The plant exposures have shown that weld overlays of alloy 625 exhibit promising behaviour in a number of plants, i.e. under strong sufidising and chloridising conditions, and in the temperature ranges chosen. It is also immediately clear that all cast austenitic stainless steel grades exhibit intergranular attack by sulphur and/or chlorine. The behaviour of the thermal spray coating implies that the Ni-FeCrSiCe is the most promising solution. Preoxidation has some effect, as shown in the exposures of preoxidised tubes and rings in the Schweinfurt plant. It was shown by in-plant exposure that preoxidising of AC 66 reduces corrosion by a factor of about 20 %.
Biowas — Materials for increased performance in sustainable fuel combustion
HCl-induced high temperature corrosion under thermal cycling conditions has been studied for iron/carbon steel, nickel and chromium together with two austenitic steels (304 and 310). Experiments were conducted with 14 cycles at 700 °C and with 49 cycles at 400 °C. The hot dwell time was 20 hours and cold dwell time approximately 4 hours. Both as-ground and materials preoxidised at either 400 °C or 700 °C were exposed. A large difference in growth rate kinetics was seen when experiments at 400 °C and 700 °C were compared. At 700 ºC, iron and carbon steel had a gross mass change up to around 400 times higher than the austenitic 310 steel. However, at 400 ºC the difference was only 5 to 10 times higher. With almost no exceptions, materials preoxidised at 400 °C exhibited the lowest corrosion rate and a better oxide adhesion. Preoxidation at 700 °C had a similar beneficial effect in testing at 400 °C, but no obvious positive impact at 700 °C.
EC
The fundamental investigations have shown that preoxidation of pure metals (Fe, Ni, Cr) and alloys is beneficial if the metal forms an oxide different from iron oxide. Iron oxide, formed on iron, is easily penetrated by chlorine, thereby initiating the mechanism of ‘active oxidation’. Nickel, which is preoxidised in SO2-containing gases, is also not protective, because NiSO4 is formed, which is converted to NiCl2 upon exposure to HCl-containing gas.
KI-NA-23868-EN-S
The aim of the project was to identify suitable material as well as weld overlays and thermal spray coatings for service in high temperature combustion plants, i.e. waste and biomass incineration and a cement kiln plant. The project combines investigation in the laboratory on fundamentals of oxide scale breakdown and the effect of preoxidation as well as laboratory exposures in simulated combustion environments and in-plant exposures in combustion plants.
Price (excluding VAT) in Luxembourg: EUR 20
Biowas — Materials for increased performance in sustainable fuel combustion
EUR 23868
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EUROPEAN COMMISSION Directorate-General for Research Research Fund for Coal and Steel Unit Contact: RFCS publications Address: European Commission, CDMA 0/124, B-1049 Brussels Fax (32-2) 29-65987; e-mail:
[email protected]
European Commission
Research Fund for Coal and Steel Biowas Materials for increased performance in sustainable fuel combustion H. Asteman, M. Spiegel (1), S. Vodegel (2), R. Kull (3), R. Pettersson (4), G. Pimenta (5), I. Azkarate (6), G. Paradisi (7), F. Mancia (8) (1) Max-Planck-Institut für Eisenforschung GmbH (MPIE) — Max-Planck-Straße 1, 40237 Düsseldorf, Germany (2) Clausthaler Umwelttechnik Institut GmbH (CUTEC) — Leibnizstraße 23, 38678 Clausthal-Zellerfeld, Germany (3) Universität Stuttgart (USTUTT) — Keplerstraße 7, 70174 Stuttgart, Germany 4 ( ) Korrosions- och Metallforskningsinstitutet AB (KIMAB) — Drottning Kristinas väg 48, 11428 Stockholm, Sweden (5) Instituto de Soldadura e Qualidade (ISQ) — Av. Prof. Cavaco Silva N.° 33, 2780-920 Porto Salvo-Oeiras, Portugal (6) Fundación INASMET (INASMET) — Paseo Mikeletegui 2, Barrio Igara, 20009 San Sebastian-Guipuzcoa, Spain (7) Actelios SpA, Gruppo Falck (TTR) — Via Alberto Falck 4–16, 20099 Sesto San Giovanni, Italy (8) Centro Sviluppo Materiali SpA (CSM) — Via di Castel Romano 100/102, 00128 Rome, Italy
Contract No RFSR-CT-2003-00020 1 September 2003 to 28 February 2007
Final report
Directorate-General for Research
2009
EUR 23868 EN
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A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server (http://europa.eu). Cataloguing data can be found at the end of this publication. Luxembourg: Office for Official Publications of the European Communities, 2009 ISBN 978-92-79-11555-4 ISSN 1018-5593 doi 10.2777/47060 © European Communities, 2009 Reproduction is authorised provided the source is acknowledged. Printed in Luxembourg Printed on white chlorine-free paper
Table of contents Table of contents
3
Final summary
5
1. Preparation of samples
5
2. Conclusions from the laboratory testing and mechanistic studies
7
3. Conclusions from plant studies and exposures
9
4. General conclusions
13
Scientific and technical description of the project
14
1. Objectives of the project
14
2. Comparison of initially planned activities and work accomplished
14
3. Description of activities and discussion
15
WP1a: Supply of commercial alloys
15
WP1b: Preparation of coatings 1), laboratory heats 2)
15
1. Production of coatings by welding
15
2. Production of coatings by HVOF
18
3. Production of laboratory heats
20
WP2: Mechanistic studies of oxide scale breakdown
21
1. Isothermal tests
21
2. Cyclic oxidation tests
28
WP3: Laboratory exposures
40
WP4: Exposures in test-plants
52
1. Exposures and analysis of samples exposed in the CUTEC pilot plant
52
2. Investigations of operating parameters on deposit formation
56
WP5: Field exposures
66
1. Exposures in the cement kiln plant
66
2. Exposures in the Portucel Biomass Boiler
82
3. Exposures in the GKS Schweinfurt plant
92
3
4. Measurements with a corrosion probe in the GKS Schweinfurt plant
94
5. Exposures of pre-oxidised and not pre-oxidised AC66-tubes
107
6. Conclusions
109
7. Exploitation and impact of the research results
109
List of figures and tables
110
List of references
115
4
Final summary The final summary gives an overview of the major outcome of the project. It has to be noted that the summary does not completely follow the workpackages, as described in the technical annex, but comprises the workpackages as follows:
1. Preparation of samples The six materials listed in table 1 were obtained from Sandvik Materials Technology (SMT) and Outokumpu Stainless AB (OS). Table 1: Designation, product form and compositions of the chromia forming alloys [wt.-%]
EN B1 B2 B3 B4 B5 B6
1.4982 1.4845 1.4845 1.4835 1.4835 1.4563 1.4982 1.4845 1.4835 1.4863
Comm. name
Produ cer
Dimension.
Esshete 1250 310 (25-20) 310S 253MA 253MA Sanicro28/ C-steel
SMT OS SMT OS SMT SMT
63 x 5 mm tube 3 mm sheet 73x9 mm tube 3 mm sheet 88x6mm tube 50x(3+3) mm Compound tube
Si % 0.5 0.5 0.5 1.6 1.6 -
Mn % 6 1 1 0.6 0.6 -
Cr % 15 25 25 21 21 27
Ni %
Mo %
Other
10 19 19 11 11 31
3.5
V N,Ce N,Ce Cu
X10CrNiMoMnNbVB15-10-1 X 12 CrNi 25-21 X9CrNiSiNCe21-11-2 X1NiCrMoCu31-27-4
INASMET has produced by welding two nickel base alloys coatings on carbon steel C ≤ 0.20, Si ≤ 0.55, Mn ≤ 1.60 in order to provide a more corrosion resistant surface. The two nickel base alloys have been deposited by 2 different welding methods: SMAW (Shielded Metal Arc Welding, manual) and GMAW-MIG (Gas Metal Arc Welding-Metal Inert Gas, automatic). Table 1 summarizes the overlay type and welding specifications. Table 2: Welding procedures and specifications
Weld overlay type Inconel 625
Hastelloy C276
Welding process SMAW (manual) GMAW-MIG (Automatic)
SMAW (manual) GMAW-MIG (Automatic)
Inconel 625 Hastelloy C276
2.4856 2.4819
Electrode (classification) Electrode ENiCrMo-3 Wire Electrode ENiCrMo-3 Electrode ENiCrMo-4 Wire Electrode ENiCrMo-4
NiCr 22 Mo 9 Nb NiMo 16 Cr 15 W
5
Procedure specific. (ASME IX) W-In 625/111 W-In 625/131 W-C276/111 W-C276/131
Weld layers 2 weld layers. Total thickness overlay 6-7mm
Powders and thermal spray coatings were produced in CSM facilities by Vacuum Induction Inert Gas Atomisation with chemical composition shown in table 3. For the present project, a powder 40-75 micron is produced, suitable to HVOF spraying technology.
Table 3: Chemical compositions of powder and coatings produced
Powder
Alloy
Fe %
Ni %
C %
Cr %
Al %
Si %
Ce ppm
CSM - A
FeCrAl
base
-
0.0080.01
20-22
5.56.5
-
-
CSM - B
FeCrSi
base
-
0.0080.01
24-26
-
4.55.5
-
CSM - C CSM - D
NiFeCrAlCe NiFeCrSiCe
9.78 23.8
base base
0.01 0.01
25.3 28.8
2.07 -
3.0
100 124
Production of laboratory heats were prepared by MPIE. For the chemical content in weight %, see table 4 (Please note that Fe is in balance).
Table 4: Chemical composition of the laboratory melts [wt.-%]
Name: MPIE890 MPIE891 MPIE V60/12 MPIE V60/13
Cr (%) 9.5 9.5 9
Al (%) 2.56 2.58 2.5
Mo (%) Ni-FeCrAlCe> FeCrSi >FeCrAl
•
Stainless steel 12RM80 shows the highest general corrosion rate in the cement kiln plant at the two established temperatures. The following ranking could be established, starting with the most corrosion resistant stainless steels: 253 MA sheet 10R19 (253MA) Tube ≈ AISI 310 Sheet 7RE10 (310S) Tube ≈ Sanicro 28/4L7 Tube 12RM80 Tube
•
SANICRO 28/4L7 stainless steel shows the highest depth of intergranular attack (internal penetration).
•
For the six stainless steels studied, intergranular penetration is mainly due to the formation of chromium rich sulphides, except for the 12RM80 and SANICRO 28/4L7 stainless steels for which internal penetration is mainly due to the precipitation of chromium oxides.
The major corrosion mechanism was attributed to high temperature sulfidation.
9
Conclusions from exposures in the Portucel biomass plant: The results from the this plant were only evaluated for the cast materials as shown in table 1 as well as for the IN-625 weld overlay. The samples of Hastalloy C-276 could not be found after exposures and the thermal spray coatings as supplied by CSM are still in plant due to late delivery. The samples exposed can be divided in three categories: Weld overlays of Alloy 625 and Hastalloy C-276 exhibit severe corrosion. Especially C-276 could not be found any more after the exposure due to complete corrosion of the sample after the trial. Alloy 625 show severe chlorine induced corrosion along the dendritic microstructure. The difference between this two alloys is the higher iron content of C-276, leading to more corrosion, as already reported after exposure in the cement kiln plant. 253MA (sheet) and 310 sheet materials: the big majority of these samples did not withstand medium or long term exposures. Already after approximately 4300h the coupons were strongly oxidised. After about 11200h only to samples of 310 material and one of 253MA were recovered. All the remaining samples of these materials were completely converted to oxides or only a residual amount of metal was present. 10R19, 12RM80, 7RE10 and Sanicro 28 materials resisted quite well to the long term exposure in terms of resistance to this corrosive environment. Sanicro 28 and 12RM80 developed a compact and quite uniform oxide layer that act as a diffusion barrier for chlorine and, therefore, slowed down the corrosion processes. All the cast materials tested show the same type of degradation mechanism, i.e. intergranular corrosion. A differentiating factor among the different materials is the depth of the intergranular penetrations. While Sanicro 28 and 12RM80 do not show significant penetrations, the 310 material shows extended penetration over many grains in depth. The major attack of all cast alloys is grain boundary oxidation, as already observed in the cement kiln plant. The significant difference is between the cement kiln plant and the Portucel plant is the corrosion mechanisms. As chlorine and potassium were found in the deposits on all samples, and at the grain boundaries, the major corrosion mechanism is chlorine induced ‘active oxidation’
10
Conclusions from exposures in the Cutec pilot plant •
Inconel 625 overlays show a better corrosion resistance in the CUTEC pilot plant with respect to the HC-276 overlays. This is attributed to the higher iron content of the HC-276 coating with respect to the iron content of the Inconel overlay. SEM/EDS examinations of Inconel 625 overlays indicate that the external scale layer is mainly constituted of chromium oxide. Intergranular penetration is due to the formation of chromium and nickel oxides.
•
EDX analysis of HC-276 overlays show that the surface oxides and the internal corrosion products mainly consists out of Cr-Ni-Mo oxides.
Conclusion from exposures GKS SCHWEINFURT PLANT A very slight corrosion is observed for HC-276 and Inconel 625 overlays when exposed to the environmental conditions of the SCHWEINFURT plant, thus indicating a good corrosion resistant in this specific environment. •
Thermal spray coatings: •
After exposure (450 °C: 165 h, 280 h) Coating A (21Cr 6Al) shows already a deep corrosive attack by chlorine-induced corrosion. After 280 h of exposure half of the coating is damaged and the structure of the attacked outer layer is very porous. Furthermore regarding corrosion resistance Coating A shows at a decreased material temperature of 400 °C (165 h) no substantial improvement.
•
After exposure (450 °C: 165 h, 280 h) Coating B (25Cr 5Si) is also attacked by chlorine-induced corrosion. After 280 h of exposure approx. 1/3 of the coating is damaged and in comparison to Coating A the oxidized outer layer is less porous. Furthermore regarding corrosion resistance Coating B shows at a decreased material temperature of 400 °C (165 h) no substantial improvement.
•
After exposure (450 °C: 165 h, 280 h) Coating C (Ni-9.5Fe 25Cr 2Al Ce) already shows a very deep corrosive attack by Chlorine-Induced Corrosion. After 165 h of exposure more than half of Coating C is damaged and the structure of the attacked outer layer is very porous. After 280 h of exposure Coating C is totally destroyed and the tube material (P5) is also attacked by Chlorine Induced Corrosion. Cracks in the Coating C were also detected at several positions.
•
After exposure (450 °C: 280 h) Coating D (Ni-23Fe 28Cr 3Si Ce) is not damaged by corrosion. The coating is mainly unattached and the chemical composition is not changed. Cracks and pores in Coating D are also not detected.
The results from exposures of the thermal spray coating in Schweinfurt and in the cement kiln plant correlate quite well i.e. Ni-23Fe28Cr3SiCe behaves best.
11
Effect of preoxidation In the case of rings of 13CrMo4-5 that were preoxidized in the Chlorine-enrichments were found, but were separated by an oxide scale from the steel itself. This indicates that preoxidation of the material might be beneficial. On the basis of that finding, a comparison of pre-oxidised and not pre-oxidised tubes of AC 66 has been done in the waste incineration plant in Schweinfurt for about 11 month. The wall thickness of the tubes was measured around the tube at four places spread over the length of the tube. The material losses are shown in figures 2 and 3.
Figure 2: Material loss from an AC 66 tube without pre-oxidation
In this application and operation period the material loss from the pre-oxidised AC 66 tube was nearly 20 % lower (0.32 mm / 1,000 oh) than from the tube without pre-oxidation (0.41 mm / 1,000 oh).
12
Figure 3: Material loss from an AC 66 tube with pre-oxidation
4. General conclusions The plant exposures have shown that weld overlays of Alloy 625 exhibit promising behaviour in a number of plant i.e. under strong sufidising and chloridising condition and in the temperature ranges chosen. It is also immediately clear that all cast stainless steel grades exhibit intergranular attack by sulphur and/or chlorine. The situation of the thermal spray coating imply the Ni-FeCrSiCe is the most promising solution. Preoxidation, especially at lower temperatures has some effect, as shown in the laboratory experiments and in the exposures of preoxidised tubes and rings in the Schweinfurt plant, which corroded 20% less than non-preoxidised materials.
13
Scientific and technical description of the project 1. Objectives of the project Environmental considerations means that an increasing number of plants are being built for the combustion of renewable energy resources such as waste and biomass. This trend has accelerated due to recent legislative restrictions on dumping of waste, also to the introduction of lower taxes on electricity produced from sustainable fuels. One factor that all these combustion processes have in common is that they result in very corrosive high temperature environments. Chlorides are usually the dominant aggressive species, and the situation is also exacerbated by the presence of solid or molten ash deposits. Corrosion in such plants has led to many failures and unscheduled shut-downs for replacements, so appropriate materials selection and development of improved new alloys is a vitally important part of future development. The project aims to an understanding of mechanisms of oxide scale breakdown with respect to the use of preoxidation as a method of alloy protection. It provides data from laboratory and field runs to facilitate the selection and use of existing stainless steels and coatings for demanding service conditions in waste and biofuel combustion plants. The development and selection of suitable materials for the described severe service conditions will improve also the reliability of thermal plant, so allowing a better and constant control of running conditions (physic and chemical process parameters). The use of more resistant materials facilitates the attainment of this peculiar target, as the flexibility of plant is improved.
2. Comparison of initially planned activities and work accomplished Deviations from the initial plan concern: •
preoxidation treatments were not carried out in CO2 containing gases for laboratory reasons (no supply of CO2). It was expected, that preoxidation in CO2-containing gas leads to the formation of carbonates within the oxid scale. The carbonate will be converted to chlorides upon subsequent chloridation.
•
plant exposures could not be fully evaluated because samples can only be placed/removed during shut-down. In some cases (exposure of coatings) this shut-down periods are not scheduled as foreseen
14
3. Description of activities and discussion WP1a: Supply of commercial alloys The six materials listed in Tab. 1 were obtained from Sandvik Materials Technology (SMT) and Outokumpu Stainless AB (OS).
Table 1: Designation, product form and compositions of the chromia forming alloys
EN
Comm. name Producer
Dim.
Si %
Mn %
Cr %
Ni %
Mo %
Other
B1
1.4982
Esshete 1250
SMT
63 x 5 mm tube
0.5
6
15
10
-
V
B2
1.4845
310 (25-20)
OS
3 mm sheet
0.5
1
25
19
-
-
B3
1.4845
310S
SMT
73x9 mm tube
0.5
1
25
19
-
-
B4
1.4835
253MA
OS
3 mm sheet
1.6
0.6
21
11
-
N,Ce
B5
1.4835
253MA
SMT
88x6mm tube
1.6
0.6
21
11
-
N,Ce
B6
1.4563
Sanicro28/ C-steel
SMT
50x(3+3) mm Compound tube
-
-
27
31
3.5
Cu
WP1b: Preparation of coatings 1), laboratory heats 2) 1. Production of coatings by welding Weld metal overlay is the application of weld passes on the surface of a metal component which allows the weld material to fuse with the base material forming a metallurgical bond. Generally the overlay is applied with one to three weld beads. INASMET has produced by welding two nickel base alloys coatings on S355J2G3 carbon steel (St52-3/ 1.0570) C ≤ 0.20, Si ≤ 0.55, Mn ≤ 1.60 in order to provide a more corrosion resistant surface. The two nickel base alloys have been deposited by 2 different welding methods: SMAW (Shielded Metal Arc Welding, manual) and GMAW-MIG (Gas Metal Arc Welding-Metal Inert Gas, automatic). Table 2 summarizes the overlay type and welding specifications. The chemical composition of the used filler metals is shown in table 3.
15
Table 2: Welding procedures and specifications.
Weld overlay type
Welding process
Electrode (classification)
Inconel 625
SMAW (manual) GMAW-MIG (Automatic)
Electrode ENiCrMo-3 Wire Electrode ENiCrMo-3 Electrode ENiCrMo-4 Wire Electrode ENiCrMo-4
Hastelloy C276
SMAW (manual) GMAW-MIG (Automatic)
Procedure specific. (ASME IX) W-In 625/111 W-In 625/131
Weld layers 2 weld layers. Total thickness overlay 6-7mm
W-C276/111 W-C276/131
Table 3: Chemical composition of filler metals (wt. %)
Filler metals (%Wt) Inconel 625 covered electrode (ENiCrMo-3) Inconel 625 wire electrode (EniCrMo-3) C-276 covered electrode (EniCrMo-4) C-276 wire electrode (EniCrMo-4)
C %
Fe %
Mo %
0.022
2.50
8.98
0.012
0.05
9.10
W %
Mn %
NbTa %
Si %
20.94 63.80
-
-
3.30
0.31
22.29
-
-
3.49
0.26
Cr %
Ni %
Bal
