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Close-fitting, socking or relining replacing traditional approaches to pipe renovations


​In recent years, new pipe renovation methods have emerged alongside the old ones, doing away with the need for replacing old pipes. This means cost savings for housing companies, and less inconvenience for residents, who can stay in their apartments during the entire renovation project.

VTT Expert Services Ltd tests new sewerage pipe renovation methods and issues VTT product certificates for them. "The new methods do not require any demolition in the apartment, as detaching the sanitary tapware is usually enough. This makes the methods especially suitable for projects that do not require other renovation in the bathrooms. The methods can be divided into three main categories based on technology: close-fitting , socking and relining", says Product Manager Lina Markelin-Rantala.

Renovated pipes have a service life of 20 to 50 years.

Large pipes can be renovated with the close-fitting method. Socking and relining are suitable for internal piping in the building.

"In close-fitting, a new plastic pipe is installed inside the old pipe. This can be done regardless of the condition of the old pipes. The service life of a pipe renovated with the close-fitting method equals the service life of a new pipe. The expected life of piping renovated with a method tested and certified by VTT is 50 years."

"Socking is a slightly lighter solution. In this method, a sock is inserted in the pipe and coated with material such as epoxy. After the treatment, the pipe has a smooth, hard and durable surface. The durability of different methods has been assessed by ageing the materials used and studying how well they retain their mechanical properties. According to the ageing behaviour of socking materials tested by VTT, they have an estimated service life of 40 years."

"Relining is the lightest renovation method. This method can be used only when the existing piping is in good enough condition. In this method, a new and dense surface is first created with material such as epoxy, according to a pre-specified minimum thickness. The expected life of these methods varies between 20 and 50 years."

Some relining methods produce a pipe that is just as durable and rigid as a pipe constructed with the socking method, so calling these 'relining' may be a little misleading.

Tried and tested methods are certified by VTT

A product certificate issued by VTT indicates that the properties of the components used in the method, as well as the method itself has been tested and assessed by VTT. It is a reliable method.

The product certification process always includes annual quality assurance of the actions of the certificate holder and their on-site installation methods. A product sample is also taken for testing.

"New methods are tested in conditions that stimulate actual conditions. The manufacturer installs their renovation method in the test pipework in our laboratory, which is then tested by running hot and cold water through it following the cycles specified in the test plan. We pay special attention to the durability of extensions and branches as well as adhesion to the pipe," Markelin-Rantala explains.

VTT recommends reviewing and comparing certificates. The methods vary in terms of their suitability to cast iron or plastic sewage pipes as well as their durability and mechanical properties.

Carry out a certificate check

To check whether a method or product is certified by VTT, go to (available in Finnish).


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Fax+358 20 722 7001

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Tel. exchange +358 20 722 111
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Contact us

Tel. +358 20 722 7070
Fax +358 20 722 7001
Opening hours 9:00 - 11:00 and
12:00 - 15:00,
GMT +2 time zone