Pipelines

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

• Collapse – Bending moment and external pressure

Span Assessment

• 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

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

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

• • Pipeline installed with buoyancy (add to previous)

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

• 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

J-Lay Method

• 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

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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.