Tappi 2005 Digester Corrosion Information Meeting

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MINUTES

DIGESTER CORROSION INFORMATION MEETING

August 31, 2005 0830 to 1000 a.m. Eastern Time

Room 403 Philadelphia Marriott Hotel

1201 Market Street Philadelphia, PA

1. Welcome and Statement of Antitrust Compliance

The final meeting of the TAPPI Digester Corrosion Task Group was held during the TAPPI Engineering, Pulping, and Environmental Conference in Philadelphia. The meeting was conducted in accordance with TAPPIs Antitrust Policy and Procedures. A list of attendees is attached as Appendix A.

2. Approval of Agenda

The agenda for the August 31 2005 meeting had previously been approved by TAPPI headquarters prior to distribution by email.

3. Approval of Minutes March 21-22, 2005 meeting in Glens Falls NY

The minutes of the March 2005 meeting had previously approved by TAPPI headquarters prior to distribution by email. The minutes were approved by the Task Group without amendment.

4. Discussion Items The presentations during the August 2005 meeting of the Task Group were a retrospective of the activities of the Task Group from its inception in 1980 when it was originally created in the aftermath of the catastrophic failure of the continuous digester at the Pine Hill mill in Alabama. A summary of the highlights of all of the Task Group meetings and activities is attached to these minutes as Appendix B. Copies (as handouts) of the PowerPoint slides used in the presentations are attached as Appendix C.

Minutes of the August 31, 2005 TAPPI Digester Corrosion Task Group Meeting

4.1 Overview of Activities of the TAPPI Digester Cracking and

Corrosion Task Groups Angela Wensley, Angela Wensley Engineering, White Rock, BC Angela Wensley has chaired the Task Group since 1986. During her tenure the focus of the Task Group shifted to include rapid corrosion thinning of digesters, corrosion problems with ancillary vessels, and batch digester corrosion. Meetings were held twice per year - the Spring meetings were expanded to 2 days in an educational format devoted to enhancing the understanding of digester corrosion problems and the available alternatives for protection.

4.2 The Continuous Digester Cracking Task Group 1980-1985 Dave Bennett, Corrosion Probe, West Nyack, NY

Dave Bennett was the original chairman of the task group from 1980 until 1986. Under his leadership, the Task Group issued four reports that were invaluable for the industry in clarifying the mechanism of the cracking, the extent of the problem in the industry, the best methods of nondestructive testing to find the cracks, and recommendations on evaluation and repair of cracks. Dave also chaired the TAPPI/IPC Digester Cracking Research Committee that was formed to investigate the causes of caustic stress corrosion cracking and the methods to prevent it. The DCRC was funded both from digester owner/operators and by Kamyr Inc. Research contracts were awarded to The Institute of Paper Chemistry, Paprican, and Battelle Columbus

4.3 Digester Cracking at Procter and Gamble

Charlie Guzi, Retired, Cincinnati, OH Charlie Guzi was the original secretary of the Task Group. During this time he was employed by Proctor & Gamble whose Grande Prairie AB and Flint River GA mills were used to test out many of the digester cracking preventive measures including sealed thermal spray coating, weld overlay, anodic protection, and stress relief heat treatment. Unfortunately, Charlie was unable to make it to the August 31, 2005 meeting of the task group. His presentation is included in Appendix C.

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4.4 The Digester Cracking Research Committee Sandy Sharp, MeadWestvaco, Laurel, MD

Sandy Sharp was the chairman of the Digester Cracking Research Steering Committee that consisted of:

- Dave Bennett (Packer Engineering) - Dave Bowers (IPC) - Pete Donofrio (Champion Paper) - Carl Elmore (Kamyr Inc.) - Fred Ferrari (Scott Paper) - Charlie Guzi (Proctor & Gamble) - Roger Kilgore (Boise Cascade) - Larry Laliberte (International Paper Co.) - Angela Wensley (MacMillan Bloedel)

Sandy's presentation is included in Appendix C. 4.5 Research into Caustic Stress Corrosion Cracking Doug Singbeil, Paprican, Vancouver BC

Doug Singbeil had presented a paper on caustic stress corrosion cracking of carbon steel in white liquor at the 3rd International Symposium on Corrosion in the Pulp and Paper Industry held only months before the Pine Hill failure. As part of the DCRC research program, Doug and Andy Garner developed a ring-weld specimen to investigate various crack preventive measures. Doug's presentation is included in Appendix C.

4.6 Anodic Protection

Anodic protection was one of the three crack preventive measures ultimately approved by the DCRC.

4.6.1 Ian Munro, P.Eng., Aurora, ON

Ian Munro was employed by Corrosion Service Inc. at the time of the Pine Hill failure. He helped develop some of the first commercial anodic protection systems for digesters and was active in the Task Group from the early days. Ian's presentation is included in Appendix C.

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4.6.2 Winston Shim, Corrosion Service Co, Downsview, ON

Winston Shim was present during the installation of some of the earliest anodic protection systems in continuous digesters, including the system installed in the rebuilt Pine Hill digester in 1985. Winston's presentation is included in Appendix C.

4.6.3 Martti Huttunen, Savcor Consulting, Vancouver, BC

Martti Huttunen has been involved with installations of anodic protection systems in continuous digesters since the late 1980's, and has been an active participant in the Task Group since the late 1980's. Martti's presentation is included in Appendix C.

4.7.1 Panama City Batch Digester Failure Overview Max Moskal, M&M Engineering, Indian Head Park, IL

Max Moskal was with Stone Container Corporation and was active in the early days of the Task Group. He was still with Stone Container at the time of the catastrophic failure of a batch digester at their Panama City, FL, mill in 1994. Max's presentation is included in Appendix C.

4.7.2 Duplex Stainless Steels for Digesters Max Moskal, M&M Engineering, Indian Head Park, IL Stone Container Corporation was one of the first pulp and paper companies in North America to construct new batch digesters using duplex stainless steels. Max Moskal has given several reports on the status of duplex digesters in North America to the Task Group. Max's presentation is included in Appendix C.

4.8 Investigations into Corrosion of Weld Overlay in Batch Digesters

Craig Reid, Bacon Donaldson, Richmond, BC

Craig Reid reviewed the corrosion of batch digesters and in particular their protection using stainless steel weld overlay. Craig has previously given a number of comprehensive presentations to the Task Group on the corrosion of stainless steel weld overlay in batch digesters, first when he was with MacMillan Bloedel, and continuing after he moved to Bacon Donaldson (now Acuren). Craig's ultimate presentation is included in Appendix C.

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4.9 Cracking of Duplex Stainless Steel Bottom Scrapers Margaret Gorog, Weyerhaeuser, Federal Way, WA

Cracking of bottom scrapers is currently the major unresolved materials and corrosion problem in continuous digesters. Weyerhaeuser mills have several bottom scrapers constructed using duplex stainless steel. Some of these have experienced cracking. Margaret's report was an update of a comprehensive presentation that she gave to the Task Group in March 2005. Margaret's presentation is included in Appendix C.

4.10 Summary: What have We Learnt?

Andy Garner, Andrew Garner and Associates, Vancouver, BC Andy Garner was at Paprican when the Pine Hill failure occurred. He directed much of the research into caustic stress corrosion cracking of digesters. He retired as director of the Vancouver laboratory of Paprican in 2004. Andy had given a presentation on the history of the DCRC at the February 2004 meeting of the Task Group. Andy's presentation is included in Appendix C.

5. Other Business

Angela Wensley stepped down after serving for 20 years as the Chairman of the Digester Corrosion Task Group.

6. Next Meeting

No further meetings of the Task Group were planned.

7. Adjournment The meeting was adjourned at 10 a.m. on August 31, 2005. Angela Wensley was - and still is - grateful for the bouquet of flowers from Elisabeth Torsner.

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Appendix A

Attendance Aug. 31, 2005 TAPPI Digester Corrosion Information Meeting NAME COMPANY EMAIL

Dennis Beggs Smurfit-Stone [email protected] Dave Bennett Corrosion Probe Inc. [email protected] Brown Georgia Pacific [email protected] Brown Smurfit-Stone [email protected] Dewayne Carver Alloy Cladding [email protected] Bill Fuller FRM Consulting [email protected] Garner Andrew Garner & Associates [email protected] Gilkey FM Global mark,[email protected] Gorog Weyerhaeuser [email protected] Huttunen Savcor Consulting [email protected] Jiang Andritz [email protected] Johansson INDT [email protected] Kaiser Angela Wensley Engineering [email protected] Lansing M&M Engineering [email protected] Lykins New Page [email protected] MacDonald Alloy Cladding [email protected] Macke GE Inspection Services [email protected] Moskal M&M Engineering [email protected] Nadezhdin Norbord [email protected] Parrish FM Global [email protected] Craig Reid Bacon Donaldson [email protected] Reid INDT [email protected] Sharp MeadWestvaco [email protected] Sherman Corrosion Probe [email protected] Shim Corrosion Service [email protected] Singbeil Paprican [email protected] Svensson Savcor [email protected] Thompson Paprican [email protected] Torsner Outokumpu Stainless [email protected] Wegrelius Outokumpu Stainless [email protected] Wensley Angela Wensley Engineering [email protected]

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Appendix B

ACTIVITIES OF THE TAPPI DIGESTER CORROSION/CRACKING TASK GROUP

September 26, 1980 - Catastrophic failure of the Pine Hill continuous digester. October 29, 1980 - First meeting of the Continuous Digester Cracking Task Group in

Montgomery, AL. - To develop industry guidelines for inspection, repair, and prevention of

weld and/or metal failure in continuous digesters to ensure safe operation on an industry-wide basis.

- A task group of the NDT subcommittee, chaired by John Ridgeway (INDT). - Dave Bennett (Hammermill Paper) appointed Task Group chairman - Larry Lalibert (IP) appointed Task Group vice-chairman - Charlie Guzi (Proctor & Gamble) appointed Task Group secretary.

November 6, 1980 - Second meeting of the Task Group, in Atlanta GA.

- Discussion of NDT techniques - Field reports of digester cracking

December 2, 1980 First Report of the Task Group

- Summary of inspections - Inspection procedures and recommendations - Request for information

December 15, 1980 Second Report of the Task Group

- Findings and recommendations concerning repair of cracks. December, 1980 Third meeting of the task group February 17, 1981 Fourth Meeting of the Task Group

- No minutes extant for either meeting in the Task Group archives April 8, 1981 Fifth meeting of the Task Group, in Toronto ON.

- Report on cracking and numerous through-wall leaks in an impregnation vessel at Zellstoff und Papierfabrik in Frantschach, Austria, between 1978 and 1980.

April 8, 1981 Third Report of the Task Group

- Weld repair of cracks considered a temporary repair. - Post weld heat treatment (PWHT) recommended for new digesters

September 28, 1981 Sixth Meeting of the Task Group, in Atlanta GA.

- Reviewed responses received on digester inspections. February 1, 1982 Seventh Meeting of the Task Group, in Chicago IL.

- Report of re-cracking of welds in the new replacement top section of the Pine Hill continuous digester.

- Report of cracking up to 0.6 inches deep in a fully stress-relieved vessel. - Results of acoustic emission (AE) inspections not good.

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Appendix B

February 18, 1982 Fourth Report of the Task Group - Of 85 vessels in North America that were properly inspected, 22 had cracks,

some in excess of -inch depth March 24, 1982 Eighth Meeting of the Task Group, in Chicago IL. September 16, 1982 Ninth Meeting of the Task Group, in San Francisco CA.

- Failure of unsealed thermal spray. - Cracks in area that was shot peened. - Cracks found in an anodically protected soda digester - Cracking reported adjacent to corrosion resistant weld overlay. - Digester Cracking Research Committee (DCRC)

- Chairman: Dave Bennett - Vice-chairman: Sandy Sharp - Secretary: Dave Bowers

January 1983 Final report by to the DCRC by Ron Yeske of IPC on "Stress

Corrosion Cracking of Continuous Digesters for Kraft Pulping." March 4, 1983 Tenth Meeting of the Task Group, in Atlanta GA.

- Guzi reported on testing in the Grande Prairie digester. Non-stress relieved U-bends cracked; stress relieved U-bends did not crack. Unsealed plasma spray blistered. Cracks occurred adjacent to corrosion resistant weld overlay.

September 15, 1983 Eleventh Meeting of the Digester Cracking Subcommittee, in

Dallas TX. - Status changed from Task Group to Subcommittee. - Report of cracking of stainless steel nozzles. - Kamyr reported using Alloy 82 to overlay the circumferential weld seams in 20

digesters. - Anodic protection (AP) system installations looking good but some hardware

failures. August 1984 Final report to the DCRC by Sharad Pednekar of Battelle Columbus

on "Evaluation of Repair Methods for SCC in Continuous Digesters." August 1984 Final report to the DCRC by Doug Singbeil and Andy Garner of

Paprican on "Research Program to Investigate Cracking of Continuous Digesters."

September 19, 1984 Twelfth Meeting of the Digester Cracking Subcommittee, in

Boston MA. - Joint meeting with the DCRC. - More examples of cracking of stainless steel.

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Appendix B

March 29, 1985 Meeting of the Digester Cracking Subcommittee in Boston MA. - Grinding preparation of surfaces for nondestructive examination. - Overlay edge cracking. - In-situ corrosion monitoring

September 19, 1985 Meeting of the Digester Cracking Subcommittee in Atlanta GA.

- Draft of 5th Report reviewed: - Crack preventive measures (anodic protection, overlay, thermal spray

coating, shot peening) - DCRC summary:

- Only correlation of SCC was with lack of stress relief - SCC occurs only when corrosion potential in a critical range. - Cracking less-severe in lower-hydroxide liquors. - No cracking in simulated acid cleaning for 10 years.

- Inspection guidelines - Request for information (questionnaire).

March 18, 1996 Meeting of the Digester Cracking Task Group in Houston TX.

- First meeting with D. A. Wensley as chairman - Status reverted to a Task Group of the Pressure Vessel and Tank

Subcommittee - Reports on:

- Overlay edge cracking - Ultrasonic imaging

September 8, 1986 Report to the DCRC by Doug Singbeil and Andy Garner of

Paprican on "Stress Corrosion Cracking of Full-Thickness Digester Weldments."

September 23, 1986 Meeting of the Task Group in Seattle, WA.

- Report by Pat Morris of IP: - discontinued use of weld overlays due to edge cracking - using arc spray - first N.A. installation of an AP system with wall-mounted cathodes - ultrasonic imaging successful in locating cracks

March 9, 1987 - Meeting of the Task Group in San Francisco

- Cracking of carbon steel cooking nozzles (D.A. Wensley). - Disbonding of overlaid SS cladding in a batch digester (Ken Donaldson). - Serious preferential weld corrosion reported in a small continuous digester

(Chakrapani). September 16, 1987 - Meeting of the Task Group in New Orleans, LA

- David Crowe (IPC) secretary. - Forum on cracking of steaming vessels constructed using 304 stainless steel.

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Appendix B

March 24, 1988 - Meeting of the Continuous Digester Cracking Task Group in St. Louis - MEI Charlton report (D. Chakrapani)

- hot cracking of excessively-diluted nickel-base weld overlay - intergranular corrosion of stainless steel cladding adjacent to a

circumferential weld. September 22, 1988 - Meeting of the Task Group in Chicago, IL.

- Liquor heater tube corrosion and cracking forum. August 1989 Sixth report of the Continuous Digester Cracking Task Group,

"Cracking of Continuous Digesters: an Updated Survey," published in TAPPI Journal, Volume 72 No. 8, pp. 211-215 (1989).

- 73% of continuous digesters have experienced cracking. - SCC positively confirmed as the cracking mechanism in only 9 digesters. - Most cracking in digesters built between 1965 and 1971. - PWHT'd digesters are more resistant to cracking but severe cracking also

reported in 56% of PWHT'd digesters September 14, 1989 - Meeting of the Task Group in Atlanta, GA

- Overlay edge cracking - Anodic protection update

September 27, 1990 - Meeting of the Task Group in Seattle, WA

- Report by Max Moskal on through-wall cracking incident in Hodge, LA The cracks were adjacent to the central pipe support gussets.

- Report by Chuck Gaines on through-wall cracking in Valliant. OK. The digester was condemned.

October 3, 1991 Meeting of the Task Group in Nashville, TN.

- High pressure feeder forum. - Report by Neil Risebrough on the rapid thinning of a continuous digester in

Squamish, BC - Organizational meeting for the Continuous Digester Thinning Working Group

was held immediately after the Task Group meeting. April 28, 1992 First meeting of the Continuous Digester Thinning Working Group, in

Nashville, TN - Advisory bulletin and survey were sent out in November 1991. - Reports of rapid corrosion thinning of digester walls.

September 17, 1992 Joint meeting of the Continuous Digester Cracking Tank Group

and the Continuous Digester Thinning Working Group, in Boston, MA. - Report by Ian Munro on seminar on electrochemistry in kraft liquors. - Report by Pat Morris on applications of arc spray in batch and continuous

digesters.

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Appendix B

- Report by Max Moskal on local PWHT of two continuous digesters; SCC did not return in one digester but severe SCC recurred in the other.

March 8, 1993 Meeting of the Digester Thinning Working Group, in New Orleans, LA.

- Digester thinning survey update: - 31% of digesters reported rapid corrosion thinning

September 1993 Digester Thinning Survey Report presented as a paper during

the TAPPI Engineering Conference in Orlando, FL. Book 1, pp. 71-74. - Rapid corrosion thinning correlated with:

- high-temperature acid cleaning - operational changes to extended delignification, increased production, higher

temperatures. - pulping corrosive wood species

September 22, 1993 Meeting of the Digester Corrosion Task Group in Orlando, FL

- Presentation by Ian Munro on over-protection of stainless steel central pipes in digesters with AP.

March 18, 1994 Meeting of the Digester Thinning Task Group in Vancouver BC.

- A full-day meeting to discuss thinning of continuous digesters. - Results of a Kamyr AB survey of digesters outside North America were

presented. - digesters with MCC, EMCC, or ITC more prone to rapid thinning.

April 1994 Catastrophic failure of a weld overlaid batch digester in Panama City, FL. September 20, 1994 Joint meeting of the Continuous Digester Cracking Task Group

and the Continuous Digester Corrosion Task Group, in San Francisco CA. - Digester Protection Forum:

- Weld Overlay - Thermal spray coatings - Anodic protection

March 13, 1995 Digester Corrosion Information Meeting, in Vancouver BC.

- Name of task group changed to include corrosion and cracking problems in both batch and continuous digesters.

- Reports of cracking in carbon steel seam welds in a stainless steel weld overlaid batch digester.

- Report by Steve Clarke of Paprican on cracking of bottom scrapers. September 11, 1995 Digester Corrosion Information Meeting in Dallas, TX

- Presentation by Craig Reid on the long-term performance of stainless steel weld overlays in batch digesters.

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Appendix B

March 18, 1996 Digester Corrosion Information Meeting, in Vancouver BC. - Discussion on hydrogen cracking in continuous digesters.

September 17, 1996 Digester Corrosion Information Meeting, in Chicago, IL.

- Presentation by Bruce Lang on brittle cracking in batch digesters. March 3, 1997 Digester Corrosion Information Meeting, in Vancouver BC.

- Presentation by Garry Rustan on severe erosion-corrosion of the digester wall inside screen headers.

October 6, 1997 Digester Corrosion Information Meeting, in Nashville, TN.

- Forum on the use of duplex stainless steels for digesters. March 19, 1998 Digester Corrosion Information Meeting, in Vancouver BC.

- Forum on digester overlay using type 312 stainless steel. September 14, 1998 - Digester Corrosion Information Meeting, in Miami, FL.

- Forum on anodic protection of digesters. May 3-4, 1999 - Digester Corrosion Information Meeting, in Austin, TX.

- Forum on thermal spray coatings in digesters. September 13, 1999 - Digester Corrosion Information Meeting, in Anaheim, CA.

- Forum on cracking of solid stainless steel steaming vessels. February 24, 2000 - Digester Corrosion Information Meeting, in Providence RI.

- Forum on corrosion of carbon steels and stainless steels in kraft digesters.

September 18, 2000 - Digester Corrosion Information Meeting, in Atlanta, GA.

- Forum on corrosion of flash tanks. February 26, 2001 - Digester Corrosion Information Meeting, in Portland OR.

- Forum on rapid corrosion thinning of continuous digesters. June 13, 2002 - Digester Corrosion Information Meeting, in Toronto, ON.

- Forum on bottom scraper corrosion and cracking. - Forum on the use of duplex stainless steels for digesters and ancillary

equipment. September 11, 2002 - Digester Corrosion Information Meeting, in San Diego, CA.

Presentations by: - Hakan Dedorsson of AvestaPolarit on the rupture of a type 317L stainless steel

batch digester at a SAPPI mill in South Africa. - Brian Greenwood of Andritz on a corrosion accident in a continuous digester at

the PT Tel Musi mill in Indonesia.

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Appendix B

- Steve Pawel of ORNL on using electrochemical noise probes for corrosion monitoring in digesters.

- Angela Wensley of AWE Inc. on recent issues with digester corrosion and cracking.

- Winston Shim of Corrosion Service on anodic protection of the Pine Hill digester.

- Mike Place of Foster Wheeler on thermal spray coating of a circumferential band in a continuous digester.

March 6, 2003 - Digester Corrosion Information Meeting, in Atlanta, GA.

Presentations by: - Angela Wensley of AWE Inc. on external cracking of batch digester leg

supports. - Mike Macke of GE Inspection Services on re-cracking experience with carbon

steel weld restorations in continuous digesters. - Max Moskal of M&M Engineering on duplex stainless steel vs. carbon steel

construction for digesters and on issues with stainless-clad digesters. - Preet Singh of IPST on corrosion testing of thermal spray coatings for

digesters. - Martti Huttunen of Savcor on the anodic protection of two continuous digesters. - Bruce Newton of WSI on type 312 stainless steel weld overlay.- Angela Wensley of AWE Inc. on bottom scraper cracking and on duplex

stainless steel head cracking during manufacture. - Preet Singh on IPST research projects on corrosion in pulping liquors.

February 26, 2004 - Digester Corrosion Information Meeting, in Vancouver BC.

- Mark Gilkey (FM Global) secretary. Presentations by: - Angela Wensley of AWE Inc. on digester inspection. - Martti Huttunen of Savcor on anodic protection. - Andy Garner of Paprican on the DCRC research project. - Mark Bosma of Bowater on cracking and repair of the top head weld seam in a

continuous digester. - Dave Mauro of Canspec on surface preparation for inspection of continuous

digesters. - Chris Dault of Canspec on creation and use of a roll-out drawing for continuous

digester inspections. - Margaret Gorog of Weyerhaeuser on digester corrosion, protection, and

inspection. - Pani Chakrapani of MEI Charlton on 17 years of experience with a stainless-

clad digester in sulfite service. - Tim Charman of Celgar on weld overlay of a continuous digester. - Titak Linaksita of Conrex Steel on hot forming of duplex stainless steel heads

for digesters. - Craig Reid of Bacon Donaldson on examination of boat samples of type 312

stainless steel weld overlay from a batch digester.

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Appendix B

- Carl Plate of AEC Engineering on quality assurance for new duplex stainless steel digesters.

- Ralph Davison of Outokumpu on lean duplex stainless steel. March 21-22, 2005 - Digester Corrosion Information Meeting, in Glens Falls, NY.

First day presentations by: - Martti Huttunen of Savcor on three case histories of anodic protection of

continuous digesters. - Dave Bennett of Corrosion Probe on screen welding practice. - Gerry Ortner of Cariboo Pulp on weld overlay of a continuous digester. - Alex Nadezhdin of Nexfor on the effects of weld dilution on digester weld

overlay. - Angela Wensley of AWE Inc. on the Uddcomb method of weld overlay. - Heikki Leinonen of VTT Industrial (Finland) on the SCC susceptibility of duplex

stainless steel welds in kraft batch cooking. - Patrick Sullivan of Andritz on OEM experience with fabrication in type 2205

duplex stainless steel. - Ralph Davison of Technical Marketing Resources on duplex stainless steels for

digesters and related equipment. - John Grocki of Advantage Resources Consulting on duplex stainless steels for

kraft digesters. - Angela Wensley of AWE Inc. on experiences with fabrication and inspection of

duplex digesters. - Margaret Gorog of Weyerhaeuser on scraper arm cracking. Second day presentations by: - Angela Wensley of AWE Inc. on the revised TIP 0402-03 on digester weld

overlay. - Angela Wensley of AWE Inc. on the revised TIP 0402-27 on continuous

digester inspection. August 31, 2005 - Digester Corrosion Information Meeting, in Philadelphia PA.

- Final meeting of the Task Group, - Summary of Task Group activities over the past 25 years.

Submitted by: Angela Wensley Task Group Chairman 1986 2005 Note: minutes of the meetings since March 1994 are available in electronic form.

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TAPPI Digester Corrosion Task Group Meeting August 31, 2005 1

Agenda Item 4.1

Angela WensleyAngela Wensley Engineering Inc.

Overview of the TAPPI Digester Cracking / Corrosion Task Group

TAPPI Digester Corrosion Task Group Meeting August 31, 2005

Philadelphia, PA

Outline of the Overview1. In the Beginning2. Task Group3. Reports4. Aprs Bennett5. Corrosion Thinning6. Back to Batch7. For Your Information8. Digester Corrosion Information Forums9. Recent Issues10. Back to the Future

1. In the Beginning

September 26, 1980: Catastrophic failure of the continuous digester in Pine Hill AL. Failure occurred at a weld seam at a

circumferential-to-conical transition. Failure mechanism was caustic stress

corrosion cracking (SCC). SCC found in all welds in the non-post weld

heat treated top section of the digester. Top 6 rings and top head were replaced.

Failed Head

Appendix C


Grooves

CrackCrack

2. Task Group

October 29, 1980: Continuous Digester Cracking Task Group formed; Dave Bennett chairman.

Became the Continuous Digester Cracking Subcommittee (of C&ME) in 1983.

Often met jointly with the Digester Cracking Research Committee (DCRC).

3. Reports

The T.G./Subcommittee produced 5 reports between 1980 and 1985: Inspection findings Recommendations on proper inspection and

repair of cracks. Crack preventive measures (anodic

protection, thermal spray coating, weld overlay, shot peening).

Questionnaire on digester cracking.

4. Aprs Bennett

First meeting of the task group with Wensley as chair was in March 1996.

Sixth report on the results of the cracking survey was released in 1989. Cracks reported in 73% of continuous

digesters. PWHTd digesters most resistant.

5. Corrosion Thinning

1991: Report on rapid corrosion thinning of a digester in Squamish BC.

1991: Continuous Digester Thinning Working Group formed (Angela Wensley chair). Survey prepared by Dave Bennett.

1993: Report on results of thinning survey. Thinning related to change in operation to

extended delignification; higher temperatures; hot acid cleaning; corrosive wood species.

Appendix C


6. Back to Batch

1994: Catastrophic failure of a stainless steel weld overlaid batch digester in Panama City FL.

1995-6: reports on brittle cracking of carbon steel seam welds in batch digesters that had been overlaid.

7. For Your Information

1994: Name changed to the Digester Corrosion Information Meeting to reflect changes in scope: Both batch and continuous digesters. Cracking and corrosion. Ancillary equipment. Construction of new digesters and ancillary

equipment using duplex stainless steels.

8. Digester Corrosion Information Forums

1987: Cracking of SS steaming vessels 1988: Liquor heater tubes 1991: High pressure feeders 1994: Thinning of continuous digesters 1997: Duplex stainless steels 1998: Weld overlay using type 312 SS 1998: Anodic protection

8. Digester Corrosion Information Forums, continued

1999: Thermal spray coatings 1999: Cracking of SS steaming vessels 2000: Corrosion of CS and SS 2000: Corrosion of flash tanks 2001: Rapid corrosion thinning 2002: Bottom scraper corrosion/cracking

9. Recent Issues

Erosion-corrosion behind headers. Effect of wood species on corrosion. Corrosion and cracking of bottom scrapers

(duplex stainless steel cracks too). External cracking of leg supports for batch

digesters. Quality assurance during construction of

duplex stainless steel digesters.

10. Back to the Future

None of the current issues appears to merit maintaining a separate task group.

I recommend closing out the digester corrosion task group since its task has been accomplished.

Digester Corrosion and Cracking A Problem Solved?

Appendix C


Agenda Item 4.3

Charlie GuziRetired from Proctor & Gamble

Grande Prairie and Flint River Digester Cracking History

Charlie GuziSecretary for the Continuous Digester

Cracking Task Group 1980

Background

Joined TAPPI after attending the 3rdInternational Symposium on Corrosion in the Pulp and Paper Industry in 1980

Pine Hill digester exploded later in 1980 Invited to first meeting in Montgomery AL Volunteered to become secretary Traveled extensively with chairman Dave

Bennett over the next 2 years

P&G Mills

Grande Prairie (GP) Alberta Flint River (FR) Georgia

GP Fall 1980 Inspection

Cracks found in all welds inspected in the impregnation zone

Crack depth explored Most severe cracking (5/32 inch deep) in

downcomer support and lug welds Metallurgical sample removed. Cracking

confirmed as SCC Digester considered safe for operation

GP Spring 1981 Inspection

Extensive cracking found; maximum depth inch in circumferential and downcomer welds

Cracking removed from selected areas Crack preventive measures:

Shot peening Shot peening + Metco 444 plasma spray

Numerous U-bend specimens installed with various combinations of weld filler, overlays, plasma sprays, and stress relief

Appendix C


GP October 1981 Inspection

Severe cracking found in downcomer support welds; cracks ground out and weld repaired

Shot peened and plasma sprayed test areas appeared satisfactory

Due to extended outage for recovery boiler repairs, had time to grind out all cracks

Most weld areas shot peened + plasma sprayed (sealers no available)

GP July 1982 Inspection Shot peening and unsealed plasma spray had

failed after 14 months All welds were plasma spayed and then sealed

using a silicon-based sealer SCC of U-bend of A516-Grade 70 steel welded

using E7018 and to a lesser extent in U-bend welded using E6010

All other U-bends intact Acoustic emission testing done on digester was

inconclusive

GP December 1982 Inspection

Short (8-hour) inspection Sealed thermal spray confirmed to be

protecting the digester

GP Spring 1983 Inspection

Minor damage found to sealed plasma spray

Much of the damage was due to abrasive blasting to remove scale for visual examination

GP Fall 1983 Inspection

Most sealed plasma spray in excellent condition and appeared to be the most cost-effective solution to the digester cracking problem

Areas of coating failure were re-coated All plasma sprayed areas were re-sealed

using Metco CE2236 furan-based sealer

GP July 1984 Inspection

Sealed plasma spray in excellent condition No cracking found where the plasma spray

was removed for wet fluorescent magnetic particle testing

Repairs made using Metco 41C flame spray and a furan-based sealer

Appendix C


GP Top Replacement

The sealed plasma spray continued to protect the top of the digester until the top was replaced

An anodic protection system was installed

FR Fall 1980 Inspection

Prior to start-up the impregnation vessel (IV) and continuous digester were found to not be fully stress-relieved

The IV reached 950F for 5 hours A second 100% stress relief was

performed on the digester No additional stress relief was done on the

IV

FR Winter 1981 Inspection

Cracks found in many welds in the digester; all cracks at bottom edge of welds

Crack sample identified as hot cracking, an original fabrication flaw

No cracks found in the IV

Flint River Conclusion

A comprehensive inspection plan and defect removal plan was developed

Eventually all cracks were removed from the digester

When Charlie Guzi retired on March 31, 1991, no further SCC had been found in either the IV or the digester

Appendix C


Agenda Item 4.4

Sandy SharpMeadWestvaco

TAPPI/IPC Digester Cracking Research Committee

1980 - 1986

Digester Cracking Research Committee

What we knew in those days 1950s UT discovery of batch digester

thinning produced many theories Chemical theory - Stockman &

Ruus in Norway, Christiansen & Lathrop in Canada

CR = - a + b [NaOH] + c [Na2S] + d [Na2S][Na2SO3]

Effect of [Si] in steel 1960s Mueller used pstat to show

active-passive behavior basis for AP


Industry practice in those days Rates of thinning were slower in

continuous digesters, so less routine inspection

Difficult for inspector to see wall surface

Lalibert SCC comment inhibitive extractives?


September 1980 rupture of Pine Hill Digester TAPPI C&ME Task Group formed (CA4561) TAPPI Task Group sought to solicit industry

support for a research program to investigate digester cracking to identify effective control measures.

Funds solicited from mills with continuous digesters (85%) Kamyr, Inc. provided matching funds Several related firms provided additional funding IPC provided administrative support

TAPPI has never led research before or since

Appendix C



Representatives of sponsoring companies formed (DCRC) -- to steer the research.

DCRC Research Subcommittee solicited research proposals and chose 4:1. Crash program to review current understanding

of SCC in alkaline sulfides (IPC), effects of fabrication and operation, chemical and electrochemical characterization of liquors. Study 3 crackers, 3 non-crackers. Report by end of 1982.

Large non stress-relieved vessels more susceptible.

Steels and welds drift into passive zone.


2. Liquor conditions in continuous digesters (IPC)

[NaOH] as process proceeds C and NC liquors could support SCC3. Coatings and weld overlays for preventing

SCC (Battelle Columbus) Delays and disappointing results4. Evaluation of SCC prevention strategies in

full size welds (PAPRICAN) Stress relief, peening, tspray, temper-bead,

6010 cap all reduce SCC susceptibility

Digester Cracking Research Committee some observations

Very broad effort to address industry problem Major funding from individual mills and

suppliers, but not from government Extraordinary confluence of circumstances

Mills understood size of problem TAPPI enabled cooperative funding solicitation Manufacturers cooperated openly M-B, UBC and Hammermill had researched

electrochemical foundations Structure paved way for DOE-funded 2020 and

OIT projects

Digester Cracking Research Committee some stars!

TAPPI Dave Bowers Ron Yeske Carl Elmore Bob Charlton Angela Wensley

Des Tromans Doug Singbeil Dave Crowe Andy Garner Dave Bennett

Appendix C


Agenda Item 4.4

Doug SingbeilPaprican

SCC IN DIGESTERS AND ELECTROCHEMICAL

POTENTIAL

Doug SingbeilPaprican

Tappi Digester Cracking Program(1982-1985)

How Does Liquor Chemistry Affect Cracking?

Severity decreases with decreased NaOH

Independent of Na2S203, Na2SO3, NaCl, Na2CO3

Some organics/species inhibitive Potential range for cracking mostly

independent of NaOH level

Slow strain rate tensile tests showed how cracking depended on electrochemical potential

Fracture mechanics specimens were used to determine the rate of crack propagation

Appendix C


Under ideal conditions, cracks grow at ~ 10 mm/y, but not when anodically protected

In situ fracture mechanics specimens demonstrated the value of anodic protection

Electrically bonded to digester(anodically protected)

Electrically isolated from digester(unprotected)

Overload

SCC

Overload

Precrack

Precrack

Appendix C


Agenda Item 4.6.1

Ian Munro

Development of Anodic Protection to Prevent Cracking

Ian Munro P.Eng.N.A.C.E Corrosion and Cathodic Protection

Specialist

Sorry I could not attend the meeting! See you next year! Timing In Life is Everything!

Research Singbeil and Tromans

PAPRICAN

ExperienceWalter MuellerTom Watson

Risk Taker Dave Bennett

Need

Pine Hill

Development of Successful Commercial Technology

Anodic Protection of Digesters

Experience

Batch Digesters - Mueller, Watson and Webster Late 1950s and 1960s Successfully Protected Several Kraft Batch

Digesters Protected a Stainless Steel Overlaid Digester

Systems Did Not Reach Commercial Success

How I Got Involved With Anodic Protection

Tom Watson Had An Inquiry To Protect a Cast Iron Vessel Containing 96% Boiling (315 C) Sulphuric Acid

Tom Was Brilliant but a Little Handless He Continually Spilled the Acid over his Clothes

and Shoes Harry Webster Was Convinced That Tom Would

Kill Himself !!! Harry Insisted that I Do the Work to Save his

Friend

Appendix C


Risk Taker - 1978

Bennett Found a Serious Corrosion Problem in a Soda Continuous Digester Corrosion Rate - 200 mpy Corrosion in Upper Area of Digester

Bennett Contacted Watson Due to His Previous Experience in Batch Digesters

As I had Saved Tom Watsons Life from a Certain Sulphuric Acid Death, Anodic Protection became One of My Specialties

Risk Taker 1978 (Continued)

Anodic Protection Was Installed with the Objective of Reducing Corrosion Rate to Buy Time to Repair the Vessel

Anodic Protection Reduced the Corrosion Rate to Zero and Operated for Over 20 Years

First System Design

Pipe Type Cathode around Centre Pipe Magnesium and Stainless Steel Reference

Electrodes 200 Amp Potential Controlled Rectifier Rectifier was Located on the Top of the

Digester in the Dog House

The First Research

Singbeil, D. and Tromans, D. Stress Corrosion Cracking of Mild Steel in Alkaline Sulphide Solutions 3rdInternational Atlanta Spring 1980 Confirmed that Cracking was Potential

Dependent A Number of Us thought that it was Great

Work but we knew that Digesters dont Crack

The Main Event

On Sept 26 1980 the Pinehill Digester Experienced a Sudden Separation of the Top Section Investigation Indicated that the Cause of the

Failure was Caustic Cracking So Much for Our Opinion that Continuous

Digesters Do Not Crack

T.A.P.P.I. Digester Cracking Research Program

Research by PAPRICAN Reconfirmed that Cracking was Potential Dependent As Such, Anodic Protection would Completely

Eliminate the Problem

Appendix C


The First Kraft Digester Design was Similar to Soda Digester (All Carbon

Steel Components) The Mill Used the Logic If Carbon Steel is

Good then Stainless Steel is Better for the Conductor to the Cathode

This Material Change Resulted in an Excellent Example of Hydrogen Cracking of Stainless Steel

The Mistake was Corrected and the System is Still Operating

The 2nd Kraft Digester Anodic Protection System

Summary

Anodic Protection of Continuous Digesters Only became a Viable Method to Prevent Cracking as a Result of the Coming Together of: Prior Experience Research A Risk Taker A Need

Appendix C


Agenda Item 4.6.2

Winston ShimCorrosion Service Company

Anodic Protection of Digesters

Winston Shim, P. Eng.Corrosion Service Co. Ltd.

Markham, OntarioCanadaL3R 5J8

Pioneer Work on Anodic Protection of Digesters

Research on Anodic Protection of batch digesters originated by Walter Mueller of PAPRICAN (1950s)

First successful batch digester installation by Thomas Watson of Corrosion Service in 1957

Batch Digester Anodic Protection

Proved Anodic Protection can stop corrosion in batch digester environment

Technological success but hardware made the implementation difficult (ie, current sources not suitable for AP)

AP of Continuous Digesters

First installation of continuous digesters was on a soda digester in 1979

Corrosion was successfully mitigated

AP of Continuous Digester

Catastrophic digester failure occurred in 1981due to stress corrosion cracking (SCC)

Anodic Protection system was installed in 1985 to prevent SCC

Original design was split pipe cathode longitudinally and install on center pipe at the impregnation zone

Appendix C


Design History

Pipe-on-pipe cathode at impregnation zone of conventional cooked digesters

Top Separator and lower zone protection systems were added

Linear Distributed Cathode (LDC) design for even current distribution (early 1990s)

Newer cooking schemes (ie, Lo-Solids, EMCC, etc.) resulted in new challenges at the lower zones of digesters

Acid Cleaning of Digesters

Coupon steadies showed acid may not mix while being injected into the digesters causing quite severe corrosion

Early Remote Monitoring System

Appendix C


Appendix C


Agenda Item 4.6.3

Martti HuttunenSavcor Inc.

TAPPIDigester corrosion information meeting

Developments of AP SystemMartti Huttunen

Philadelphia, PAAugust 31, 2005

Anodic Protection Concept Process System

1. Control unit2. Rectifiers 3. Cathodes4. References5. Monitoring

Feed back1. CER2. Results

AP System Schematic

Control unit

1. Analog control unit 1980s

2. Digital control unit 1985s

3. PC based control unit 1995s

4. Modular control unit 2006

Rectifiers

AC / DC 380 V 0-15 V 250 Amps

Appendix C


Cathodes

1. Crown cathode 2. Flat vertical or horizontal cathodes 3. Dummy plate cathodes 4. Rod cathodes 5. Taylor made cathodes for heaters etc.

Old & New Design

Dummy Plate & Rod Cathodes References

Molybdenum based mV reading Temperature reading Polarization scans

Monitoring

On-line monitoring Start up/ Shut down Alarms Monthly reports

150

170

190

210

230

250

270

290

310

330

350

1-Jun-04 2-Jul-04 2-Aug-04 2-Sep-04 3-Oct-04 3-Nov-04

Tem

pera

ture

in F

ahre

nhei

t

D133T D167T D299T D308T

Digester Anodic Protection

0 12 24 36 48 60-1010

-810

-610

-410

-210

010

-70

-16

38

92

146

200

T im e , m in

Res

ista

nce,

kO

hm Current, m

A

R e s is ta n c e & C u r re n t v s T im e

Studies - CER

Appendix C


AP Operation04.03.2003 Savcor Consulting Inc15:50:47 230-1130 West Pender Street

Anodic Protection System Vancouver, B.C. V6E 4A4 CanadaContinuous digester On _---_ Tel. +1-604-6627034

On Liquor |___|/ \ Ref Temperatures

On Impregnation _____ 308-R1 47 mV 211 F

On Cook blank 299-R1 88 mV 236 F_____ 287-R1 115 mV 251-R1 78 mV 228 F

On Cook 238-R1 153 mV_____ 217-R1 142 mV

On Extraction 198-R1 36 mV 214 F_____ 179-R1 204 mV

On Wash upper 167-R1 210 mV 231 F----- 155-R1 213 mV

On Wash middle 133-R1 197 mV 258 F----- 115-R1 81 mV

On Wash lower -----

On Bottom |_____|

Inspection Report and Outage Support SummaryMay 2002

Continuous DigesterSouthern Mill

Executive Summary

No new cracks were found in areas of the impregnation zone that were previously cleared of cracks. Additionally, no obvious propagation of existing cracks was noted. This is far more consistent with the expected effects of anodic protection.

Corrosion rates in the lower zones of the digester continue to be essentially too low to measure.

Southern Mill

Kamyr Digester

Comparison of Previous and Present Thickness Readingstaken in wash area

to monitor Anodic Protection System Performance(Loss/Gain is in Inches)

October 2000GAIN / LOSS

RING 1A RING 4H1 H2 H3 H4 Average H1 H2 H3 H4 Average

V1 0.004 0.002 0.005 0.003 0.0035 V1 0.006 0.004 0.002 0.005 0.00425V2 0.005 0.004 0.005 0.003 0.00425 V2 0.011 0.004 0.004 0 0.00475V3 0.007 0.004 0.006 0.004 0.00525 V3 0.004 0.005 0 0.002 0.00275V4 0.008 0.004 0.006 0.003 0.00525 V4 -0.002 0 0.004 0.002 0.001

Average 0.006 0.0035 0.0055 0.00325 0.004562 Average 0.00475 0.00325 0.0025 0.00225 0.003187

RING 1B RING 8H1 H2 H3 H4 Average H1 H2 H3 H4 Average

V1 0.008 0.003 0.007 0.004 0.0055 V1 0 0.003 0.002 0.003 0.002V2 0.008 0.002 0.003 0.004 0.00425 V2 0 0.001 0.003 0 0.001V3 0.004 0.001 0.006 -0.002 0.00225 V3 0.002 0 0.005 0.001 0.002V4 0 0.002 0.005 0.003 0.0025 V4 0.002 0.002 0.001 0.002 0.00175

Average 0.005 0.002 0.00525 0.00225 0.003625 Average 0.001 0.0015 0.00275 0.0015 0.001687

Remaining Years to ASME Min.

2005 2003-2005 Minimum ASME

MinimumRemaining Thickness

Average

Ring Thickness (inches) (inches) Loss(inches) (inches)

14 1.832 1.185 0.647 ~0 Indefinite7 1.823 1.351 0.472 0.008 >100 years5 1.653 1.387 0.266 ~0 Indefinite3 1.528 1.422 0.106 0.003 70 years

Remaining Years to ASME Minimum Wall in No. 1 Digester

Using the Minimum UT Values Measured in Each Ring.Years to Go

Before ASME

Minimum

THANK YOU FOR YOUR TIME !

Thank you Angela

Savcor Consulting Inc.

Appendix C


Agenda Item 4.7.1

Max MoskalM&M Engineering

Panama City Digester FailureApril 1994

Appendix C


Agenda Item 4.7.2

DSS Digesters in North America

Max MoskalM&M Engineering

Purpose of Survey:

Determine number of in-service digesters, both batch and continuous

Assess experiences to date Estimate future DSS use for digesters

Batch Digesters

27 In-service completed 5 Re-build completed ? In planning stage

Continuous Digesters

1 Top replacement completed 1 Impregnation vessel completed 1 Single vessel digester completed

Appendix C


Thickness Survey ResultsKraft Batch Digesters

1 digester with 20 to 25 mpy shell loss 1 digester with erosion-corrosion at outlet 4 digesters reported no loss after 5 years

October

2002

February

2004

DSS Cost Comparison

2304 Cost = 1.00

2205 Cost = 1.75

Nozzle Deflectors

Summary

DSS adopted by 14 different paper companies for batch & continuous digesters since 1997

Both kraft & sulfite applications Most experience with 2205 DSS Some in-service corrosion reported 2403 has cost advantage over 2205

Appendix C


Agenda Item 4.8

Craig ReidAcuren

BATCH DIGESTER CORROSION

A WEST COAST MILL1953 - 2005

Conventional operation with external liquor heaters

High NaCl liquor due to ocean transport of logs

White liquor and chips added from the top

2 additional bare batch digestersKamyr digester

1962

Hot plate boiling recognized as cause of corrosion Paper Published in Pulp and Paper Magazine of Canada, vol. 59, no.1 , 1958. Hans Wegerif

1957

2.8 mm (0.11) spot welded30 mm (1 3/16) shell51 mm (2) shell

2 Inconel 600 lined

6 bare A285C

1953

2.8 mm (0.11) spot welded24 mm (15/16) thick shell

4 316L lined1950

Appendix C


CORROSION RATES

0.07 mm/year0.003 /yearInconel 600 lining

1997 Measurements

1957 Measurements

but 316L linings had serious local thinning within 2 years of start up and required ongoing repair

0.24 mm/year0.009 /year1960s SAW22% Cr

0.05 - 0.06 mm/year0.002 0.003/yearInconel 600 lining

0.23 mm/year0.009/year316L lining2.4 mm/year0.095/yearunlined

2205 and Inconel 600 sheet and strip lining installed in barrels over old overlay and Inconel 600 lining, and in dome over bare carbon steel and hot cracked 310 overlay

1995 - 1999

Re-overlay program in barrels due to thinning of SAW overlay - costly

1993 - 1995

Manual overlay in domes and cones 310 filler hot cracked

1980 1995

SAW overlay of barrels of bare and 316L lined digesters - 20 22% Cr deposits

1965 - 1980

316L liners maintained by Inconel 600 strip lining and local weld overlay

1960 - 1965

Weld overlay program resumed:312 filler applied over old overlay by SAWUp to 30% Cr obtainedBut cracking through full thickness of new overlay

2002

Lining program terminated due to: Severe general corrosion of bare carbon

steel under leaking lining in barrels SCC of old overlay and bare carbon steel under leaking lining in domes

A dome leaked due to SCC under a leaking lining. Two domes replaced with thicker carbon steel

2001

Useful service life of Inconel 600 lining = 44 years

Original Inconel 600 lining removed and replaced with P-GMAW 312 25 to 26% Cr over bare carbon steel - no

cracking, fissuring or porosity

2005

Re-overlay program continued using GMAW, FCAW, P-GMAW over old overlay30% Cr obtained without cracking but minor subsurface fissuring with GMAW, P-GMAW

2002 to date

Appendix C


Appendix C


LINING Starting in 1995 slot welded wallpaper sheet lining was

installed over old overlay. 2205 and Inconel 600 liners were used. Aim was to protect overlay against hot plate boiling.

The liner plates leaked but the overlay beneath was not attacked. Lining evolved to 6 wide strip lining seal welded to the shell instead of wallpapered.

Lining was applied in several digesters until it became apparent that severe corrosion, including SCC, was occuring under leaking liners

Appendix C


312 Re-overlay over old SAW #12 SAW re-overlay in 2004 not successful due

to severe cracking of overlay

high Cr obtained but high ferrite, and hardness led to cracking through full thickness of the new overlay

Appendix C


Hardness Versus Chromium for SAW Reoverlayin #12 Batch

220

240

260

280

300

320

340

23 24 25 26 27 28 29 30 31 32 33

Chromium (%)

Mic

roha

rdne

ss (V

HN

)

30-15#4

30-15#2

28-11#7

28-10#5

32-15#3

32-15#8

32-15#7

WSI 312

Inco-Weld 31230-15 GMAW

#7 Batch

cracking In 2003 FCAW 312 overlay was performed in the #7 Batch digester

25 28% Cr was obtained over previous SAW overlay

The FCAW overlay was sound

FCAW

Appendix C


312 pulsed MIG over existing 1991 overlay in

top 13 feet of the barrel

Exocor 312 filler 1991 overlay was in good

condition

West Coast Industrial

2004

Removed 1965 overlay by gouging

309 SAW applied Alloy Cladding

1991

309 SAWAlloy Cladding

1965

P-GMAW #3 Batch

Appendix C


CHART 2 HARDNESS VS % CHROMIUM

220

240

260

280

300

320

340

23 24 25 26 27 28 29 30 31 32 33

Chromium (%)

Mic

roha

rdne

ss (V

HN

)

30-15 #4

30-15#2

28-11#7

28-10#5

32-15#3

32-15#8

32-15#7

WSI 312

Inco-Weld 31230-15 GMAW

#7 Batch

cracking

Exocor 312 GMAW-P#14 2005 #3 2004 #9 2005

Base series (blue diamonds) is SAW Overlay in #12

Exocor 312 #11 2005

Incoweld 312 #11 2005

Appendix C


Agenda Item 4.9

Margaret GorogWeyerhaeuser

Digester Scraper Arm Cracking2205, 304L/Carbon Steel

Margaret GorogAugust 2005

Experience with 2205 scraper arms

ID Type HistoryA solid As of fall 2004, no indications in 7 yearsB box Widespread cracking was detected after 16 months. It was returned to

service without repair and replaced 18 months later. After 1 year, the stress relieved, reinforced carbon steel arms show minor wear.

C solid Clear after the first 12 months. 15 months later small cracks were seen in the attachment welds of the inner paddles. There are no plans to replace the arms.

D box Clear after the first 7 months. 12 months later small cracks were detected in the fillet weld that attaches the outer, end paddle to the arm. There is a crack in the paddle. After another 12 months the indications have not changed. There are no plans to change out the arms. They have outperformed carbon steel with 304L cladding.

E solid No indications after 32 months (3 inspections)F solid Extensive cracking after 15 months. It was returned to service without

repair and was replaced 12 months later with carbon steel arms overlaid with inconel. The entire unit was stress relieved.

G solid No indications after 21 months (2 inspections) First inspection of 2205 duplex stainless steel arms after 16 months (B)

A closer view of the end paddle (B) The same view after the arms were removed from the digester (B)

Appendix C


View of the bottom side post removal (B) View of the other arm from the bottom (B)

Cracking after 15 months of operation (F) A different view from the bottom (F)

Attachment weld indications (C) One, straight plate crack was cut out as a boat sample (C)

Appendix C


The crack is transgranularconsisting of one primary branch and fine secondary branches.

This was identified as environmentally assisted cracking.

There were no deficiencies of the 2205 stainless steel.

Boat Sample Analysis (C)

Results of the 2004 inspection no change in 2005 (D)

No maintenance in 7 years (A) A close-up of the machined surface shows little wear (A)

Observations

There is no correlation between cracking and the age of vessel, cooking process, arm style (solid or box).

Corrosion has not been an issue on the adjacent shell and head. Typically the material is carbon steel.

The cracks have the appearance of fatigue especially in carbon steel. Is mechanical loading understood? What role does it play in the cause of rake arm cracking?

More Observations

304L liners and 309L overlay have been the least successful in terms of maintenance.

Carbon steel, 304L and 2205 have all cracked. Experience with 2205 suggests that cracking does

not occur on a continuous basis. In the majority of cases 2205 is an improvement

over other stainless steels. There is still the risk that it will crack.

Recent material selection has focused on stress relieved, carbon steel with reinforcement or Inconel overlay on the leading edge. Wear is still an issue.

Appendix C


Agenda Item 4.10

Andy GarnerAndy Garner and Associates Inc.

TAPPI Digester Corrosion Information Meeting

(1980-2005)What have we learnt?

Cracking Happens Why do carbon steel digesters crack?

Stress Corrosion Cracking NaOH & stress & temperature &

active/passive potential

Why do carbon steel digesters crack?

Stress Corrosion Cracking NaOH & stress & temperature &

active/passive potential Welding Related Cracking

Cold cracking from hydrogen during welding Can be mistaken for stress corrosion

How Does Liquor Chemistry Affect Stress Corrosion Cracking?

Severity decreases with NaOH level Independent of Na2S203, Na2SO3, NaCl,

Na2CO3 Some organics/species inhibitive Potential range for cracking independent

of NaOH level

Appendix C


Does Microstructure Affect Stress Corrosion Cracking?

Cracks in HAZ and intergranular Weld metal has more secondary cracks Crack velocity depends on stress-intensity Stress corrosion crack growth rates do not

exceed ~ 0.5 in/year in digester liquors

Does Acid Cleaning Cause Stress Corrosion Cracking?

Lab tests could not demonstrate that acid cleaning caused cracking

Why Do Some Digesters Remain Uncracked?

Low residual stress Organic inhibitors Wrong potential

Which Vessels are Susceptible to Stress Corrosion Cracking?

Carbon steel vessels Continuous digesters Batch digesters Flash tanks Level tanks Liquor tanks

How Can Cracking Be Prevented?

Stress relief anneal - successful Anodic protection - successful Sealed plasma - successful


Stress relief anneal - successful Anodic protection - successful Sealed plasma - successful SS weld overlay partially successful Shot peening partially successful

Appendix C



Stress relief anneal - successful Anodic protection - successful Sealed plasma - successful SS weld overlay partially successful Shot peening partially successful Carbon steel weld - not successful Grinding/gouging not successful

Carbon Steel Digesters- general corrosion

Continuous digesters lower digester corrosion

liquor chemistry effect low caustic levels higher temperatures

flow-related corrosion Batch digesters

splash zone corrosion ss weld overlay commonly applied

Other issues with Continuous Digesters

Cracking of bottom scrapers related to high operating & residual stresses,

liquor chemistry stress relieved Alloy 600 overlay appears

immune; duplex ss not so

Stainless Steel and Kraft Liquors

Corrosion rate depends on Cr content Continuous digesters

304L cladding can be sensitized full stress relief not possible

Batch digesters ss weld overlay widely used, dilution control an issue,

All vessels solid duplex sss now used, few problems to date

Cracking doesnt need to happen

Appendix C

Documents

Tappi 2005 Digester Corrosion Information Meeting