Metal at −50 °C: Cold Brittleness and Steels for the North

What cold brittleness is

As temperature drops, many steels lose toughness. Above a certain limit, overloaded metal first stretches and bends — a ductile fracture. Below it, the metal splits with almost no deformation — a brittle fracture. This limit is called the ductile-to-brittle transition temperature.

A brittle crack runs very fast and can travel a long way along a pipe or tank. For the North, therefore, not only steel strength matters but also its behaviour in frost.

Brittle and ductile fracture of steel in frost — Left — brittle fracture: flat and grainy. Right — ductile: the metal stretched and tore.

How it is tested: impact toughness

Susceptibility to brittle fracture is assessed by the notched-bar impact test per GOST 9454: a notched specimen is broken by a pendulum at a set sub-zero temperature and the absorbed energy — the impact toughness (KCU, KCV) — is measured.

In mill certificates for northern projects, check at what temperature impact toughness is confirmed. A steel with good values at +20 °C may not be suitable for −50 °C.

Steels used in the North

Material	Behaviour in frost	Where it is used
Ordinary-quality carbon steels	Relatively high transition temperature	Outdoor structures in the North — limited use, by calculation only
Low-alloy 09G2S	Retains toughness at low temperatures	Pipelines, tanks, steel structures, flanges for cold climates
Austenitic stainless 12Kh18N10T	Not prone to cold brittleness, tough in severe frost	Expansion joint bellows, valves, equipment for aggressive media

The final material choice is confirmed by calculation and the project's minimum temperature requirements.

KhL design

Equipment for cold climates is produced in climatic design KhL or UKhL per GOST 15150. It covers not only body materials but also seals, lubricants and rubber parts — they also lose properties in frost.

What matters in practice

Do not hit frozen pipes and valves with a sledgehammer — an impact in frost can split the metal.
Avoid stress concentrators: abrupt transitions, lack of fusion, notches.
Weld using procedures qualified for low temperatures, with weld inspection.
Check that certificates confirm impact toughness at a temperature no higher than the minimum operating temperature.

We supply pipes, flanges, expansion joints and valves in northern design.

Equipment catalogue

FAQ

Why do pipes crack in frost?

Below the transition temperature steel loses toughness and fails in a brittle manner — from an impact, overload or stress concentrator.

Which steel is suitable for −50 °C?

Low-alloy 09G2S or austenitic stainless steels are typically used; the choice is confirmed by calculation and a certificate with impact toughness at the required temperature.

What is the KhL design?

A climatic design for cold climates per GOST 15150: materials, seals and lubricants are rated for low temperatures.

What does impact toughness show?

How much energy the metal absorbs when a notched specimen is broken by impact. The higher the value at low temperature, the lower the risk of brittle fracture.