Corrosion resistant coatings for refractory lining …...Corrosion‐resistant coatings for...
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Corrosion‐resistant coatings for refractory lining anchors in aggressive high temperature environments temperature environments J.T. Bauer, M.C. Galetz, M. Schütze e‐mail: [email protected] Funded by: BMWI via AiF Period: 01.04.2012 – 31.07.2015 Motivation Motivation In a large number of technical incineration processes metallic components are in contact with aggressive gases and deposits. Especially critical are atmospheres containing halogens such as chlorine, alkalis, and heavy metal compounds, all of which cause severe corrosion damage. Aluminizing of the metallic components is a promising way to protect them. Slurry aluminizing was chosen as coating technique because it is a well established, low‐cost process even for large components. The challenge in the present project is to develop corrosion‐resistant slurry diffusion coatings in situ, directly in plants, using the process‐inherent energy for the diffusion process. The protection of refractory lining anchors is of special interest (Figs. 1 and 2), but the coating solutions for this application can also be transferred to other metallic components such as sheets or tubes. Osthövener, Kollenberg, 2007 Coating concepts for Al diffusion in aggressive environment Fig.1: Anchors for refractory linings Based on a two‐layer system of layer 1, diffusing metal (AlSi slurry) and layer2, protection of the base material and the diffusing metal from oxidation/corrosion, three coating concepts are evaluated (Fig. 3): Fig.2: Bursting of the refractory lining and corroded anchors Results – laboratory 50μm Substrate Diffusion zone Al Al Al Ge Al Glass 50μm Substrate Diffusion zone 50μm „Eutectic concept“ „Barrier concept“ „Oxygen getter concept“ Fig.5: Relationship of the cumulative probability of the surface coverage and the coating thickness; only the barrier concept leads to a homogenous diffusion coating, whereas the other coating concepts lead to a broader distribution of i ti thi k th ti th i ht Fig.3: Three coating concepts based on a two‐layer system ‐ Oxygen getter concept: Large AlSi powder particles are used for the diffusion layer, smaller Al powder particles (3‐5μm) with larger surface are used as oxygen getter Formation of Al 2 O 3 on top ‐ Eutectic concept: AlSi powder particles are used for the diffusion layer, Ge powder particles as second layer are used to form a eutectic composition with a low melting it ( 420°C) Substrate Diffusion zone varying coating thicknesses; the cross sections on theright side show exemplarily the resulting coatings: Severe Cl‐attack arises with the eutectic concept – especially (Fe,Ni) 2 Al 5 is leached out – whereas hardly any attack occurs with the barrier concept, where nearly all of the coating transformed into the more corrosion resistant (Fe,Ni)Al‐phase Results – coating behavior in a cement plant Test conditions: - Temperature at the anchor tip ≈ 800°C, 10 month Anchors coated with the eutectic concept and the barrier concept Testing parameters in the laboratory point (≈420°C) A dense liquid phase forms on top and the Al in the eutectic composition can form Al 2 O 3 ‐ Barrier concept: Forming a glas barrier on top of the aluminum particles With a dense glass/ceramic layer only a small amount of oxygen can reach the aluminum or the base material, so the oxygen diffusion is restrained Material: 1.4876 / alloy 800H / X10NiCrAlTi32‐20 - Anchors coated with the eutectic concept and the barrier concept - Prediffusion in air or coated directly in the plant - Measurement of diameter-loss at the anchor tip and 15 mm below Uncoated anchor before exposure Uncoated anchor after exposure 15mm T 150°C 3h 350°C 3h 500°C 3h 800°C, 300h Atmosphere: N 2 / 200ppm HCl/ 20ppm SO 2 / 8Vol%O 2 /15Vol%H 2 O Diffusion time: 300h solid state diffusion to form stable phases Heating process: similar to the heating up in waste‐to‐energy plants Fig. 6: Uncoated anchor before (a) and after (b) exposure as well as anchors after slurry coating directly in the plant before exposure (c) Fig.7: Mean diameter loss of anchors after exposure in the plant Acknowledgement This work was funded by the German Ministry of Economics and Technology through the German Federation for Industrial Research (“Arbeitskreis industrieller Forschungs‐ vereinigungen”, IGF‐Nr. 17471 N), which is gratefully acknowledged. Fig.4: Schematic heating process for diffusion; the parameters were chosen similar to the heating up in waste‐ to‐energy plants; the long diffusion time is due to solid state diffusion in order to form stable phases t Both concepts show a significant reduction in comparison to un‐ coated samples
Transcript of Corrosion resistant coatings for refractory lining …...Corrosion‐resistant coatings for...
Corrosion‐resistant coatings for refractory lining anchors in aggressive high temperature environmentstemperature environments
J.T. Bauer, M.C. Galetz, M. Schützee‐mail: [email protected] by: BMWI via AiF
Period: 01.04.2012 – 31.07.2015
MotivationMotivation
In a large number of technical incineration processes metallic components are in contact with aggressive gases anddeposits. Especially critical are atmospheres containing halogens such as chlorine, alkalis, and heavy metalcompounds, all of which cause severe corrosion damage.
Aluminizing of the metallic components is a promising way to protect them. Slurry aluminizing was chosen as coatingtechnique because it is a well established, low‐cost process even for large components.
The challenge in the present project is to develop corrosion‐resistant slurry diffusion coatings in situ, directly inplants, using the process‐inherent energy for the diffusion process.
The protection of refractory lining anchors is of special interest (Figs. 1 and 2), but the coating solutions for thisapplication can also be transferred to other metallic components such as sheets or tubes. Osthövener, Kollenberg, 2007pp p
Coating concepts for Al diffusion in aggressive environment
Fig.1: Anchors forrefractory linings
Based on a two‐layer system of layer 1, diffusing metal (AlSi slurry) andlayer2, protection of the base material and the diffusing metal fromoxidation/corrosion, three coating concepts are evaluated (Fig. 3):
Fig.2: Bursting of the refractory liningand corroded anchors
Results – laboratory
50µmSubstrate
Diffusion zone
Al
AlAl
Ge Al
Glass
50µm
Substrate
Diffusion zone
50µm
„Eutectic concept“„Barrier concept“„Oxygen getter concept“
Fig.5: Relationship of the cumulative probability of thesurface coverage and the coating thickness; only the barrierconcept leads to a homogenous diffusion coating, whereasthe other coating concepts lead to a broader distribution of
i ti thi k th ti th i ht
Fig.3: Three coating concepts based on a two‐layer system
‐ Oxygen getter concept: Large AlSi powder particles are used for the diffusion layer,smaller Al powder particles (3‐5µm) with larger surface are used as oxygen getter Formation of Al2O3 on top
‐ Eutectic concept: AlSi powder particles are used for the diffusion layer, Ge powderparticles as second layer are used to form a eutectic composition with a low melting
i t ( 420°C)
Substrate
Diffusion zone
varying coating thicknesses; the cross sections on the rightside show exemplarily the resulting coatings: Severe Cl‐attackarises with the eutectic concept – especially (Fe,Ni)2Al5 isleached out – whereas hardly any attack occurs with thebarrier concept, where nearly all of the coating transformedinto the more corrosion resistant (Fe,Ni)Al‐phase
Results – coating behavior in a cement plantTest conditions:
- Temperature at the anchor tip ≈ 800°C, 10 monthAnchors coated with the eutectic concept and the barrier concept
Testing parameters in the laboratory
point (≈420°C) A dense liquid phase forms on top and the Al in the eutectic composition canform Al2O3
‐ Barrier concept: Forming a glas barrier on top of the aluminum particlesWith a dense glass/ceramic layer only a small amount of oxygen can reach thealuminum or the base material, so the oxygen diffusion is restrained
Material: 1.4876 / alloy 800H / X10NiCrAlTi32‐20
- Anchors coated with the eutectic concept and the barrier concept- Prediffusion in air or coated directly in the plant
- Measurement of diameter-loss at the anchor tip and 15 mm below
Uncoated anchor before exposure
Uncoated anchor after exposure 15mm
T
150°C3h
350°C3h
500°C3h
800°C, 300h
Atmosphere: N2/ 200ppm HCl/ 20ppm SO2/ 8Vol%O2/15Vol%H2O Diffusion time: 300h solid state diffusion to form stable phasesHeating process: similar to the heating up in waste‐to‐energy plants
Fig. 6: Uncoated anchor before (a) and after (b) exposure as well as anchors after slurry coating directly in the plant before exposure (c)
Fig.7: Mean diameterloss of anchors afterexposure in the plant
AcknowledgementThis work was funded by the German Ministry of Economics and Technology through the German Federation for Industrial Research (“Arbeitskreis industrieller Forschungs‐vereinigungen”, IGF‐Nr. 17471 N), which is gratefully acknowledged.
Fig.4: Schematic heating process for diffusion; the parameters were chosen similar to the heating up in waste‐to‐energy plants; the long diffusion time is due to solid state diffusion in order to form stable phases
tBoth concepts show asignificant reductionin comparison to un‐coated samples
