recovery boiler superheater tube corrosion and cracking...

Recovery Boiler Superheater TubeCorrosion and Cracking Studies

Jim Keiser, Gorti Sarma, Kim Choudhury and Adam Willoughby -Oak Ridge National Laboratory

Joey Kish, Laurie Frederick and Doug Singbeil - PapricanFrançois Jetté - Domtar Inc

Peter Gorog - Weyerhaeuser Company

7th International Colloquium on Black Liquor Combustion and Gasification

July 31-August 2, 2006; Jyväskylä, Finland

2BLG Colloquium, SH, August 2006 Finland

The DOE Funded Project “Materials For Industrial Heat Recovery Systems” Has Addressed Several Topics

Recuperators on aluminum melting furnaces

Primary air port cracking

Mid-furnace corrosion

Superheater tube corrosion and cracking


Our Study Of Degradation Of Superheater Materials Includes A Number Of Tasks

Examination of cracked or corroded superheater tubes

Industry survey of experience with carbon steel and alternate superheater tube materials

Study of mechanical cycling and temperature of superheater tubes

Laboratory corrosion studies of alternate superheater materials

Exposure of superheater corrosion probes with alternate materials


Potential Benefits From Study Of Superheater Tube Materials

Operation of recovery boilers at higher steam temperatures and pressures offers the potential for more efficient operation

To achieve the potential efficiency benefits, structural materials must have sufficient corrosion resistance for the environments they will encounter

This study should provide clear, objective data on the corrosion resistance of candidate alloys to expected HP/HT boiler superheater environments

From the information collected it should be possible to make materials recommendations for superheater sections as a function of temperature


During A Shutdown, Fourteen Tube Sections Were Removed From The Intermediate Superheater For Examination

Fig 16

The tube sections removed included the weld attaching the tube to the load-bearing member.


The Superheater Tubes Of Interest Were In The Intermediate Bank On The Right Side Of The Boiler

1/2 19/2

13/14

17/18

15/16

7/8 23/2

11/12

9/10

5/6

3/4

21/2

ScreenTubes

SuperheaterBanks

Roof

Instrument Box

Sootblower


The Tubes Were Thoroughly Examined To See If There Was Any Evidence Of Cracking

The remnants of the high crown seal box were ground off the tubes without removing any of the tube material

A dye penetrant examination was conducted on each of the tubes – no crack indications were found

A magnetic particle inspection was conducted on a few of the tubes - no crack indications were found

Cross sections were cut from each of the tubes at the 3, 6, 9 and 12 o’clock positions just below the tube to crown weld

The cross sections were examined microscopically in the as-polished and etched conditions


Cracks Were Found In The 3 And 9 O’clock Positions On The Tube From Platen 8

One crack advanced about 20% of the way through the tube wall.


Cracks Were Also Found In The First Tube From Platens 11 and 12

Both cracks were associated with the weld.


The Second Tube In Platen 14 Was Cracked

Crack originated in the heat affected zone and advanced about 20% through the tube wall.


Two Failed Tubes, Found During The Hydro Following The Fall, 2004 Shutdown, Have Also Been Examined

These tubes were from the opposite side of the superheater platens from where several previous failures had occurred

Welds attaching the tubes to the support were ground off then a dye penetrant test was done

Dye penetrant examinations revealed large cracks

Cross sections of the tubes were examined metallographically

Fig 10


Cracks On These Tubes Followed The Weld HAZ Along The Tube To High Crown Seal Weld

The through-wall cracks appear to follow the bottom of the weld of the

tube to the high crown seal box.


Cross Sections Of The Tubes Show Through Wall Cracks In The HAZ With Secondary Cracking


To Study The Cyclic Stresses, Strain Gauges Were Installed In October, 2003 On The First Tube Of Two Platens

Three strain gauges were installed on each tube

The strain gauges were 120° apart at 6, 10 and 2 o’clock

The strain gauges are rated for service up to 750°C

A data point is collected from each strain gauge once per second

A thermocouple was also installed on each tube

Fig 22


The Tubes Were Installed So The Strain Gauges Were Just Below The Tube To High Crown Seal Weld

Photos showing the installation of superheater tube with strain gauges. In the picture on the left, the #2 tube has been installed in platen 14, but the hole is still empty where tube #1 with the strain gauges will be installed. In the center photo, the #1 tube with strain gauges is in position, and in the picture on the right, the tube is welded in place and the strain gauge and thermocouple wires extend through a specially made opening.


The Strain Gauge Data For A Typical Day Of Operation Shows Intermittent Periods Of Activity

Strain gauge data for a typical day of “clean” boiler operation. The strain associated with the largest of the oscillations is not sufficient to initiate fatigue cracks. However, these oscillations could promote growth of existing cracks.

-400

-350

-300

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-150

-100

-50

0

7:30 8:00 8:30 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00

time

stra

in

Tube 4 SG1

Tube 4 SG2

Tube 4 SG3

Tube 14 SG1

Tube 14 SG2

Tube 14 SG3

Tube 5 SG1

Tube 5 SG2

Tube 5 SG3


Plotting The Data Over A Shorter Period Reveals A Swinging Motion Is Caused By The Sootblowers

Five sootblower cycles are shown, note the activity induced by each sootblower begins on platen 5 then moves to platen 14 then back to platen 5.

Ashdown 2 Strain Gauges May 17, 2004

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-350

-300

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-200

-150

-100

-50

0

8:19 8:20 8:21 8:22 8:23 8:24 8:25 8:26 8:27 8:28 8:29 8:30 8:31 8:32 8:33 8:34 8:35 8:36 8:37 8:38 8:39

time

Stra

in (M

pa)

Tube 5 SG1 Tube 5 SG2 Tube 5 SG3 Tube 14 SG1 Tube 14 SG2 Tube 14 SG3


This Superheater Has A Plugging Problem And The Extent Of Plugging Is Reflected In The Strain Gauge Activity

Number of cycles (strain changes of at least 20 units) over a three month period showing varying amounts of plugging in the intermediate superheater area.

Ashdown 2 Strain Gauge Daily Total Cycles March -May 2004

0

500

1000

1500

2000

25003/

1/04

3/3/

043/

5/04

3/7/

043/

9/04

3/11

/04

3/13

/04

3/15

/04

3/17

/04

3/19

/04

3/21

/04

3/23

/04

3/25

/04

3/27

/04

3/29

/04

3/31

/04

4/2/

044/

4/04

4/6/

044/

8/04

4/10

/04

4/12

/04

4/14

/04

4/16

/04

4/18

/04

4/20

/04

4/22

/04

4/24

/04

4/26

/04

4/28

/04

4/30

/04

5/2/

045/

4/04

5/6/

045/

8/04

5/10

/04

5/12

/04

5/14

/04

5/16

/04

5/18

/04

5/20

/04

5/22

/04

5/24

/04

5/26

/04

5/28

/04

5/30

/04

No

of C

ycle

s

SG5-1 SG5-2 SG5-3 SG14-1 SG14-2 SG14-3

March 1 April 13 May 18

Ashdown 2 Strain Gauge Daily Total Cycles March -May 2004

0

500

1000

1500

2000

25003/

1/04

3/3/

043/

5/04

3/7/

043/

9/04

3/11

/04

3/13

/04

3/15

/04

3/17

/04

3/19

/04

3/21

/04

3/23

/04

3/25

/04

3/27

/04

3/29

/04

3/31

/04

4/2/

044/

4/04

4/6/

044/

8/04

4/10

/04

4/12

/04

4/14

/04

4/16

/04

4/18

/04

4/20

/04

4/22

/04

4/24

/04

4/26

/04

4/28

/04

4/30

/04

5/2/

045/

4/04

5/6/

045/

8/04

5/10

/04

5/12

/04

5/14

/04

5/16

/04

5/18

/04

5/20

/04

5/22

/04

5/24

/04

5/26

/04

5/28

/04

5/30

/04

No

of C

ycle

s

SG5-1 SG5-2 SG5-3 SG14-1 SG14-2 SG14-3

March 1 April 13 May 18


The Effect Of Plugging Is Clearly Indicated In The 15 Minute Data Plots For The Three Dates

Strain gauge data for 15 minute period on the three dates indicated on the previous slide. Note the suppression of oscillations on April 13 when

the superheater appears to be badly plugged.


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-50

0

2:30 2:31 2:32 2:33 2:34 2:35 2:36 2:37 2:38 2:39 2:40

time

stra

in


Ashdown 2 Strain Gauges April 13, 2004

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-200

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-100

-50

0

1:00 1:01 1:02 1:03 1:04 1:05 1:06 1:07 1:08 1:09 1:10

time

stra

in


Ashdown 2 Strain Gauges March 1, 2004

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-200

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-50

0

1:20 1:21 1:22 1:23 1:24 1:25 1:26 1:27 1:28 1:29 1:30

time

stra

in



-400

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-250

-200

-150

-100

-50

0

2:30 2:31 2:32 2:33 2:34 2:35 2:36 2:37 2:38 2:39 2:40

time

stra

in


Ashdown 2 Strain Gauges April 13, 2004

-400

-350

-300

-250

-200

-150

-100

-50

0

1:00 1:01 1:02 1:03 1:04 1:05 1:06 1:07 1:08 1:09 1:10

time

stra

in


Ashdown 2 Strain Gauges March 1, 2004

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-200

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-50

0

1:20 1:21 1:22 1:23 1:24 1:25 1:26 1:27 1:28 1:29 1:30

time

stra

in


March 1, 2005

April 13, 2005 May 18, 2005


The Daily Averages Of Strain Gauge Measurements Give Some Indication Of Loading On The Tubes

Ashdown 2 Daily Averages per Strain Gauge Jan 2004 to June 2005

-350

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-100

-50

01-

Jan-

04

16-J

an-0

4

31-J

an-0

4

15-F

eb-0

4

1-M

ar-0

4

16-M

ar-0

4

31-M

ar-0

4

15-A

pr-0

4

30-A

pr-0

4

15-M

ay-0

4

30-M

ay-0

4

14-J

un-0

4

29-J

un-0

4

14-J

ul-0

4

29-J

ul-0

4

13-A

ug-0

4

28-A

ug-0

4

12-S

ep-0

4

27-S

ep-0

4

12-O

ct-0

4

27-O

ct-0

4

11-N

ov-0

4

26-N

ov-0

4

11-D

ec-0

4

26-D

ec-0

4

10-J

an-0

5

25-J

an-0

5

9-Fe

b-05

24-F

eb-0

5

11-M

ar-0

5

26-M

ar-0

5

10-A

pr-0

5

25-A

pr-0

5

10-M

ay-0

5

25-M

ay-0

5

T5-1 T5-2 T5-3 T14-1 T14-2 T14-3T = Tube

Ashdown 2 Daily Averages per Strain Gauge Jan 2004 to June 2005

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01-

Jan-

04

16-J

an-0

4

31-J

an-0

4

15-F

eb-0

4

1-M

ar-0

4

16-M

ar-0

4

31-M

ar-0

4

15-A

pr-0

4

30-A

pr-0

4

15-M

ay-0

4

30-M

ay-0

4

14-J

un-0

4

29-J

un-0

4

14-J

ul-0

4

29-J

ul-0

4

13-A

ug-0

4

28-A

ug-0

4

12-S

ep-0

4

27-S

ep-0

4

12-O

ct-0

4

27-O

ct-0

4

11-N

ov-0

4

26-N

ov-0

4

11-D

ec-0

4

26-D

ec-0

4

10-J

an-0

5

25-J

an-0

5

9-Fe

b-05

24-F

eb-0

5

11-M

ar-0

5

26-M

ar-0

5

10-A

pr-0

5

25-A

pr-0

5

10-M

ay-0

5

25-M

ay-0

5

T5-1 T5-2 T5-3 T14-1 T14-2 T14-3T = Tube


Laboratory Corrosion Studies Of Alternate Materials Are Being Conducted At Paprican

Objective– Determine relative corrosion resistance of candidate tube

alloys in simulated HP/HT recovery boiler superheater environments

Approach– Crucible test method using horizontal three-zone furnaces

Variables– Alloy composition (materials); temperature; time


Alternate Materials For Superheater Corrosion Studies (Alloy Sets For Different Test Conditions)

- - -1018Bal.SS 347H

1- - -9Bal.SA213 T91

Low Temperature Alloy Set (A1)

High Temperature Alloy Set (A2)

0 [3.4Al]61295.1Alloy 693

1.53233Bal.Alloy 33

3.53127Bal.Alloy 28

- - -2025Bal.SS 310H

1.53233Bal.Alloy 33

3.53127Bal.Alloy 28

- - -2025Bal.SS 310H

- - -1018Bal.SS 347H

MoNiCrFeAlloy


Salt Deposit Mixture

525

(977)

24.44.98.46.156.2D1

SO4CO3ClKNa

FMT

°C

(°F)

Chemical Composition (wt.%)No.

Simulates typical deposit in coastal/closed-cycle mill

“Worst Case” salt deposit mixture


Salt Deposit Melting BehaviorTe

mpe

ratu

re D

iffer

ence

(°C

/mg)

Temperature (°C)

FMT = 525 °C20 °C/min


FY 2006 Test Matrix

530 °C510 °C336N2D1A1

Influence of Expose Time (Corrosion Kinetics)

N2

Cover

Gas

N2

Cover

Gas

560 °C336D1A2

Furnace

3

Furnace

2

Furnace

1

t

(h)

Salt

Deposit

Alloy

Set

Influence of Temperature

336h168h24h510D1A1

Furnace

3

Furnace

2

Furnace

1

T

(°C)

Salt

Deposit

Alloy

Set


Superheater Corrosion Probe

6 materials and a total of 15 samples, each about 10 cm (4 inches) long and 5 cm (2 inches) OD

Spring loaded to hold samples tightly together

Air cooled

Exposed in location where maximum boiler gas temperature is approximately 650°C (1200°F)

Temperature gradient is expected to be at least 75C°

Plan for 1000 or 1500 h exposure

Probes will be exposed in two mills


Materials Used For Samples Offer A Wide Range Of Composition And Corrosion Resistance

0.5 Ti 1.5 Nb

3.20.02Bal295.4Alloy 693

0.4 N0.011.6313332Alloy 33 weld overlay

1.0 Cu0.023.53127BalAlloy 28

0.5202552310S

0.50.089.517Bal347H

0.22 V0.0130.060.110.950.28.30BalT91

OtherAlNbCMoNiCrFeAlloyNominal compositions in wt %


Schematic Of Superheater Corrosion Probe


All 15 Samples Are Interlocking And Have Two Thermocouples On Each


SummaryCracks developed in superheater tubes in the heat affected zones of welds attaching the tube to the support structure

Strain gauges on the superheater tubes showed amplitude of current tube swinging is not sufficient to cause fatigue cracking

Laboratory corrosion studies of alternate superheater tube materials are being conducted in environments that duplicate current conditions as well as those of a boiler operating at higher steam temperatures and pressures

Air cooled superheater corrosion probes which will expose samples of alternate superheater tube materials are being prepared for exposure in two mills under conditions that simulate the temperature and chemical environment of a boiler operating at higher steam temperatures and pressures

recovery boiler superheater tube corrosion and cracking...

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