Pipelines on Permafrost: Why They Are Raised on Supports and How the Ground Is Protected

The problem

Permafrost is ground that stays frozen all year round. While frozen, it is strong. But if it is warmed, the ice in its pores melts, the ground turns into mud and settles.

A hot pipeline laid directly in the ground acts as a heater: a thaw zone forms under it, the pipe shifts, supports settle, and the welds take loads they were not designed for.

Two design principles

Construction on frozen ground follows one of two principles set out in the Russian code SP 25.13330 "Foundations on permafrost soils":

Principle I — the foundation ground is kept frozen for the entire service life;
Principle II — thawing is allowed, but its settlement is accounted for in advance.

For hot pipelines on frozen ground, the first principle is chosen most often — the ground is left undisturbed.

Why pipes are raised on supports

The most reliable way to preserve permafrost is to raise the pipe above the ground. A ventilated space remains between the pipe and the ground: heat goes into the air, not into the soil.

Supports stand on piles driven into the frozen ground below the layer that thaws in summer. Depth matters: in this layer, frost heave in winter tries to push the pile upward.

Ground thermosiphons

A thermosiphon is a sealed tube with a refrigerant: its lower part goes into the ground, and its finned upper part sits in the air. In winter the refrigerant evaporates at the bottom, rises and releases heat to the cold air, and the condensate flows back. This way the device pumps heat out of the ground all winter without electricity.

In summer, when the air is warmer than the ground, the thermosiphon switches itself off. On critical supports they are mounted directly on the piles.

Pipeline supports on piles with ground thermosiphons in the tundra — Thermosiphons on piles remove heat from the ground in winter and keep it frozen.

Compensating temperature differences

A northern pipeline is installed in summer, may cool to −50 °C in winter, and the product inside may be hot. A difference of hundreds of degrees causes huge expansion that has to be absorbed:

a zigzag route — the pipe follows a broken line, and expansion goes into the bends;
U-loops and bellows expansion joints — where the route is straight;
sliding supports on which the pipe moves freely.

You can calculate expansion for northern temperatures in our calculator.

We supply expansion joints, supports and valves for northern sites — designed for frosts down to −60 °C.

Expansion joints catalogue

Insulation and heating

Pipelines carrying water and viscous products are protected from frost with thick thermal insulation and a protective jacket and are heated by heat tracing cable or a steam tracer. Materials and equipment are selected for frosts down to −60 °C: ordinary steel and seals become brittle at such temperatures.

Monitoring

Permafrost changes over time, so it is monitored: ground temperature is measured in thermometric boreholes, and surveyors check the position of the supports. If the ground under a support starts to thaw, it is visible in advance — before the pipe shifts.

FAQ

Why are pipes not buried in the North?

A hot pipe in the ground thaws the permafrost, the ground settles, and the pipeline deforms. Above ground, heat goes into the air and the ground stays frozen.

What is a ground thermosiphon?

A sealed tube with a refrigerant that removes heat from the ground into the air in winter without electricity and keeps the ground frozen. In summer it stops working by itself.

Why are pipelines laid in a zigzag?

Bends in the route take up thermal expansion. In the North the temperature range is very large, and a zigzag helps absorb expansion without many expansion joints.

What steel is needed for Arctic pipelines?

Cold-resistant steel that keeps its toughness at low temperatures. The grade is chosen by the minimum operating temperature and calculation; ordinary carbon steel becomes brittle in severe frost.

Why is a pile error dangerous?

If piles did not reach strong frozen ground or bedrock, they settle unevenly when the ground thaws, and the supports give way under the structure. Such errors have caused major accidents in the North.