Click here to learn more about Conforma Clad Wear Solutions ADVANCED EROSION PROTECTION TECHNOLOGY FOR STEAM BOILER SUPERHEAT, REHEAT AND EVAPORATOR TUBES
ADVANCED EROSION PROTECTION TECHNOLOGY FOR STEAM BOILER SUPERHEAT, REHEAT AND EVAPORATOR TUBES Chris Harley Senior Applications Engineer Conforma Clad Inc. Andrew McGee, P.E. EPRI RRAC Richard J. Stangarone Tennessee Valley Authority System Engineer Combustion Process Mike Palmer American Electric Power Company Philip Sporn Generating Station
Introduction Electric Power Institute has generated an in-depth report titled Tube Repair and Protection from Damage Caused by Sootblower Erosion 10080837 March 2004 which will be summarized in the following pages. The focus of this paper is to qualify by actual field tests the hot erosion lab tests conducted in actual highly erosive boiler environment.
Background Boiler tube failures continue to be the number one cause of forced outages in fossil plants today responsible for an estimated 6% loss of unit availability. 23% of the total tube failures reported were due to either soot blower or flyash erosion. Extending time between major outages two, four, and even five years is resulting in increased forced outages due to tube failures. An estimated seventeen causes of tube leaks have been sited in the 217 plants polled. However, one of the most problematic, hardest to predict and seemingly increasing is erosion caused failures.
Tube Problems - Failures Weld overlay pad welding Stainless steel tube shields
Erosion. Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and the impinging solid particles Annual Book of ASTM Standards, Wear and Erosion: Metal Corrosion If high erosion-resistant particles exist in low erosion resistant or soft matrix, the impacting particles can undercut and remove portions of the material (Figure 1). However, if the high erosion resistant particles such as Tungsten carbide are densely packed in a matrix material that causes the impacting particles to impinge on a greater percent of the hard particle, the erosion resistance increases dramatically (Figure 2). Fig 1 Fig 2
Materials Tested SA387 Grade 11 alloy steel 309L stainless steel GTAW Nickel alloy 52 GMAW Nickel alloy 72 GTAW Nickel alloy 622 GMAW Nickel alloy 625 GMAW Nickel alloy 602CA GMAW 312 stainless steel GMAW WC200 braze alloy infiltration brazed Cr3C-NiCr coating HVOF Duocor coating TWAS LMC-M WC blend coating HVOF The base material for all test samples was SA387 grade 11 alloy.
Erosion Testing ASTM G76 Tube Repair and Protection from Damage Caused by Sootblower Erosion 10080837 March 2004. High Pressure Regulator Low Pressure Regulator Variable Feed Control Particle Feed Mass Flow (orifice plate) Erosion Chamber Test Conditions: Particle Velocity - 141.2 ft/s (40m/s) Temperatures - 900 0 F (482 0 C) 1100 0 F (593 0 C) Impact Angles - 30 0, 90 0 High Pressure Air In Dryer Mixing Chamber Sample Acceleration Tube Test Duration - 3 hours Erodent - Bed ash 556 - microns Tests focused on elevated temperature solidparticle erosion under generally oxidizing conditions. Dust Collector Water Manometer Thickness loss reporting
High Temperature Test Results - Table Thickness loss At 1100 0 F (593 0 C) No. Target Material At 900 0 F (482 0 C) 30 0 90 0 30 0 90 0 1. Cr 3 C 2 - NiCr coating 5 19 11 38 2. Wc200 cladding 6 23 13 56 3. LMC-M+WC coating 20 28 25 99 4. Nickel alloy 625 54 51 74 90 5. Nickel alloy 622 56 54 71 104 6. Nickel apply 602CA 63 72 75 84 7. Nickel alloy 52 65 62 68 83 8. Nickel alloy 72 66 58 73 94 9. 312 Stainless steel 67 64 70 74 10. 309L Stainless steel 71 65 74 85 11. SA387 steel 76 65 90 97 12. Duocor coating 187 752* 226 825* * indicates coating worn through
High Temperature Test Results - Chart EROSION TEST RESULTS 120 100 80 60 40 20 0 900F @30 degrees 900F @90 degrees 1100F @30 degrees 1100F @90 degrees 11. SA387 steel Thickness Loss (microns) 1. Cr3C2 - NiCr coating 2. Wc200 cladding 3. LMC-M+WC coating 4. Nickel alloy 625 5. Nickel alloy 622 6. Nickel apply 602CA 7. Nickel alloy 52 8. Nickel alloy 72 9. 312 Stainless steel 10. 309L Stainless steel
High Temperature Test Results - Summary Among the twelve alloys tested, the materials with the highest density of erosion-resistant particles i.e., Tungsten carbide and Chrome carbide showed the highest erosion resistance. The Cr3C2-NiCr HVOF applied coating showed the highest erosion resistance followed closely be the infiltration brazed WC200 material both with erosion resistant particle percentages close to 70%. Due to the environmental factors such as thermal shock, erosion resistant material bond strengths, as well as many others come into play. The following field tests will compare the laboratory qualified high density erosion resistant particle materials to other industry accepted methods of erosion protection. Additional detailed information regarding the summarized lab test can be found in Electric Power Institute s technical report - Tube Repair and Protection from Damage Caused by Sootblower Erosion 10080837 March 2004.
Field Test 1 Tennessee Valley Authority, Shawnee Fossil Plant 7900 Metropolis Lake Road Paducah, KY 42086 Unit 10 atmospheric bubbling fluidized bed 3 evaporator sections in the boiler fed in parallel from the boiler feed pumps In-bed tubes are submerged in a mixture of coal, limestone and recycled ash Temperatures 1450 0 F to 1600 0 F Evaporator tubes were 2.25 OD x.220 SA178C rifled tubes.
Erosion History New installation wear protection was Extendalloy Spray and fuse 45% Tungsten Carbide in a NiCr matrix. From December 1988 October 1991 the maximum erosion rates ranged from.001 -.002 /1000 hours near the recycle feed nozzles 1992 changes in fuel and operating conditions increased tube erosion resulting in numerous failures.
Erosion History 1996 tubes leaks had become a serious problem resulting in replacements of tubes in evaporator 2 and half of evaporator 1. 1999 all evaporators replaced protected with Extendalloy coated 360 degrees During 1999-2000 outage test tubes were installed for evaluations Stoody 140 weld overlay, NiCr-3 and NiCrMo-3 HVOF, 312 and 309 stainless steel weld overlay, and a Chrome carbide weld overlay. 2002 all test tubes removed do to heavy erosion and leaks 2002 Conforma Clad infiltration brazed 70% tungsten carbide protected tubes installed for tests
Continued Testing Results Evaporator 2 Tube inspections Conforma Clad Date 3-Nov 4-Nov 5-Apr 5-Sep 6-Apr Thickness.036".036".036".0348".0342" Material Loss as supplied NA NA.0012"*.0018" * Material loss measured 1.5" x.750 area directly in-line with nozzle.
Field Test 1 Tennessee Valley Authority, Shawnee Fossil Plant - Summary High erosion resistant particles densely packed in a matrix material has a measured life extrapolation of 15 years Additional factors were thought by Tennessee Valley Authority engineering to play a role in the success or failure of erosion resistant coatings. Material bond strengths to the base substrate were thought to play a role in the failure of the spray method coatings. Bond strengths of only approximately 40MPa for the spray methods vs. the bond strength of the infiltration brazing process at 483MPa were unable to withstand thermal cycling along with the simple handling and installations. Due to the low erosion rate of the Conforma Clad cladding over the past 29 months, and the extrapolated life resulting from these tests, Tennessee Valley Authority will be replacing all 3 sections of the evaporator with this Conforma Clad infiltration brazed cladding in the scheduled 2007 outage.
Field Test 2 American Electric Power, Philip Sporn Generating Station Route 33 West New Haven, West Virginia 25265 Unit 1 Babcock and Wilcox front fired 153MW boiler. Bituminous coal supplied to the boiler by five B&W EL 70 pulverizers. Super heat tubes legs 2.750 x 2.80 SA210 grade 1A S shape 60 long. Area flue gas temperature 700 degrees F. Steam condition 2450 PSI, 550 degrees F.
Erosion History: High velocity fly ash entrained flue gas. Erosive attack accelerated by increased fly ash concentration during periods of soot blowing. Tubes previously protected with shields. Area tubes and legs requiring pad weld repair every 2 4 years. Major rebuild Spring 2004 Superheat tube legs protected 2000 on the flow side with infiltration brazed high erosion resistant particle Conforma Clad material - figure 3 Fig 3
Unit 1 superheater tube inspections Plant applied approx. 8 of a trowel applied ceramic in the high erosion area for added erosion protection. Figure 4 Inspections performed March 2006 after 3 years run time. Visual inspection of the high erosion areas along with eddy current measurements of infiltration brazed cladding. Figure 5 All trowel applied ceramic was eroded away. No measurable loss of the infiltration brazed cladding. Figure 4 Figure 5
Field Test 2 American Electric Power, Philip Sporn Generating Station Due to undetermined exposure of the infiltration brazed material to the erosive environment, the test results were to some degree inconclusive. However, referring back to the statement that if high erosion-resistant particles, in this case Alumina, exist in low erosion resistant or soft matrix, the impacting particles can undercut and remove portions of the material. This would explain the high volume loss of the trowel in ceramic. Arrangement are in place to continue monitoring this application. In addition, numerous other installations around the United States, Germany, Poland, South Africa, India, China and the Czech Republic are being monitored and will be reported as the information becomes avalible.
Conclusion While erosion caused failures are only one of the many reasons for tube failures the proper selection of a protective material is critical to successful outage avoidance. Returns on the initial investment of preventative maintenance programs involving high erosion prone boiler tubes can have a payback in as little as one forced outage avoidance. Utilizing today s modern erosion and corrosion technologies for boiler tube protection is getting plants one step closer to achieving new outage to outage goals.