Performance of chromia- and alumina-forming Fe- and Ni-base alloys exposed to metal dusting environments: The effect of water vapor and temperature

doi:10.1016/j.corsci.2014.11.022

Corrosion Science

Volume 92, March 2015, Pages 58-68

https://doi.org/10.1016/j.corsci.2014.11.022 Get rights and content

Highlights

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The decrease in temperature increased the attack by metal dusting.
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At 1 atm, the replacement of H₂ by H₂O led to a decrease in metal dusting attack.
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Despite high total pressures, the addition of H₂O decreased metal dusting attack.

Abstract

Fe- and Ni-base alloys including an alumina-forming austenitic alloy were exposed for 500 h under metal dusting environments with varying temperature, gas composition and total pressure. For one H₂–CO–CO₂–H₂O environment, the increase in temperature from 550 to 750 °C generally decreased metal dusting. When H₂O was added to a H₂–CO–CO₂ environment at 650 °C, the metal dusting attack was reduced. Even after 5000 h at a total pressure of 9.1 atm with 20%H₂O, the higher alloyed specimens retained a thin protective oxide. For gas mixtures containing little or no H₂O, the Fe-base alloys were less resistant to metal dusting than Ni-base alloys.

Introduction

Metal dusting is a catastrophic form of corrosion occurring between 400 and 800 °C in environments for which the carbon activity (a_c) is greater than 1. It leads to the disintegration of metallic materials as a result of the formation of a carbon deposit containing metallic particles, carbides and oxides. A large number of studies have been devoted to define which alloys and compositions [1], [2], [3], [4], [5], [6], [7], [8] are more resistant to metal dusting. The influence of alloy grain size [3], [9], surface finish, cold working [3], [9], [10], [11], [12] or the addition of a coating [13], [14], [15], [16] on the resistance to such corrosion has been evaluated. Other studies were interested in the effect of parameters defining the metal dusting environment: temperature [12], [17], total pressure [11], [17], [18], [19] or gas composition [19], [20], [21], [22], [23].

Quantifying degradation by metal dusting is complex because there is no single gas mixture, temperature and total pressure encountered in industrial applications. Those parameters differ with the application and process, which results in a wide range of laboratory studies and difficulties comparing experimental results. One relevant observation about laboratory studies is that typical gas compositions creating a metal dusting environment contain little or no water vapor, in general <10% and very few contain ⩾20% of H₂O. However, Hoffman et al. [24] reported that industrial applications can contain up to 40% H₂O, in addition to being run at a high total pressure. These differences between laboratory and industrial conditions appeared to be significant as laboratory studies tend to highlight the superiority of Ni-base alloys, as shown by Grabke et al. [25], while Hoffman et al. [24] reported better resistance for Fe-base alloys under industrial conditions.

This study surveyed the influence on metal dusting of temperature as well as H₂O content and total pressure (expanding initial results published previously [26], [27]). Three sets of tests were defined. The first one was carried out at atmospheric pressure in a given CO₂–CO–H₂–H₂O mixture with the temperature being raised from 550 to 750 °C. The second one was carried out at 650 °C and atmospheric pressure in a CO₂–CO–H₂ environment in which H₂ was replaced by H₂O, leading to a decrease in a_c. The third one was also performed at 650 °C under the same CO₂–CO–H₂ environment in which H₂O was added from 0 to 28% by keeping the CO/CO₂ and CO/H₂ ratios constant and raising the total pressure to keep a_c constant. Under each metal dusting environment, a wide range of commercial chromia- and alumina-forming Fe- and Ni-base alloys were tested. The test matrix also included a new class of alumina-forming austenitic (AFA) stainless steels, alloys developed at Oak Ridge National Laboratory to offer both good oxidation and creep resistance [28], [29], [30]. Select alloys were also oxidized at 650 °C in wet air to compare the effect of water vapor in high and low oxygen partial pressures.

Section snippets

Materials

A series of chromia- and alumina-forming Fe- and Ni-base alloys was studied under metal dusting conditions. Their chemical composition is given in atomic percent in Table 1. The alloy specimens were rectangular coupons (typically ≈ 1.5 × 10 × 19 mm), except for 3 mm thick H224 specimens, or 16 mm diameter disks for cast FeCrAlY and NiAl. A hole was drilled close to one end to facilitate their positioning within the rig. Samples were ground to a 600 grit finish with SiC paper on all faces and then cleaned

Effect of the temperature

The mass changes from Tests 1–3 at 550–750 °C are reported in Fig. 2. At 550 °C with the highest a_c, all of the Fe-base alloys lost mass (347H was not included), and three Ni-base alloys (601, H224, NiAl) exhibited mass losses. The largest mass losses were encountered for T122 and 800H alloys, which exhibited the largest visual surface degradation, while some degradation around the hole was responsible for the mass loss of the AFA alloy. The mass loss of H224 alloy was associated with the

Effect of the temperature

The decrease in metal dusting degradation observed with the increase in the temperature from 550 to 750 °C is consistent with the decrease in the equilibrium constant of the synthesis gas reaction [32], leading to a decrease in a_c, Table 2. This is also in agreement with the works of Grabke and Müller-Lorenz [3], who proposed that a temperature below 600 °C favors metal dusting and the study of Chun et al. [36] who observed a maximum metal dusting rate at 575 °C for iron exposed to a 50%CO–50%H₂

Conclusions

A series of chromia- and alumina-forming Fe- and Ni-base alloys were exposed under nine different metal dusting and one air + H₂O environments. For a given gas mixture composition, increasing the temperature from 550 to 750 °C at atmospheric pressure reduced the a_c, leading to reduced metal dusting attack, as expected. At 650 °C and atmospheric pressure, the replacement of H₂ by H₂O in a CO–H₂–CO₂ environment also reduced a_c and led to reduced alloy degradation. At 650 °C, the addition of H₂O to a

Acknowledgments

The authors are grateful to J.R. Keiser for guidance on the experimental plan and procedures. T.M. Lowe, G.W. Garner, M. Howell, H. Longmire and T. Jordan assisted with the experimental work. The research was sponsored by the United States Dept. of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.

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Performance of chromia- and alumina-forming Fe- and Ni-base alloys exposed to metal dusting environments: The effect of water vapor and temperature

Highlights

Abstract

Introduction

Section snippets

Materials

Effect of the temperature

Effect of the temperature

Conclusions

Acknowledgments

Corros. Sci.

Corros. Sci.

Corros. Sci.

Corros. Sci.

Scripta Mater.

Comp. Materi. Sci.

Appl. Surf. Sci.

Corros. Sci.

Corros. Sci.

Resistance of 9–20%Cr-steels against metal dusting

Steel Res.

Role of alloying elements in steels on metal dusting

Mater. Corros.

Protection of high alloy steels against metal dusting by oxide scales

Mater. Corros.

Alloying with copper to reduce metal dusting of nickel

Mater. Corros.

Coking and dusting of Fe–Ni alloys in CO–H2–H2O gas mixtures

Oxid. Met.

Metal dusting of nickel–aluminium alloys

Oxid. Met.

Effects of grain size, cold working, and surface finish on the metal-dusting resistance of steels

Oxid. Met.

Metald dusting resistance of steels

Mater. Sci. For.

Metal dusting of 9–20%Cr steels in increased pressure environments at 560 °C

Mater. Corros.

Metal dusting corrosion of austenitic 304 stainless steel

J. Electrochem. Soc.

Protective behaviour of newly developed coatings against metal dusting

Mater. Corros.

Metal dusting protective coatings. A literature review

Oxid. Met.

Metal dusting behaviour of alloy 800H in laboratory carbonaceous environments under high pressure

Mater. Sci. For.

Metal dusting of type 316 stainless steel in high pressure environments between 450 °C and 650 °C

Mater. Corros.

Development of Materials Resistant to Metal Dusting Degradation, Technical Report ANL-06/14

Effect of syngas composition on metal dusting of alloy 800H in simulated reforming gas atmospheres

Corrosion

Coking and dusting of Fe–Ni alloys in CO–H₂–H₂O gas mixtures