Challenges Meeting Temper Embrittlement Criteria with Welding Consumables

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Challenges Meeting Temper Embrittlement Criteria
with Welding Consumables
IPEIA 2007 14-17 February 2007

• William F. Newell, Jr., PE, IWE

EUROWELD, Ltd.
2
Advanced Materials

• When asked about his position on the reliability
  of advanced materials P91, 92, CrMoV, etc.), Dr.
  Martin Prager (Exec Dir. WRC) related how he
  answered a similar question when he was asked to
  speak at an international conference on the same
  topic Advanced materials will be less reliable
  because we will push them harder.
• -ASME II TG Creep Strength-Enhanced Ferritic
  Materials 25 Feb 2004

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API 934 1st Edition, 2000
Materials and Fabrication Requirements for
2-1/4Cr-1Mo 3Cr-1Mo Steel Heavy Wall Pressure
Vessels for High Temperature, High Pressure
Hydrogen Service
4
API 934s

• 934-A, Second Edition (pending revision)
• Materials and Fabrication Requirements for 2
  1/4Cr-1Mo,
• 2 1/4Cr-1Mo-V, 3Cr-1Mo 3Cr-1Mo-V Steel Heavy
  Wall Pressure Vessels for High Temperature, High
  Pressure Hydrogen Service
• 934-B (initial draft)
• Fabrication Considerations for ¼V Steel Heavy
  Wall Pres Vessels for High Temp, High Pres H2
  Service
• 934-C (final draft)
• Materials and Fabrication Requirements for 1
  1/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for
  High Temperature, High Pressure Hydrogen Service

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Temper Embrittlement Service - Primary Alloys

• 2-1/4Cr-1 Mo 3-Cr-1 Mo
• (API 934 Draft 934-A)
• Enhanced Versions
• 2-1/4Cr-1 Mo-1/4V
• 3Cr-1 Mo-1/4V-Ti-B
• 3Cr-1Mo-1/4V-Cb-Ca
• 1-1/4Cr -1/2Mo (Draft 934-C)
• Others ?
• No techical data available that suggests or
  supports temper embrittlement concerns for weld
  metal in elevated Cr versions
• 5 Cr
• 9 Cr

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Temper Embrittlement

• Phenomena typically occurs at service
  temperatures between 750-1100oF  (399-5930C)
• Segregation of P, As, Sb Sn in the grain
  boundary region
• Results in an upward shift of the
  ductile-to-brittle transition temperature after
  long time exposure   

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J-Factor (Watanabe)

• Base Metal

J ( Si Mn) ( P Sn) x 104 (wt.) Cu
0.20 max Ni 0.30 max (API 934) Mn considered
a cosegregate Mn Si typically lt 1.1 J lt 150
initially, then J lt 120 J lt 100 current
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Weld Metal Toughness Difficulties

• Possibilities
• Reduce pressure at lower temperature
• Use forged rings to eliminate longitudinal seams
• Unacceptable.

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Weld Metal Overcoming Toughness Difficulties

• Control composition
• Heat treatment
• Basicity of electrode coating or flux
• Control grain refinement

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Control Composition Weld Metal

• Residual elements
• P, As, Sb, Sn
• Reducing these elements alone will not ensure
  adequate toughness
• Mn
• Unlike base metal, NOT a cosegregate due to fast
  quench rate
• Necessary for formation of acicular ferrite (
  0.8 ideal)

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X-Factor (Bruscato)Weld Metal

• X (10 P 5 Sb 4 Sn As) (ppm)       
              100
• X lt 20 initial
• X lt 15 current
• Deposit will have maximum resistance to temper
  embrittlement.      

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Heat Treatment Weld Metal

• Example -B3 (2-1/4Cr-1 Mo)
• 12750F (6900C) for 10 hours optimum T1
• 40 ft-lbs 54J_at_ -200F -300C
• PWHT Step Cooling T2

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Weld Metal Coating/Flux Basicity

• Basicity of coating or flux
• Goal Lower Oxygen Content
• Decrease O2, thus SiO2 Inclusions
• Maximizes Toughness
• Bacisity Index (BI) 3.0 Boniszewski
• CaF2 weighted too high

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Grain Refinement Weld Metal

• Temperbead Technique
• 0.080 (2mm) max bead thickness for SMAW
• 0.160 (4mm) max bead thickness for SAW
• 55 KJ max

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Grain Refinement Weld Metal
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Step Cooling Test (API 934)

• 48 Impact specimens
• 24(min.) at Minimum PWHT to Establish Transition
  Curve before Step Cooling
• 24 (min.) at Minimum PWHT PLUS Step-Cooling to
  Establish Transition Curve
• Establish 40 ft-lb (55J) Transition Temperature

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Simulate Temper Embrittlement ? Step Cooling
Test
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Step Cooling Results

• CvTr40 2.5DCvTr40 lt 500F (100C)
• CvTr40 T1 40 ft-lb. (55J) transition
  temperature of the base metal subjected to
  minimum PWHT only.
• DCvTr40 (T2- T1) the shift of the 40 ft-lb.
  (55J) transition temperature of material
  subjected to minimum PWHT plus step cooling heat
  treatment.

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Toughness
CvTr40 2.5DCvTr40 lt 500F (100C) T1
2.5(T2-T1) -6335 -280F, OK
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Weld Metal - Step Cooling Results

• Current Rules
• Only PQR (same trade name, etc.)
• Proposed Draft
• Each lot of electrodes, heat of filler wire, and
  combination of lot of flux and heat of wire shall
  be tested.

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X-Factor (Bruscato)Weld Metal

• X (10 P 5 Sb 4 Sn As) (ppm)       
              100
• X lt 20 initial
• X lt 15 current
• X lt 12 proposed !!!!!
• Bare Wire OK
• SMAW SAW ??????????
• Deposit will have maximum resistance to temper
  embrittlement.      

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API 934, Para.7.2.1.2

• Reference 7.2.1 Welding Procedure Qualification
• The welding electrodes, wire and flux shall be
  of the same type and brand as those used in
  production.
• COMMERCIAL REALITY?

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Consequences of API 7.2.2.1

• Superb, if you are the vendor whose products were
  used to perform the initial welding procedure
  qualifications and, if product is readily
  available.
• Disaster, if you are a fabricator on a tight
  schedule and your vendor ran out of material and
  wont have any available until after you are to
  have shipped the vessel !

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Reality, food for thought

• 50 require same brand as PQR, per API 934
• 50 only require R consumables or those that
  meet X-Factor lt 15 in the deposit

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Consider waiving API 7.2.1.2, If

• GTAW
• X lt 15 of wire on actual size, OK
• SMAW
• X lt 15 in deposit with actual size, OK
• SAW
• X lt 15 in deposit with actual wire flux, OK
• State-of-the-Art suggests that step cooling tests
  should not be requireda chemistry check should
  be adequate

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Summary

• Control composition X lt 15
• Heat treatment 8-10hrs min
• Basicity of electrode coating or flux 3.0
• Control grain refinement via welding technique
  (temperbead)