Pipelines

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Design Codes and Regulatory Requirements

  • Design shall be governed by the most stringent requirements defined by:
    • Local regulations (e.g. MMS – US, HSE – UK)
    • Project requirements
    • Company standards and specifications
    • Local codes and standards

Route Selection

  • Route influenced by
    • Obstructions such as rocks, mud slides, pipelines, platforms, etc.
    • Other users of the seabed
    • Limitations of construction equipment
  • Need detailed survey data to better understand surrounding environment
    • Two main types of route survey:
      • Geophysical - shape of seabed and soil types
      • Geotechnical - strength of seabed soil
    • Survey data are inputs for detailed design and installation

Mechanical Design

Wall Thichness

  • Pressure containment
  • Static and dynamic loading
  • Local buckling (external pressure design)
  • Design codes (U.S. applications)
    • ASME B31.4 (liquid pipeline systems application)
    • ASME B31.8 (gas transportation application)
    • API RP 1111 (hydrocarbons transportation application)
    • Others - Flavor of the region

Wall-Thickness Graph.png

  • Collapse – Bending moment and external pressure

Wall-Thickness Collapse.png

Span Assessment

Span Assessment and Mitigation.png
  • Maximum allowable span length
    • Static stress Analysis
      • Static stress criteria
      • Installation, hydrotest and operation conditions
    • Vortex induced vibration (VIV)
      • Fatigue criteria
      • Operation conditions

Span Mitigation

  • Mitigation strategies:
    • Sandbags
    • Concrete mattresses
    • Structure supports
    • Trenching
    • Rock dumping
    • VIV Suppression - if the maximum span length is governed by VIV and the static stress criteria is satisfied

Thermal Expansion and Buckling

  • Middle-line expansion
  • Upheaval buckling
    • Buried pipelines
  • Lateral buckling
    • Pipeline laid on seabed

Thermal Expansion and Buckling - 1.png

  • End expansion - fixed end vs. free end
  • Pipe burial and rock dumping
  • Thermal expansion loops

Thermal Expansion and Buckling - 2.png

  • Lateral buckling control - buckle initiator
    • Pipeline installed over a sleeper

Elevation View - 1.png

    • Pipeline installed with buoyancy (add to previous)

Elevation View - 2.png

On-Bottom Stability

  • Pipeline stability - Analysis to ensure pipeline
  • Movement is within allowable tolerances for all foreseeable environmental/operational conditions
    • Metocean Data - Design currents and waves
    • Hydrodynamic Forces
      • Drag, Inertial and Lift
    • Soil Lateral Resistance
      • Soil friction
      • Resistance due to pipe embedment
    • Analysis tool (e.g. American Gas Association on-bottom stability program)
  • Mitigation
    • Concrete weight coating or just increase wall thickness
    • Trenching
    • Weight clamps
    • Anchoring

Material Selection

  • Basic Considerations:
    • Strength
      • Pressure
      • Tension
      • Environment
    • Material compatibility with Internal Content
    • Availability of Material
      • Stell, CRA, Flexibles
    • Pipeline Life or Afterlife

Corrosion

  • Types of Corrosion
    • Internal
    • External
  • Mitigation of Corrosion by Coatings
  • Cathodic Protection
  • Internal Corrosion Control

Internal Corrosion Protection

  • Material selection
  • Use corrosion inhibitor chemicals
    • Consider chemical effects on all parts throughout the system
  • Internally coat the line with corrosion resistant material
    • Can be costly
    • May have a limited life
  • Monitor corrosion rate
    • Online corrosion monitoring (corrosion spools, corrosion coupons, iron counts)
    • Intelligent pigging

External Corrosion Protection

  • External corrosion coating
    • Fusion Bonded Epoxy (FBE)
    • Three layer Polyethylene (3LPE)
    • Elastomeric Coatings: Polychloroprene, ethylene propylene diamine (EPDM)
  • Cathodic Protection
    • Must be in a continuous conductive medium
    • Sized to accommodate up to 25% coating breakdown or less over field life
    • May be impressed current or sacrificial anodes

Installation

  • Installation Methods
    • S-Lay Vessel
    • J-Lay Vessel
    • Reel-Lay Vessel

S-Lay Method

S-Lay Method.png

  • Suspended pipe shaped like S-Curve
  • Pipeline must be tensioned to hold its shape & avoid buckling
  • Pipe laying up to 60"
  • 40' or 80' pipe sections welded together horizontally onboard vessel



S-Lay Method - 2.png

J-Lay Method

J-Lay Method.png

  • Suspended pipe shaped like letter "J"
  • Almost vertical tower supports pipe onboard vessel
  • Pipe enters water at high entry angle - no overbend
  • Deep water applications

Reel-Lay Method

  • Pipe is welded together onshore and spooled onto a large diameter reel - plastically yielded
  • Pipe must be straightened offshore during un-spooling


Pipeline Testing and Commissioning

  • Hydrotesting
    • Defined by code, regulation and project requirements
    • Serves as final pipeline integrity check
    • Usually tied to installer's credibility
  • Commissioning is a planned process to prepare the pipeline for operations phrase.