Alaska Gas Pipeline A Technical Brief

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Alaska Gas PipelineA Technical Brief
Joy O. Kadnar
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Alaska Gas Resources Major Producers

• Known resource 35 Tcf
• Prudhoe Bay 8 Bcf/d of production
• Ultimate estimates 100 Tcf

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Overall Project Scope
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Alaska Gas Project Overview
Producers recently completed a US125 million
study to assess cost, technology, regulatory, and
environmental issues

• Alaskas North Slope has substantial gas
  resources 35 TCF discovered, 100 TCF potential
• Transportation is the main cost - a buried
  pipeline is the most efficient way to market
• Either Northern or Southern routes can be safely
  built and operated.
• Costs approximately US20 billion
• Toll to continental markets is approximately
  US2.39/mcf for either route
• Alaska law, federal Energy Bill provision, ACT
  and environmental groups all mandate the Southern
  route

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Alaska Natural Gas Pipeline ActSigned into Law
on 10/13/04

• Established Federal Coordinator
• No Over-the-Top route
• Public Need Downstream capacity is presumed
• Loan Guarantee Program was established
• There are provisions for an Alternate
  Construction Study
• FERC is Lead Environmental Agency and must issue
  Open-Season Rules in four months

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FERCs Actions

• Hosted technical conference on December 3.
• Initiated a rulemaking to establish regulations
  governing the conduct of open seasons for
  capacity on any Alaska natural gas transportation
  projects.
• Written comments on the NOPR are required to be
  submitted by December 17, 2004.
• Regulations will be issued by February 10 next
  year, i.e., within 120 days of enactment of the
  Act.

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Design Estimates (Alaska to L-48)
Gas Treatment Plant
Pipeline (AK-gtCA)
NGL Plant
Pipeline (CA-.US)

• Pipeline Design Rate (bcfd) 4-6
• Expansion Potential (bcfd ) TBD
• Compressor Stations 25 - 30
• Total Pipeline Horsepower 1.2 1.4 million
• Alaska to Alberta (miles) 1,800 - 2,100
• Alberta to Market (miles) 1,500
• Pipe Diameter (inches) 52
• Operating Pressure (psi) gt2,000
• Tons of Steel 5 6 million
• Construction Staff-Hours gt50 million

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Project Challenges

• Mill capability and capacity (volume)
• Consistently meeting material specification
• Welding productivity
• Fracture propagation and control
• Defect tolerance of welds
• Tensile and compressive strain limits
• Bending

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High Strength Steels Standards

• Until recently, HSS was a non-standard grade of
  material
• Canadian Standards CSA-Z245 standardized grade
  690 in 2002 revision.
• A New Work Item was proposed at API Tubular Goods
  Meeting in Vancouver, BC in January 2002 to
  include grades X90, X100 and X120 in future
  revision of API 5L.
• The API NWI was proposed by Exxon-Mobil and
  supported by BP
• BP has drafted a proposal for a NWI to ISO
  TC67/SC2 for Grade L690 (X100) to be included in
  revision of ISO Standard 3183 - Linepipe

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Required Material Properties

• Lean composition but with high strength
  toughness
• High Charpy toughness and CTOD at low temperature
• High longitudinal toughness for arrest of running
  ductile fracture
• YS/TS ratio values may be above 0.90
• High strength and toughness requirement in
  longitudinal seam weld in high heat input
  submerged arc welds high alloy
• Toughness and strength of seam weld HAZ

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HSS Constructability Issues

• Steel Lean composition for toughness
  weldability
• Measurement of strength longitudinal
  transverse
• Field bending characteristics and weldability
• Welding consumables and girth weld properties
• Main line and tie-in welds
• Resistance of thin wall to denting in the field

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Some Findings

• Mechanised GMAW trials indicate that HSS line
  pipe is weldable
• Welding can be accomplished with commercially
  available welding consumables.
• New consumable development is in progress
• Adequate weld metal strength and toughness is
  achievable
• Weld metals are more sensitive to welding process
  or parameter variations than lower grades of
  pipe.
• Precision is needed in control of the welding
  process.

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Fracture Control on HSS

• Traditional approach to control of propagating
  fractures not appropriate
• Toughness requirements beyond manufacturers
  capability
• Crack arrestors required (steel grouted sleeve,
  composite reinforced line pipe, other?)
• Modelling work to predicted design requirements
• Full-scale test had to be conducted

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Fitness-for-purpose Considerations
Type of defect FFP methods applicability? Gap / problem Way forward
Corrosion No (methods not applicable due to grade limits) Model is governed by plastic collapse but is unproven for X100. Tests on X100. ensure ductile material behaviour (not in API 5l).
Gouges, manufacturing defects Yes BS 7910, API 579 NG-18 (Battelle) not applicable due to wall thickness and grade limits. Limited tests on X80, and wall thicknesses up to 20mm. Flow stress dependent method. Tests on gouged pipe with the pipeline parameters.
Girth weld defects yes BS 7910, API 579. EPRG not applicable due to wall thickness and grade limits. Use of BS 7910 or API 579 needs fracture toughness data. Fracture mechanics testing or wide plate testing.
Cracking Yes BS 7910, API 579. Use of BS 7910 or API 579 needs fracture toughness data. Fracture mechanics testing.
Corrosion, gouges and cracking (fatigue) Yes BS 7910, API 579. Use of BS 7910 or API 579 needs fracture toughness data. Fracture mechanics testing.