INTEC provides a full suite of pipeline engineering services for onshore and offshore arctic pipeline systems to encompass the full range of project development and execution including:

• Design Basis Document
• Safety Schematics
• Pipeline Hydraulics and Sizing
• Pipeline Route Selection
• Geohazard Analyses
• Stability analysis and determination of weight coating and/or trenching requirements.
• Determination of pipe wall thickness and steel grade using traditional or limit state design criteria.
• Pipe spanning analyses and determination of pipe support requirements.
• Risk analyses considering anchor risks and other external influences, and definition of remedial measures.
• Platform/structure tie-in analyses.
• Shore crossing studies to determine most cost effective method to install a pipeline in this very dynamic region and provide necessary protection.
• Pipeline installation studies to verify multiple installation options, which can be maintained for cost and contractor competitiveness.
• Material Specifications
• Construction Specifications
• Route Drawings

There are several aspects of pipeline design in arctic regions or arctic environments, which offer additional challenges to the designer.  Some unique aspects of arctic designs conducted by INTEC include pipeline environmental loadings and the effective use of limit state design for extreme loading conditions resulting from ice scour.

Ice Scour

Ice scour or gouging of the seafloor is a near-shore feature for most of the northern continents.  Sea ice is driven by wind and current forces and tends to pile up creating a pressure ridge.  This pressure ridge has a keel extending below the water surface and it moves with the ice sheet.  Occasionally, these ice keels intrude into water with depths less than the ice keel draft and form a gouge in the seafloor soils.  A pipeline on the seafloor in such an environment may not be able to withstand the ice contact loadings and typically must be buried below predicted extreme ice keel scour depths for protection.  Further, the pipe must be trenched sufficiently far beneath the influence zone of soil displaced below the ice keel to limit pipe bending to acceptable limits.

Permafrost

An Offshore pipeline transporting oil or gas to shore will need to transition through a shore crossing.  In some arctic applications, the shore crossing will have soil ice-bonded permafrost underlying the pipeline.  When the pipeline becomes operational, the temperature of the pipeline will typically increase warm surrounding soil and create a permafrost thaw bulb.  This may result in permafrost thaw consolidation and pipeline settlement.  If the settlement area is adjacent to an area, which is thaw stable, the result is a highly loaded pipeline span.  This differential settlement can induce considerable bending strain in the pipeline and must be accounted for in design.

Temperature Effects

When a pipeline is operated at a temperature higher than the ambient temperature during installation, the pipeline will attempt to expand longitudinally (thermal expansion).  A long pipeline in contact with the soil, buried or unburied, is not entirely free to expand due to the restraint provided by the surrounding soil.  This can lead to excessive axial compressive forces and upheaval buckling if not adequately addressed by the pipeline design and construction procedures.

Strudel Scour

Nearshore arctic zones typically develop a bottomfast ice sheet during the winter season.  If an onshore river flow encounters such an area during the spring breakup, the river water will overflow the bottomfast ice sheet in the nearshore zone.  This overflow water will spread offshore and drain through cracks or holes in the ice sheet.  If the drainage rate is high, hydrodynamics (high velocity currents) at the seafloor can scour seabed sediment and potentially expose and impose high current loads on a pipeline.  This phenomenon is known as strudel scour and may result in unacceptable pipeline spans.

Limit State Design Application

Limit state design applications for an above ground arctic onshore pipeline may include internal pressure, wind-induced vortex induced vibration (VIV), corrosion and expansion (due to warm pipe contents).  Limit state design applications for offshore buried arctic pipelines may include internal pressure, ovalization (due to displacement controlled bending) and unstable weld flaw propagation due to tensile bending strains.  In previous designs by INTEC, multiple limit state applications have been developed for pipe behavior during extreme bending.  INTEC has conducted full-scale bend test programs on behalf clients to quantify these effects and validate design by confirming ultimate design strains.