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. Cr3

C2 - N

iCr c

oating

2. W

c200

clad

ding

3. LM

C-M+W

C coati

ng4.

Nickel

alloy

625

5. Nick

el all

oy 62

2

6. Nick

el ap

ply 60

2CA

7. Nick

el all

oy 52

8. Nick

el all

oy 72

9. 31

2 Stai

nless

stee

l

10. 3

09L S

tainle

ss st

eel

11. S

A387 s

teel

Thic

knes

s Lo

ss (m

icro

ns)

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 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 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

• 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.