Over the years there has been an increasing trend for resource companies to develop mining projects in cold regions and areas of permafrost. The arctic presents unique engineering challenges. Many of the sites are in remote areas where road access is difficult. These regions bring about challenges related to labour, equipment, logistics and costs. This discussion is intended to highlight arctic pipeline engineering design considerations.
Arctic Climate Tailings Pipeline (photo credit: Mazyar Jalayer)
In the arctic, the upper ground layer will go through seasonal freezing and thawing. Below the upper layer lies the permafrost, a layer of soil that remains frozen throughout all the seasons of the year. In some areas, the permafrost extends to the top of the soil and the soil remains permanently frozen. The permafrost makes excavating during construction a challenge. Furthermore, if permafrost is exposed to warm air, it will degrade, which compromises the structural integrity or load bearing capacity of the soil.
When piping materials become cold they lose their ductility and exhibit brittle behavior. It is important therefore to design structures with materials that retain their ductility in freezing environments. Ductile materials tend to yield before failure. The yielding of the material is important for two reasons: the material shows signs of failure which reduces the chance of a catastrophic failure and, ductile materials can absorb more energy upon failure. When the temperature of a material is lowered, the material becomes less ductile, transitioning to a brittle state. Failure of brittle material could be catastrophic and without any warning. It is important to utilize tough materials for structural components or for pressure retaining equipment operating under low temperatures.
The effect of cold temperatures must also be considered when welding metals together. The heating and cooling (quenching) which happens during welding can have significant effects on the material microstructure. It is important to utilize welding procedures that are appropriate for cold temperature applications.
On the left cup-and-cone fracture (ductile material), on the right, brittle fracture
(photo credit: Dan Kay & Associates)
The ability to completely drain a pipeline of its contents is critical in cold weather climates. Where possible, pipelines should be graded such that the fluid drains by gravity following a water flush. Any low points should include a drain valve. Alternatively, a pigging system could be installed on the pipeline to allow a compressed air-propelled pig to remove the remaining water in the pipeline following a flush.
Piping and equipment may require winterization to prevent freezing and damage to the equipment. In permafrost regions, insulated pipe requires special attention since insulation is used to ensure against pipeline freezing or permafrost degradation. In extreme cases the pipe will need to be raised above the ground to prevent heat transfer from the pipe to the ground below.
It is important to note that waterproofing of the insulation and heat tracing components is vital to overall pipeline performance. If moisture is allowed to penetrate the insulation jacket, the freezing of the water can damage the insulation and render it ineffective.
Extreme example (Alaska pipeline), placed high above the ground on pillars to prevent heat transfer to the soil,
heat pipes direct the flow of heat to radiators placed above the pillars to dissipate the heat
(photo credit: Rose, RoadsideAmerica.com)
There is an increasing trend towards the use of pre-insulated piping as a solution for cold region piping systems. Pre-insulated pipe offers a cost-effective solution to expensive field insulated pipe. Pre-insulated pipe consists of a core carrier pipe (carbon steel or HDPE), an insulation layer and an outer HDPE pipe jacket for weatherproofing. Pre-insulated piping can sometimes be supplied complete with heat trace channels.
Another consideration in the arctic region is the design of the heat trace system which is used to safeguard against freezing and provide a means to thaw a frozen pipeline. The designer must pay careful attention to pipeline heat transfer to the working fluid and the permafrost.
Due to the large fluctuation in temperature between the summer and winter months in the arctic climate, thermal expansion and contraction is another parameter that should be carefully considered. Carbon steel pipes should be carefully anchored to prevent excessive thermal load which may cause the pipe to buckle. Plastic and stainless-steel pipes also require careful analysis because of their high thermal expansion coefficient. Jacketed, or pre-insulated pipe will also require careful consideration; thermal expansion of the carrier pipe may differ from that of the protective jacket. The thermal effect of sunlight on exposed pipelines is also important to understand.
Expansion Loop pipe (pre-insulated pipeline) (photo credit: VHM Solutions Pty LTD)
This article discusses some of the main challenges to be taken into consideration in the engineering design and implementation of pipelines in the arctic. Each location and project will present its own unique set of challenges and will require innovative pipeline solutions as the resource industry extends itself further into remote arctic regions.
About The Author
BASc (Mech Eng), MASc Eng (Mech Eng), P.Eng, PE
Mazyar Jalayer is a Project Engineer at Paterson & Cooke’s Vancouver office. He joined the company in 2011 and has thirteen years of EPCM experience in projects related to mining and mineral, oil and gas, hydrotransport, and piping and process. He has worked on a variety of projects from front end engineering design through to detail engineering phase. He specializes in Arctic engineering design, slurry pumping system, plant and piping design.
Mazyar has a Master of Applied Science degree in Mechanical Engineering (Thermo-Fluids) from the University of British Columbia. He is also registered as professional engineer in both Canada (P.Eng) and USA (PE).