A REVIEW OF EXPERIENCES WITH AL-6XN AND ZERON 100 ALLOYS IN AIR POLLUTION CONTROL SYSTEMS

Transcription

1 A REVIEW OF EXPERIENCES WITH AL-6XN AND ZERON 100 ALLOYS IN AIR POLLUTION CONTROL SYSTEMS D. Wachow iak J. Wilson Rolled Alloys 125 West Sterns Road Temperance, M I 48182

2 A REVIEW OF EXPERIENCES WITH AL-6XN AND ZERON 100 ALLOYS IN AIR POLLUTION CONTROL SYSTEMS D. Wachow iak J. Wilson Rolled Alloys 125 West Sterns Road Temperance, M I Abstract Coal fired power plants are faced with increasingly strict air quality control laws and EPA rules. New multi-pollutant legislation is controlling a wider range of emissions, especially sulfur compounds. A significant number of flue gas desulfurization (FGD) units worldwide employ wet scrubbing to reduce sulfur dioxide emissions by more than 90 percent. Wet scrubbing has also been found to be effective at removing mercury in many cases. Due to the inherent contaminants generated by the combustion of coal, wet FGD s require the use of corrosion resistant materials in their construction. A variety of metallic corrosion resistant alloys are currently used in these pollution control systems. This paper will review the use of AL-6XN and ZERON 100 alloys in various FGD applications around the world. Examples of AL-6XN and ZERON 100 in actual service in FGD units will be presented. AL-6XN and ZERON 100 are alloys that have been chosen for these systems when conditions are too severe for either 317L stainless steel or 2205 duplex stainless steel. Experimental data will be reviewed that supports the use of these alloys in the high chloride containing environments encountered by the many components of the pollution control systems. AL-6XN and ZERON 100 alloys have proven to be cost effective materials of construction that fill the gap between the lower alloyed stainless steels such as 317L, and 2205, and the high molybdenum and nickel based alloys such as C-276. As AL-6XN and ZERON 100 alloys are established materials of construction that are readily available in product forms necessary to complete an FGD system. Introduction Coal fired power plants currently generate nearly half of the electric power in the United States. Combustion of coal generates NOx, SO2, particulates, and other pollutants that contaminate the environment. These coal fired power plants are being faced with increasingly stricter air quality control laws and EPA rules mandating the reduction of a wide range of pollutants especially

3 sulfur compounds. Thus, it is clear that pollution control will remain a major concern for the power generation industry for many years. The most effective way to significantly reduce emissions of SO2, and in some cases mercury, is through the use of flue gas desulfurization (FGD). There are several FGD methods available, examples include various dry scrubbing methods, sea water scrubbing, and wet scrubbing with lime or limestone. The majority of the scrubbers currently being installed use the wet limestone technology. This method is the best suited to scrubbing the high volume of flue gas emitted by large power plants. In addition, this method has the added advantage of allowing for the production of wallboard quality gypsum, which can be sold to partially offset the cost of scrubbing. The corrosive conditions within an FGD are complex, with many factors contributing to the severity of the environment. The selection of an appropriate material will depend on the operating parameters of the system as well as the environment surrounding the specific components. The most important corrosive species generated during the combustion of coal are chlorides and fluorides along with sulfur bearing species. Contributing to the corrosive environment is the temperature, acid dew point, ph, crevice forming deposits, slurry additives, etc. Typically, several alloys are used in a system, which will be matched to the conditions under which a component is operating. Fortunately, extensive operating experience has been generated which can be used as guide to selecting appropriate materials of construction. The purpose of this paper is to review the properties and corrosion resistance of the 6% Mo alloy, AL-6XN alloy (UNS N08367) and the super duplex ZERON 100 (S32760), in relation to pollution control systems. In addition, typical current applications of the N08367 and S32760 alloys in the FGD systems are described. Backgr ound Several alloys have been used in FGD systems ranging from the 300 series stainless steels to the high nickel based alloys. Some of these alloys are listed below in Table 1. The appropriate alloy of construction will depend on the operating conditions and location within the equipment. In the case of the absorber inlet, shown in Figure 1, the hot flue gas passes through the sulfuric acid dew point, leading to the condensation of hot, concentrated sulfuric acid. In this aggressive environment, a nickel alloy with a high content of molybdenum is necessary. The vast majority of absorber inlets in the world are made of N10276 alloy. The material of construction for the absorber tower is largely dependent on the chloride content of the slurry. Fluorides may also be present, which can be considered to be approximately the same as chlorides with regard to their effect on pitting of stainless steels. Since the fluoride content is usually very low, discussion of the effect of halides will be limited to chloride content. The chloride content of the slurry is largely determined by the chloride concentration of the coal being burned, and the rate at which fresh water is added to the slurry (blow down). In cases where a high blow down rate is not possible, e.g. where water treatment is inadequate, the slurry chloride content may become very concentrated.

4 Table 1: Nominal Composition (wt. %) of Stainless Steels and Nickel Based Alloys used in FGD Systems UNS Number Alloy Cr Mo Ni Fe Other Duplex S Bal 0.16N S32760 ZERON Bal 0.22N Austenitic S L Bal S LMN Bal 0.15N Superaustenitic N08367 AL-6XN Bal 0.22N Ni Based N Bal 4 4(Cb+Ta) N Bal 5.5 4W N Bal 4 3W, 1.7Co Table 2: Temperature for Initiation of Crevice Corrosion in 10% Ferric Chloride (FeCl 3 6H 2 O) Solution per ASTM G 48 Practice B; PRE N = Cr + 3.3Mo + 16N UNS Number F ( C) PRE N S (2) 28 S (20) 35 S (20) 35 S (40) 41 N (43) 45 N (45) 51 N (55) 69 N (55) 65

5 A useful way of ranking the resistance of a material to chlorides is through the Pitting Resistance Equivalent, PREN. Equation 1 gives a common formula for calculating the PREN for austenitic and duplex stainless steels. The elements Cr, Mo, and N provide resistance, especially when present together (1-3). Nitrogen is particularly effective in the superaustenitic alloys with high Mo content (4-6). PREN = Cr + 3.3Mo + 16N (1) The higher the PREN, the more resistant the alloy is to pitting and crevice corrosion in the presence of chlorides. Typical PREN values for various alloys are shown in Table 2 on the previous page. By listing the alloys by decreasing PREN, the 6% Mo alloys and super duplex stainlesses are positioned above (more resistant than) the conventional stainless steels and approaching the nickel alloys. Figure 1. Schematic of an FGD system The absorber outlet ducting will be exposed to some slurry carry over from the absorber as well as residual SO3 from the flue gas. Since the temperature in the absorber outlet is typically well

6 below the sulfuric acid dew point, low ph condensates containing chlorides are often present. Thus, a Ni-Cr-Mo alloy, such as N10276 or N06022, is often employed. However, the increased efficiency and improved design of modern scrubbers somewhat alleviates this issue, allowing for the application of stainless steels in some cases. A plot demonstrating the corrosion resistance of various alloys in sulfuric acid is given in Figure 2. The presence of chlorides in conjunction with sulfuric acid will generally increase the corrosion rate. Figure 2. Corrosion resistance of alloys in sulfuric acid. Lines indicate a corrosion rate of 0.1mm/yr (4mpy) A general guide for alloy selection for FGD absorber towers is presented in Figure 3. This table applies to a temperature range of 50 C 60 C (120 F 150 F) and a fluoride content of less than 50 ppm. This table is based on the open literature on the subject and is intended to be used as a guide only. Factors such as deposit formation, fabrication procedures, contaminants, additives, etc., must also be taken into consideration when selecting the appropriate material.

7 N08637 Superaustenitic Figure 3. Alloy selection chart for FGD absorber towers In the early 1970s UNS N08366 alloy, containing 6.3Mo, along with 20Cr and 24Ni, was introduced (7). Used primarily as welded power plant condenser tube in seawater, this material performed well in the high chloride environment (8-9). High Cr and Mo provided excellent resistance to pitting and crevice corrosion but also promoted intermetallic phases. This limited the thickness at which the material could be produced to thin gauges, such as that used for condenser tubing. Nitrogen suppresses intermetallic phases (10-11) and 0.2 percent was shown to be beneficial to the 20Cr 24Ni 6.3Mo alloy. Nitrogen also improves pitting resistance and increases strength. These benefits, incorporated into the N08367 alloy in the early 1980s, permitted a full range of product forms and much broader applicability. The N08367 alloy has found may uses in power plants (12-13), oil refineries, chemical and petrochemical plants, and pulp mills, as well as in a variety of seawater applications. Not all alloys in the 6Mo family contain N, and some have a higher or lower nickel content than N08367 alloy. Some other 6Mo alloys also contain Cu which may cause intergranular attack in high chloride environments. All of these alloys have a low carbon content ( L grades), and thus, are highly resistant to sensitization and intergranular corrosion. S32760 Super Duplex The first duplex stainless steels, developed in the 1920 s, lacked toughness and ductility, and thus, were of little utility. Development of modern duplex stainless steels began in the late 1970 s with the expanded commercial use of the AOD (Argon Oxygen Decarburization) process, which among other things permitted the controlled addition of nitrogen. The wide spread usage of duplex alloys was further driven by the sharp escalation in raw material prices during the mid 2000 s, resulting in their wide spread use as a cost effective upgrade over traditional austenitic alloys. The standard duplex alloy, namely UNS S32205, has been the chosen alloy for many FGD systems in the past decade. The 25Cr alloy, known commercially as 255, saw its first extensive FGD application in the United States at Gibson Station in the mid 1980 s. The good performance of this alloy in this application has lead to more widespread use elsewhere. The Super Duplex alloys S32750 and S32760, commercially know as 2507 and ZERON 100, respectively, have been widely and successfully applied in Oil and Gas and Desalination applications for many years. More recently, these alloys have gained acceptance in the FGD community and are being applied in environments where excellent corrosion resistance is needed.

8 The duplex name comes from the fact that the alloys develop a microstructure containing approximately equal amounts of austenite and ferrite phases. The duplex microstructure results in properties that are a combination of those of ferritic and austenitic alloys. The first widely available super duplex stainless steel was developed by Gradwell and coworkers in the mid 1980 s. This alloy was called ZERON 100 and was developed as a casting alloy (J93380) for pump applications in the oil and gas industry. The performance of the steel in this application generated a demand for the alloy in wrought product forms also. As demand for the steel grew, clients called for ASTM, NACE, British Standards and other codes to include and cover the ZERON 100 range of products. Moreover, with the introduction of the EC Procurement Directive in 1993, it became an exception for clients to specify any trade name in requests for quotation and a generic description for the alloy was required for the business to continue. In , ASTM considered the properties of several heats of ZERON 100 in a range of product forms and on the basis of this designated the code UNS S32760 to the alloy and introduced this number into several standards. Finally, in 1997, UNS S32760 was listed in ASME complete with applicable design stresses. These listings were again based upon the properties of the proprietary alloy. Fabr ication Char acter istics Both the N08367 and S32760 alloys are readily welded to itself, other stainless steels, nickel based alloys, and carbon steel. Segregation occurs in as-cast matching-composition weld metal, leaving areas which are low in Cr and Mo, making them susceptible to pitting. For this reason a weld filler metal with -higher Mo content is needed for proper as welded corrosion resistance. Nickel alloy 625 (AWS ERNiCrMo-3) filler metal and 112 (AWS ENiCrMo-3) electrodes provide welds with corrosion resistance and mechanical properties generally comparable to the N08367 alloy base metal. Other high-mo, nickel-base filler metals, such as N01276 alloy are also suitable. S32760 can also be readily welded using a matching composition ZERON 100X filler metal, which overmatches the base metal with more nickel to ensure proper phase balance after welding in complete without the need to anneal afterwards. Both the N08367 and S32760 also have good ductility to be formed into various shapes and sizes needed to fabricate equipment necessary within the FGD absorber. L abor ator y Testing Both the N08367 and S32760 alloys have been tested in various conditions that represent conditions that can be seen in FGD environments, including high chloride and fluoride environments, sulfuric acid mixed with chloride environments and other severe environments that take into effect the elevated temperatures, lower ph and various amounts of chloride and acid levels within the FGD system.

9 N08367 Laboratory Testing Extensive testing has been performed comparing N08367 alloys to stainless steels and higher Ni- Mo alloys. The testing includes standard ASTM corrosion testing as well as specialized testing intended to simulate FGD environments. Data from some of these tests are shown in the following tables. An indication of the pitting resistance is given by the ferric chloride crevice corrosion data shown in Table 2, which is generated using test method ASTM G48-B. The capability of the N08367 alloy with 6.2Mo is seen to be close to that of nickel-base N06625 alloy (9Mo) and significantly better than S32205 and S31726 alloys. In the ferric chloride test without crevices, ASTM G48-A, the N08367 alloy withstands pitting at 62 C (145 F). There is a good correlation between the ferric chloride test results and the calculated value of the PREN for the various alloys. Test data for N08367 alloy exposed to 24,000 ppm chloride water with temperature varied from 43 C (110 F) to 71 C (160 F) and ph varied from 4 to 0.5 with H2SO4 are presented in Table 3. No corrosion was observed at ph 4 or 2. With ph adjusted to 1.0, corrosion was not observed up to and including 66 C (150 F). However, at 71 C (160 F) crevice corrosion was observed. With ph 0.5, no corrosion was observed at 60 C (140 F) but crevice attack was observed at 66 C (150 F). The strong influence of the temperature on corrosion rate should be noted. Crevice corrosion data for exposure to a severe acid-chloride solution, the Green Death solution, are given in Table 4. This test is commonly used to compare materials in reducing environments, such as that of the inlet duct of an absorber. Crevice corrosion is observed on S31603 and S31703 at room temperature. At 50 C (122 F) alloys with up to 4.4Mo are corroded. The N08367 (6.2Mo) alloy and higher Mo nickel-base materials resist attack. Further increase in temperature to 70 C (158 F) resulted in significant crevice corrosion on all alloys through the 9Mo N06625 alloy. The 16Mo N10276 alloy exhibited only superficial crevice corrosion. Testing has also been performed under actual service conditions at various locations. Field testing data was presented in 2000 (14). Again, a generic 6 Mo sample was used in the testing. The testing above indicates that N08367 alloy is expected to perform similarly. The most severe test conditions were found at the Orlando Utilities Stanton Energy Plant. Various samples were exposed for 270 days. The slurry average chloride content was ~70,000 ppm, the ph was 5.6, and the temperature was ~130 F (54 C). Figure 4 shows the alloy samples after testing. Note the 6 Mo and N10276 displayed very good corrosion resistance. Crevice corrosion on a S31603 specimen was severe. Localized attack incurred by the S31726 stainless steel was considerably less than that suffered by S31603 stainless steel, but nevertheless still quite severe. One of the duplex stainless steel specimens exhibited under-scale type etching. The results demonstrate the superior resistance of the 6Mo stainless steels to the FGD environment compared to the lower alloyed stainless steels.

10 Table 3: 24,000ppm Chloride Water with ph and Temperature Varied (1) Temperature Weight Loss, g/cm 2 (2) F ( C) ph 0.5 (3) ph 1 ph 2 ph (43) (49) (54) (60) (66) (71) (1) 30 day tests, procedures per ASTM G 48-B (2) Average of two tests (3) ph adjusted with H 2 SO 4 Table 4: Crevice Corrosion Testing in Simulated Scrubber Environment (Green Death (1)) Weight Loss g/cm 2 (2) Alloy 75 F (25 C) 122 F (50 C) 158 F (70 C) S S N N N (1) 7 Vol. % H 2 SO 4, 3 Vol. % HCl, 1 Wt. % CuCl 2, 1 Wt. % FeCl 3 (2) Tests per ASTM G48-b procedures, 72 hour duration

11 Figure 4. Results of exposure to ~70,000 ppm chlorides at a ph of 5.6 and a temperature of ~130F (54C) for 270 days. Exposure to slurry at Orlando Utilities Stanton Energy Center (FL) S32760 Laboratory Testing There is obvious concern that alloys for use in FGD scrubber systems may suffer from crevice corrosion, as crevices abound in all commercial designs. Early laboratory tests (15) were conducted in simple sulphate/ chloride solutions and the results suggested that ph had little effect on the critical crevice corrosion temperature (CCCT). However, more recent work by Weir Materials & Foundries (16) in more realistic slurries has shown that ph has a strong effect and the CCCT can decrease over 20 C as the ph decreases from ph 5 to ph 3. During normal operation ph levels are generally from 4.5 to 6, but under adverse conditions ph values as low as 4 are possible. Hence, WM&F has carried out a series of electrochemical tests in simulated FGD slurries at this ph. Table 5 shows the results of CCCT tests in simulated anthracite slurry at ph of 4. In this environment normal operating temperatures are about 122 F (50 C). The results show that wrought S32760 is superior to the older cast 25Cr duplex. Welded and cast S32760 and J93380 (cast version of ZERON 100) are also suitable in this application. Table 6 shows the CCCT data for simulated lignite slurry, where operating temperatures are typically F (60 65 C). These results show that both cast and welded ZERON 100 are suitable, but the older 25Cr duplex alloy is not. They also show the excellent resistance of ZERON 100 to crevice corrosion, particularly the wrought product. Erosion corrosion can be a significant problem in FGD systems, especially in areas in direct contact with the slurry. These areas include the absorber sump, slurry piping, pumps, valves, and agitators. The calcium sulphate and limestone in FGD slurries are not particularly erosive. It has been found that fly ash causes most of the erosion.

12 Table 5: Critical crevice temperature for some stainless steels in simulated anthracite FGD slurry at ph of 4 Form Alloy CCCT F ( C) Wrought S32760 > 176 (80) Wrought S (64.7) Welded S (58.5) Cast J (57.8) Cast 25Cr Duplex (42) Slurry composition CaSO 4 10 wt. % Chloride 40,000ppm Fluoride 50ppm Dithionate 200ppm Fe 3+ 10ppm A13+ 30ppm Table 6: Critical crevice temperature for some stainless steels in simulated lignite FGD slurry at ph of 4 Form Alloy CCCT F ( C) Wrought S32760 > 181 (83) Wrought S (66.7) Welded S (63.4) Cast J (62.6) Cast S (39.6) Slurry composition CaSO 4 10 wt. % Chloride 15,000ppm Fluoride 200ppm Dithionate 200ppm Fe 3+ 10ppm A13+ 30ppm

13 Tests have been conducted in simulated FGD brines including fly ash in a recirculating erosion test rig (17). Results from pin erosion tests showed that S32760 offered superior erosion resistance to austenitic alloys such as 316L as well as more highly alloyed materials. Figure 6 shows the erosion resistance of several alloys including Z100 as a function of ph. It can be seen that Z100 has the best erosion resistance, which is not affected by ph i.e. the alloy does not corrode significantly at low ph. Applications Figure 5. Pin erosion rig test results in a simulated FGD slurry Both N08367 and S32760 have been used successfully for over 20 years in several areas on the FGD system around the world. Below are highlights of many of the successful applications where these two alloys have been used over the years. N08367 Applications The following section gives several examples of the application of N08367 in actual pollution control applications. Northern Indiana Public Service Company (NIPSCO) Bailly Generating Station. This station uses 2 to 4.5% sulfur bituminous coal. Pure Air on the Lake manages this FGD system. N08367 alloy has been used in several applications in this system. The successful performance of N08367 alloy in earlier applications has led to its utilization in other areas. Estimated conditions of the absorber are ~11,000 ppm chlorides, ph of 6, and 125 F (52 C).

14 Original construction consisting of N08367 alloy recirculation piping, spray piping system, and rotary sparger unit (submerged in the limestone scrubber tank) have been in service for over 16 years. See Figures 5 & 6. In 1997, N alloy w as fabricated into top hats to protect flanged connections in rubber lined steel pipe for slurry pipe headers and the spray piping systems. Top hats w ere also installed in other areas in more recent times. See Figure 7. In 2003, N alloy box beams replaced rubber coated carbon steel beams. These beams, located in the absorber tower, support a 28,000 piece grid packing system. See Figures Figure 5 & 6. N08367 Alloy Rotary Sparger (left), N08367 Alloy Spray Piping (right) Figure 7. N08367 Alloy Top Hats

15 Figure 8 & 9. N08376 Alloy Box Beams (left) replaced rubber coated steel beams (right) Figure 10. N08376 Alloy Box Beams Installed Louisville Gas & Electric (LG&E) Cane Run Station. This station burns 3.5% sulfur coal. N08367 has been used in several applications in this system. The estimated chloride levels in the Unit #6 absorbers are ~5500 ppm. Unit #5 absorber is ~800ppm. In 1990, N alloy replaced S31726 lining in two FGD downcomer ducts. See Figure 11. The S31726 liner failed in less than 3 years due to perforation from pitting. 14ga and 16ga sheet w as used to w allpaper the duct. The N alloy is still in service after 21 years. In 1999, N alloy replaced a 16 coated carbon steel pipe for the pump suction system used to recirculate the scrubber liquor that quenches the flue gas in the absorber tower. The carbon steel supporting beams that support the absorber trays w ere w allpapered w ith N alloy.

16 In 2003, N alloy w as fabricated into liquid distribution rings in the absorber tow er. These w ere installed to protect the absorber tow er w alls. Figure 11. N08376 Alloy used in Absorber Tower and Downcomer Duct Korea Electric Power Company (KEPCO) Taean Units 1-4, Hadong Units 1-6. A total of 10 absorbers were installed for KEPCO, with start-up of eight units in 1998 and two in No problems have been reported since the installation. Each of the 10 wet limestone absorber towers was 16.8m (55 ft.) in diameter and serviced a 500MW boiler. N08367 alloy was used for absorber tower plates, internals including stiffeners and structurals, piping systems, and the absorber trays. Inlet SO 2 concentration was 645 ppm and chloride levels were ~20,000 ppm maximum. The N08367 alloy for this project was produced to a minimum PREN of 47.5 in order to meet the demanding requirements for corrosion resistance. One of the absorber towers may be seen in Figure 12. Figure 12. N08376 Alloy used in Absorber Tower at KEPCO Hadong Power Station

17 Indianapolis Power & Light (IP&L) Petersburg Station. N08367 alloy was used for the wallpapering of a carbon steel duct connecting the electrostatic precipitator to the flue stack. Lower than expected temperatures led to condensation in the bottom of the 12 foot (3.7m) wide duct. The duct was approximately 150 feet (45.7m) long. 35,000 pounds (15,909 kg) of 14ga N08367 alloy sheet were supplied to wallpaper the bottom of the duct to protect against corrosion by the condensate which would include sulfurous acid and chlorides. Gas estimates through the duct were 33 lbs/hour of Cl- and 29 lbs/hr of SO2. The lining and duct are shown in Figure 13. After 5 years in service the duct was removed from service with no reported problems. Reason for removal was the installation of the of a wet FGD system. Due to the success of N08367 in this application, it was selected for portions of the absorber tower contacted after the quench section. Figure 13. N08376 Alloy used for Duct Lining at IP&L Ameren Energy Generating Company Newton Station. N08367 alloy was fabricated into a turning vane for a flue gas stack. The turning vane was installed to address an undesirable cyclone effect at the base of the flue gas stack. Excellent resistance to pitting and crevice attack was demonstrated by the N08367 alloy, necessary for this plant which burns high sulfur coal. The N08367 alloy was chosen based on corrosion testing. The scrubber was decommissioned in 1994, but CIPS (operator at the time) reported that the N08367 performed well in resisting corrosion over several years of service. The vane can be seen in Figure 14.

18 Figure 14. N08376 Alloy used for turning vane Duke Energy Zimmer Station. N08367 alloy 14ga sheet was chosen to line six bypass ducts for each of the absorber modules. The carbon steel bypass ducts were corroding due to the condensation of acid. Installation was performed in early A photo of the duct may be seen in Figure 15. Figure 15. N08376 Alloy used to line bypass ducting

19 New Brunswick Power Coleson Cove Power Plant. Over 14,000 feet (4267m) of N08367 box beams were furnished for use in a wet electrostatic precipitator (WESP). These beams were drawn to an overall size of 1.0 x 6.0 x (25.4mm x 152mm x 3.2mm) average wall for the application. Over 300,000 lbs (136,364 kg) of N08367 alloy sheet was also supplied for use as collector plates, which were hung from the box beams. Over 42,000 lugs were also fabricated from plate. The schematic of this WESP can be seen in Figure 16 below. Figure 16. N08376 Alloy used for collector plates, box beams, and lug clips Westar Energy Jeffrey Energy Center. Westar Energy used over 500 ton of N08367 plate to upgrade their FGD units in N08367 was chosen due to its track record in similar FGD environments. The alloy was mainly used for ductwork to connect the three existing FGD units as well as for modifications to the FGD units in order to increase the SO 2 removal rate to 95%. N10276 was also used in these modifications and new installations where environments were more severe and required a higher corrosion resistant alloy. A section of this ducting can be seen below in Figure 17.

20 Figure 17. N08376 Alloy used for ductwork connecting existing FGD units San Miguel Electric Cooperative. San Miguel Electric has used the N08367 alloy in few areas within their FGD System. Over 5 years ago, they tested both S32205 and N08367for turning vanes in their ductwork. After inspection, they noticed that both the S32205 and AL-6XN looked brand new after several months in service. N08367was also selected for the walls and ceiling of the outlet ducting downstream of the reheater where acid concentration are higher. N08367was also used in some areas on the floor of the ducting along with N It was noticed that where the acids pool on the floor, the N08367did not hold up as well as the N10276, but on the walls and ceiling where the acids could run down the walls, N08367has held up great for nearly 5 years now. Hoosier Energy Merom Station. Hoosier Energy has relined their FGD absorbers with N The original FGD s were constructed from a lower corrosion resistant alloy and after detecting some corrosion, it was determined to reline all of the absorbers using N08367.

21 S32760 Applications The following section gives several examples of the application of S32760 in actual pollution control applications. The excellent corrosion resistance of S32760 combined with its high strength makes it suitable for a wide range of applications in FGD plants. Cast ZERON 100 can be used for pumps, valves, and agitators, while the wrought product can be used for ducting, where acid condensation may occur, up to 300 C. Other applications include gas distribution plates, sprinkler heads, fasteners, centrifuges, and absorber towers. With absorber towers, the high strength of super duplex stainless steel means it is more economic to make absorber vessels from solid alloy rather than clad steel. One power station in the USA has changed from clad to solid super duplex for absorber vessels because of the economics. Ratcliffe Power Station - UK. The slurry centrifuges at Ratcliffe FGD plant were supplied in S32760 in After fifteen years operation, they are in excellent condition. After a short time of operation, the GRP slurry return lines at Ratcliffe FGD plant were suffering severe erosion. These have now been replaced with spools of S32760 and have given no further problems. A picture of the S32760 centrifuges at Ratcliffe can be seen in Figure 19. Figure 19. S32760 slurry centrifuge at Ratcliffe Power Plant Drax Power Station - UK. S32760 has been used successfully for the slurry pumps, agitator stools and gas distribution plates at the Drax FGD plant in the UK since A picture of the FGD slurry recirluation pumps at Drax can be seen in Figure 20. The pumps are lasting 30,000 to 40,000 hours between major overhauls. ZERON 100 has also had the advantage that minor damage can be weld repaired, while white cast irons, also used for FGD pumps, cannot.

22 Figure 20. S32760 slurry recirculation pump fitted at Drax FGD Plant in the UK Power Plant in Texas. S32760 was selected for the fabrication of three FGD outlet duct dampers for a power plant in the state of Texas. The fabricator worked with Rolled Alloys to learn to weld and form the ZERON 100, which was a new alloy to the fabricator. The strength and cost savings vs a higher nickel alloy was the criteria used for material selection as well as it proven corrosion resistance in testing and in FGD environments. Figure 21. S32760 used for three FGD outlet duct dampers at a Texas power plant

23 Summary Alloys N08367 and S32760 are currently being successfully used for many applications in FGD systems. These include absorber bodies, ducting, mixers, spargers, spray piping, turning vanes, dampers, wallpaper lining, reheaters, spray absorbers, structural supports, agitators, and centrifuges. These two alloys have been employed for over 20 years and have demonstrated excellent performance. N08367 and S32760 alloys are shown to be cost effective materials of construction to fill the gap between the 300 series stainless steels and duplex S32205 and the higher molybdenum and nickel based alloys. Both materials are available in a wide variety of product forms (plate, sheet, round bar, pipe, fittings, and flanges) needed to meet the requirements of all FGD system components.

24 References 1. R. J. Brigham, Corrosion, 28 (5), (1972), p R. J. Brigham, E. W. Tozer, Corrosion, 29 (1), (1973), p R. J. Brigham, E. W. Tozer, Corrosion, 30 (5), (1974), p H. E. Deverell, J.R. Maurer, Materials Performance, 17, (3), (1978), p J. R. Kearns, J. Mater. Energy Sys., 7 (1), (1985) p R. Bandy, Y. C. Lu, R. C. Newman, C. R. Clayton, Proc. Equilibrium Diagrams and Localized Corrosion Symposium, P. Frankenthal and J. Kruger, Eds., (Electrochem. Soc., Pennington, NJ, 1984) p J. E. Truman, M. J. Coleman, K. R. Pirt, Brit. Corrosion J., 12 (4), 1977, p H. E. Deverell, J. R. Maurer, Materials Performance, 17, (3), A. H. Tuthill, Materials Performance, 27, (7), H. E. Deverell, C. R. Finn, G. E. Moller, Corrosion/88, Paper No. 313, (Houston, TX: NACE, 1988). 10. A. E. Baumel, M. Horn, H. Grafen, Proc. Fifth International Congress Metall. Corrosion, (NACE, Houston, TX, 1974), p H. Their, A. Baumel, E. Schmidtmann, Archiv. Eisenhutt, 40 (4), (1969), p I. A. Franson, Joint ASME/IEEE Power Gen Conf., 85-JPGC-Pwr-15, (Milwaukee, WI, October, 1985). 13. I. A. Franson, J. R. Maurer, Joint ASME/IEEE Power Gen Conf., 87-JPGC-Pwr-27, (Miami, FL, October, 1987). 14. J. F. Grubb, Proc. of the Mega Symposium, NACE, J P Audouard, P Soulignac and F Dupoiron, Materials Selection for Wet FGD Systems, Presented at "Airpol '90", Louisville, USA Oct 1990.

25 16. R Francis, WM&F Technical Note TN 1235 February J T Dallas and T A McConnell, "Solids Pumping" Seminar, I Mech E London, UK Oct C Stinner, J Wilson, AIRPOL 2007 Conference Proceedings AL-6XN is a registered trademark of ATI Technologies ZERON is a registered trademark of Rolled Alloys