Steel posts in earth

Test pilings reveal rate of corrosion

Steel pilings used for infrastructure corrode at different rates depending on what soil they are exposed to. After 30 years, test pilings have been unearthed for study and the results are important for the Swedish Transport Administration.

A large part of today’s infrastructure is below ground. This includes water and sewerage lines, culverts and steel pilings that provide stability for houses or infrastructure. Water, pH and various types of soil are just some of the factors that affect how materials corrode.

Corrosion in different types of soil

Swerea has performed a corrosion study of steel pilings exposed to different types of soil. The results have shown that certain parts of steel pilings exposed to muddy clay corrode at a rate of 18 micrometres each year. This number has significance for guidelines for corrosion allowance.

Steel pilings are made thicker than necessary to have a margin for corrosion. There are different types of guidelines for corrosion allowance. One is based on a European standard and in certain cases a corrosion rate of 12 micrometres per year has been previously stated.

New knowledge for corrosion protection

Several projects for developing new guidelines and expanding knowledge of corrosion protection in various environments have been underway for about 30 years.

Swerea initiated an exposure study with various soils in the 1980s to investigate how corrosivity varied. The knowledge is important for the Swedish Transport Administration, which is responsible for building and tending to roads and railways.

Besides the results for corrosion allowance, a Swerea project also showed that the rate of corrosion can be categorised into two groups, depending on the soil type. This type of grouping was previously known about, but has now been confirmed in more detail.