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Duplex Stainless Steels

Margaret Gorog Federal Way, WA

Pulp and Paper Corrosion Symposium Georgia Tech Renewable Bioproducts Institute

November 2014

2205 stainless steel

Microstructure: austenite + ferrite

304L stainless steel

Microstructure: austenite

Duplex Stainless Steel

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• First 2 digits: nominal chromium • Last 2 digits: nominal nickel

2205 → 22% Chromium, 5% Nickel

• Family of Grades

• Lean • Standard • Super • Hyper

• 329 one of the oldest grades • 3RE60, Alloy 86 for suction rolls

Duplex Stainless Steel

• Improved corrosion and more importantly, stress corrosion cracking resistance

• Higher strength and hardness. This provides improved fatigue and wear resistance

• Higher tensile and yield strength compared to the austenitics translates into thinner walls and less weight which can offset the cost to some extent.

Duplex Stainless Steel - Benefits

Austenitic Tensile Yield

304/304L 75 30

316/316L 75 30

317L 75 30

6% Mo SS 95 45

Duplex Tensile Yield

Lean DSS 94 65

2304 87 58

ATI 2003 95 65

LDX2404 99 70

2205 95 65

2507 116 80

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• Limitations • More difficult to weld, especially the grades

containing molybdenum • Temperature limit of 600 °F • Availability particularly non plate forms • Cost not always advantageous even though alloying

cost is less Lean DSS 304L 2205 316L 317L 2507 6% Mo

Duplex Stainless Steel - Limitations

plate cost

Duplex Stainless Steel – Welding

• Welding is seen as a disadvantage but is probably no more difficult to weld than the austenitics – Make sure material starts out in the right condition

through composition and heat treatment – Use ASTM A923 Standard and ASTM A1084 Lean for

detecting detrimental intermetallic phases in DSS

• Maintain ferrite-austenite phase balance – Apply a low range of heat input

• Use appropriate weld filler – 2209 with additional nickel for 2205

• There is a limit as to how many times a duplex can be welded (lean DSS more forgiving)

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Duplex Stainless Steel - Embrittlement

UR2202 ATI2102

NSSC2120 LDX2101

2304

Similar to 304L Similar to 304L Similar to 304L Equivalent to 304L, not always equivalent to 316L Equivalent to 304L and 316L

Lean DSS – Corrosion Resistance

Lean duplexes contains little or no molybdenum Lower corrosion resistance than 2205 Ideal for alkaline liquor service

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Coupon Testing Results

Alloy Corrosion Rate (mpy)

304L 0.001

316L 0.004

Alloy 20 0.002

600 0.000

2101 0.003

2304 0.001

2003 0.003

2205 0.001

White Liquor Surge Tank

Alloy Corrosion Rate (mpy)

304L 0.001

316L 0.017

Alloy 20 0.002

600 0.029

2101 0.003

2304 0.000

2003 0.000

2205 0.000

3rd Effect Evap 45% BL Solids

Green Liquor Clarifier

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ATI2003

LDX2404

2205

Contains Mo More resistant than 304L or 316L. Substitute for 317L Does not have the corrosion resistance of 2205

Is the standard DSS grade and can be considered a commodity item. It comes in most forms.

Contains Mo Superior to 316L and 304L More resistant than 317L, resistant to low residual

chlorine dioxide solutions

Duplex Stainless Steel – Corrosion Resistance

Pre – Bleach Tank

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Ferralium 255 2507

Zeron 100

2707, 3207

Contains Mo, more difficult to weld, substituted for 6% mo SS in bleach plant Hyper DSS, Offshore oil applications

Super, Hyper – Corrosion Resistance

• The thermal expansion coefficient is close to carbon steel. With increased strength, they are less likely to crack than austenitic stainless steel linings.

• NACE SP0292 provides a specification for installing corrosion resistant sheet linings

• Less welding for larger sheets (10’ x 5’)

• Quicker to install vs overlay in a digester

• Less maintenance than tile lined towers

Duplex Stainless Steel Linings

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Nominal Alloying Alloy

UNS

number %Cr %Ni %Mo

Other

Elements PREN

304L S30403 18 8 N 18

316L S31603 16 10 2 N 24

317L S31703 18 11 3 N 30

254SMO S31254 20 18 6.1 Cu, N 43

AL-6XN N08367 20.5 24 6.3 Cu, N 45

19D S32001 20 1.7 0.3 N, 5Mn, Cu 23

UR2202 S32202 23 2.5 0.3 N 26

ATI2102 S82011 21 1.5 0.3 N, Mn 26

NSSC2120 S82122 21 1.5 0.3 N, Mn, Cu 26

LDX2101 S32101 21.5 1.5 0.3 N,5Mn, Cu 26

2304 S32304 23 4.5 0.3 N, Cu 26

ATI 2003 S32003 21 3.5 1.6 N 30

LDX2404 S82441 24 3.5 1.6 N, Mn, Cu 33

2205 S32205 22 5 3 N 35

Ferralium 255 S32550 25.5 5.5 3.5 N,2Cu,W 38

2507 S32750 25 6.5 3.5 N,Cu,W 41

Zeron 100 S32760 25 7 3.5 N, Cu, W 41

Cast Duplex Stainless Steels

UNS Number

Common Name

ASTM A890

Type

Wrought Equivalent

J93370 CD4MCu 1A 25Cr-5Ni-Mo-Cu

J93372 CD4MCuN 1B 25Cr-5Ni-Mo-Cu-N

J93373 CD3MCuN 1C 25Cr-6Ni-Mo-Cu-N 255

J93345 CE8MN 2A 24Cr-9Ni-Mo-N

J93371 CD6MN 3A 25Cr-5Ni-Mo-N

J92205 CD3MN 4A 22Cr-5Ni-Mo-N 2205

J93404 CE3MN 5A 25Cr-7Ni-Mo-N 2507

J93380 CD3MWCuN 6A 25Cr-7Ni-Mo-N Zeron 100

J93379 7A 27Cr-7Ni-Mo-Cu-N

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Bleach Plant Material Selection • O2 Delignification

– Historically 316L

– Switched to 2205 for external stress corrosion cracking resistance

– Now lean DSS

• E stage – Alkaline Conditions, less aggressive

– 316L/317L

– Lean DSS may be suitable

– Avoid titanium with peroxide

Bleach Plant Material Selection • D stage

– Resistance to oxidizing chlorides is necessary to prevent pitting and crevice corrosion

– Titanium up to the point of injection – Nickel alloys corrode in neutral (pH>3) ClO2

– Historically 317L, 6% molybdenum stainless steels depending on chlorine dioxide residual

– “Super Duper” 7% moly stainless steel, 654SMO, for more corrosion resistance

– 2205 or 2507 and cast equivalents now have wide applicability

– Substitute duplex solid plate or sheet lining for tile lined towers, chests or washers

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D2 Filtrate Corrosion

Temperature: 160-200 °F pH: 3.3-4.0 ClO2 concentration: 0.08 g/l Test duration: ~345 days in the D2 filtrate tank Materials: 317L, 2205, 254SMO, Titanium

Corrosion Results

Aloy Corr Rate (mpy) Crevice Pitting Open Pitting

Titanium Gr. 2 0

254SMO (6% Mo) 0.26 X

2205 0.20 X X

317L 1.95 X X

317L 2205

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D1/D2 Filtrate Immersion Testing

Temperature: 140 °F pH: 2 - 3 ClO2 concentration: low Test duration: 1 year

Temperature: 160 °F pH: 5 - 6 ClO2 concentration: low Test duration: 1 year

Corrosion Rates Alloys for Corr Rate D2-1 (mpy) 316L 0.001 317L 0.002 2205 0.000 CD4MCu 0.001 254SMO 0.000 AL6XN 0.003 625 0.056 C276 0.044

Alloys for Corr Rate D1-1 (mpy) 316L 0.000 317L 0.001 2205 0.001 CD4MCu 0.001 254SMO 0.000 AL6XN 0.001 625 0.001 C276 0.010

Alloys for Corr Rate Pitting, % D2-2 (mpy) Crevice area 316L 0.022 55 317L 0.002 10 2101 0.008 6 2003 0.000 2304 0.000 2205 0.000 AL6XN 0.004 C276 0.075

Alloys for Corr Rate D1-2 (mpy) 316L 0.001 317L 0.000 2101 0.000 2003 0.000 2304 0.000 2205 0.000 AL6XN 0.000 C276 0.007

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D2 316L results

LDX2101 317L

D2 317L, LDX2101

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Vapor Space Corrosion

D1 Two Years No Pitting

Coupon ID Corrosion Rate (mpy)

Description

LDX2101 0.054 Pitted

316L 0.035 Pitted

2304 0.033 Pitted

317L 0.012 Pitted

ATI2003 0 Clean

2205 0 Clean

AL6XN 0 Clean

Coupon ID Corrosion Rate (mpy)

LDX2101 0.001

316L 0.001

2304 0.001

317L 0.001

ATI2003 0.000

2205 0.001

AL6XN 0.001

D2 Five Years Pitting in crevice and open areas

Bleach Plant Materials Summary

• The bleach plant is not as corrosive as it once was

– Improved operations has led to lower chlorine dioxide residuals

– 2205 can be substituted for 317L

– Know residual, pH, temperature and test materials

– Lower alloys than those used in the past may be suitable

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Machine Room

• Duplex suction roll shells, excellent corrosion fatigue resistance

• Duplexes are not widely used for whitewater service since 304L and 316L are usually resistant.

• Lean grades are not available as piping

• 2205 is used for starch tanks and piping because of it’s resistance to stress corrosion cracking in hot, high chloride solutions.

Starch Piping – What Happened?

2205, installed as a replacement for cracked 316L, corroded and leaked after 2 years.

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Second phase precipitation in the pipe segment indicates reduced corrosion resistance. It did not occur in the elbow.

Elbow Pipe

• The pipe, unlike the elbow, had been delivered with an inadequate solution anneal and quench

• The annealing temperature is about 1900 °F. Precipitation occurs in 2205 when the metal is slow cooled through 1600°F for some time.

• If the material is water quenched from the solution annealing temperature, then there is enough time available for additional thermal cycles such as hot forming or welding before second phases begin to form.

• Due to poor heat treatment, second phase precipitation occurred in the pipe during the welding thermal cycle.

• In this case welding quality was not an issue

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Starch Tank

photo courtesy Gina Aiello

Duplex Stainless Steel Summary

• Benefits compared to common stainless steels:

Improved corrosion and stress corrosion cracking resistance

More resistant to external cracking under insulation

Higher strength. This provides improved fatigue and wear resistance

• Welding must maintain the duplex structure, especially the grades containing molybdenum

• Availability

• More Information - Practical Guidelines for the Fabrication of Duplex Stainless Steel – published by IMOA

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Questions