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  • ADVANCED EROSION PROTECTION TECHNOLOGY FOR STEAM BOILER SUPERHEAT, REHEAT AND EVAPORATOR TUBES

    Click here to learn more about Conforma Clad Wear Solutions

  • Chris HarleySenior Applications Engineer

    Conforma Clad Inc.

    Andrew McGee, P.E.EPRI RRAC

    Richard J. StangaroneTennessee Valley Authority

    System EngineerCombustion Process

    Mike Palmer American Electric Power Company

    Philip Sporn Generating Station

    ADVANCED EROSION PROTECTION TECHNOLOGY FOR STEAM BOILER SUPERHEAT, REHEAT AND EVAPORATOR TUBES

  • Introduction

    Electric Power Institute has generated an in-depth report titled TubeRepair 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 G76Tube Repair and Protection from Damage Caused by Sootblower Erosion 10080837 March 2004.

    Test Conditions: Particle Velocity - 141.2 ft/s (40m/s) Temperatures - 9000F (4820C) 11000F (5930C) Impact Angles - 300 , 900

    Test Duration - 3 hours Erodent - Bed ash

    556 - microns Tests focused on elevated temperature solid-

    particle erosion under generally oxidizing conditions.

    Thickness loss reporting

    High PressureRegulator

    Low PressureRegulator

    Variable FeedControl

    MixingChamber

    AccelerationTube

    Sample

    ErosionChamber

    DustCollector

    Mass Flow(orifice plate)

    WaterManometer

    HighPressureAir In

    ParticleFeed

    Dryer

  • High Temperature Test Results - Table

    * indicates coating worn through

    825*226752*18712. Duocor coating9790657611. SA387 steel8574657110. 309L Stainless steel 747064679. 312 Stainless steel947358668. Nickel alloy 72836862657. Nickel alloy 52847572636. Nickel apply 602CA 1047154565. Nickel alloy 622907451544. Nickel alloy 625992528203. LMC-M+WC coating56132362. Wc200 cladding

    38111951. Cr3C2 - NiCr coating900300900300

    At 11000F (5930C)At 9000F (4820C)No. Target MaterialThickness loss

  • High Temperature Test Results - Chart

    EROSION TEST RESULTS

    0

    20

    40

    60

    80

    100

    120

    1. Cr

    3C2 -

    NiC

    r coa

    ting

    2. W

    c200

    clad

    ding

    3. LM

    C-M+

    WC

    coati

    ng4.

    Nick

    el all

    oy 62

    55.

    Nick

    el all

    oy 62

    2

    6. Ni

    ckel

    apply

    602C

    A 7.

    Nick

    el all

    oy 52

    8. Ni

    ckel

    alloy

    72

    9. 31

    2 Stai

    nless

    stee

    l

    10. 3

    09L S

    tainle

    ss st

    eel

    11. S

    A387

    stee

    l

    T

    h

    i

    c

    k

    n

    e

    s

    s

    L

    o

    s

    s

    (

    m

    i

    c

    r

    o

    n

    s

    )

    900F @30 degrees

    900F @90 degrees

    1100F @30 degrees

    1100F @90 degrees

  • 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 Institutes technical report - Tube Repair and Protection from Damage Caused by Sootblower Erosion 10080837 March 2004.

  • Field Test 1 Tennessee Valley Authority, Shawnee Fossil Plant7900 Metropolis Lake RoadPaducah, 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 14500F to 16000F 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

    * Material loss measured 1.5" x .750 area directly in-line with nozzle.

    .0018".0342"6-Apr

    .0012"*.0348"5-Sep

    NA.036"5-Apr

    NA.036" 4-Nov

    as supplied.036" 3-Nov

    Material LossThicknessDate

    Evaporator 2 Tube inspections Conforma Clad

  • 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 StationRoute 33 WestNew 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

    Insp