectoid reaction may be fast enough to form an intermediate eutectoid layer;
Cementite → Ferrite + Graphite.
e) No more Cementite forms in contact with graphite in the coke, i.e. the steady state process
have started the Type II mechanism.

92
CHROME MOLYBDENUM PIPE / PLATE
Chrome Molybdenum steel plate / Pipe (often referred to in the industry as Chrome Moly) is
used for a wide variety of applications particularly in the oil and gas industry, the nuclear
industry and fossil fuel power stations. The molybdenum provides increased strength and
higher working temperatures whilst the chromium facilitates excellent corrosion resistance
and oxidation. Chrome Moly pipe has become a standard in the power generation industry
and the petro-chemical industry, not only because of its tensile strength, corrosion resistance
and high-temperature strength, but also for its cost-effectiveness. Grades P-11 & P-22 are
prevalent grades for the power industry, while P-5 & P-9 are the major refinery processing
grades utilized.
Sizes:
1/4” Nominal to 24”O.D. Seamless Pipe
Wall Thickness – Schedule 40 through XXH
Chrome Moly Pipe Specifications & Grades
SA335 & A335 – Grades P5, P9, P11,
A691 1-1/4 Chrome through 9 Chrome (Welded Alternative to A335)

93
Heat Treatment Requirements for Ni / Cr Metals:
It was shown that the metal dusting process is characterized:
(i) By a serrated appearance of the interface between graphite and the outer layer of the
substrate, which is the instable carbide Fe3C in the case of iron and the metal phase in the
case of nickel,
(ii) (ii) By the perpendicular orientation of the intrusions of graphite to the original
surface of the substrate in the case of chromium. Hence, it can be supposed that the free ends
of the growing graphite lattice planes act as active centers for disintegration.
CONCLUSION
In high Cr ferritic steels, the Cr diffusion rate is about one order of magnitude larger
than in austenitic steels. Ferritic Fe-20Cr steel is fully protected by a surface oxide film,
while the austenitic 304 stainless steel undergoes metal dusting. The importance of rapid Cr
diffusion is further discussed along with findings on the effects of surface finish.
Due to development of advanced catalysts and efforts to increase the efficiency of
processes involving the production of syngas, metal dusting corrosion has become more
prevalent. Failures of iron-base alloys as well as nickel-base alloys which contain insufficient
scale-forming elements have prompted equipment designers to seek materials that are more
resistant to metal dusting. Field and laboratory data confirm the desirability of addition of
Element P-5 P-9 P-11 P-22
K41545 S50400 K11597 K21590
Carbon 0.15 max 0.15 max 0.05 - 0.15 0.05 - 0.15
Manganese 0.30 - 0.60 0.30 - 0.60 0.30 - 0.60 0.30 - 0.60
Phosphorous,
max
0.025 0.025 0.025 0.025
Sulfur, max 0.025 0.025 0.025 0.025
Silicon 0.50 max 0.25 - 1.00 0.50 - 1.00 0.50 max
Chromium 4.00 - 6.00 8.00 - 10.00 1.00 - 1.50 1.90 - 2.60
Molybdenum 0.45 -0.65 0.90 - 1.10 0.44 - 0.65 0.87 - 1.13
P-5 P-9 P-11 P-22
Tensile Strength,
min., psi
ksi 60 60 60 60
MPa 415 415 415 415
Yield Strength, min.,
psi
ksi 30 30 30 30
MPa 205 205 205 205

94
certain scale-forming and carbide-forming elements in conjunction with a nickel-base alloy
matrix to limit pit progression rates.
All engineering alloys based on Fe, Ni, Co, even those alloyed with Cr, Al and Si, are
more or less susceptible to metal dusting, although the incubation time may differ. When a
metal dusting pit starts to grow, the kinetics is catastrophic at least from an engineering point
of view. A solution to the metal dusting problem may be found in new alloy systems free
from carbide formers, such as Fe and Cr, and free from graphite formers, such as Ni and Co.
The best performer overall in the laboratory test was alloy 693, which possesses very high
chromium and aluminum contents. In-situ field exposures in syngas environments have
confirmed this alloy's superior performance.
Metal dusting prevention
♣ Adjustment or careful selection of process parameters (T, P, C)
♣ Development of new, metal dusting resistant, alloys
♣ Application of coatings to protect the underlying metal/alloy matrix (Cr- surface
oxide layer)
♣ Mixing process gas with low concentration of sulfur compounds (H2S, CS2, (CH3)2S2,
etc.)
♣ Dense Cr-containing oxide is more protective Pre-polished samples treated in H2O/Ar
at the lowest temperature appear to have the best resistance
Chromium based carbon steel and both were exposed on the flare line testing
locations found with metal degradation varied in both cases. It was found that the poorer the
alloy composition, the higher the carbon formation rate. The presence of methanol increased
the carbon formation rate significantly but the methanol content did not however seem to be
decisive for the carbon formation rate. Experiments were also carried out by the means of
determining limits for carbon free operation.
REFERENCE
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[4]. J. Pattinson,” On carbon and other deposits from the gases of blast furnaces in
Cleveland”, J. Iron Institute, No 1, London, pp. 85-100 (1876).

95
[5]. E. Camp, C. Phillips, L. Gross, “Corrosion of 18-8 Alloy furnace tubes in high
temperature vapour Phase cracking service”, Corr., Vol. 1, p.149-160 (1945).
[6]. H.J.Grabke, Metal dusting, Material and Corrosion, 2003, 54, pp. 736-746.
[7]. “Handbook of Case Histories in Failure Analysis,” Esaklul, K. A., ed., ASM, 1992, pp
351-353.
[8]. Private Communications, Special Metals, December, 1997.
[9]. S.Strauss and H.J.Grabke, Materials and Corrosion, 49, 1998, pp 321-327.
[10]. D. B. Roach, “Carburization of Heat-Resistant Alloys”, Paper No 7, Corr., NACE
(1976).
[11]. Doi, T.; Kitamura, K.; Nishiyama, Y., et al.: Surf. Interface Anal. 40, 1374 (2008).
[12]. Eberle, F.; Wylie, R.D.: Corrosion 15, (12), 622t (1959).
[13]. Baker, B.A.; Smith, G.D.; Hartmann, V.W.; Shoemaker, L.E.: “Nickel-base material
solutions to metal dusting problems”. CORROSION /2002 (Houston, TX, NACE,
2002) (Paper No.2394).
[14]. E. Pippel, J. Woltersdorf and R. Schneider, Materials and Corrosion, 49 309 (1998).
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