Assessment of the condition of the district heating systems can be extremely important to a local authority’s decision to implement urban renewal projects.

Prior to undertaking urban renewal the condition of the district heating systems should be assessed. Based on this assessment, it can be established whether the district heating system has a service life similar to the life of the urban renewal measures or whether within the foreseeable future an increased number of leaks and the need for excavations and the replacement of piping may be expected.

As an important tool for use in local authority decision making processes FORCE Technology offers to perform such assessments of district heating systems.

An assessment of a district heating system may include:

• Selection of locations where Long Range ultrasonic measurements can be made.
• Visual inspection of service pipes, socket joints etc, possibly compared to information on previously performed repairs in the area and the reasons for these.
• Assessment of the water quality in the district heating system based on analyses carried out by district heating system operating personnel or by an external laboratory.

Reliable, well-considered decisions

The Municipality of Kalundborg utilised FORCE Technology’s expertise within the inspection of district heating systems in their decision making process.

The municipality is facing having to renovate a total area of about 68,000 m2 in the town centre, and in this context wished to ensure that the underlying district heating system was of high enough quality not to trigger a need for comprehensive replacement of piping within the next 20 years.

Random sampling of the district heating network

In the Municipality of Kalundborg, the course of action was as follows: FORCE Technology’s experts in ultrasonic testing, visual inspection and corrosion selected six different locations in the piping network where ultrasonic testing should be performed.

The tests examined both supply and return pipes. Thus the condition of the district heating system was determined at 12 position in 6 excavations.

In addition, copper service pipes were visually assessed at the entrance to three residences. The visual assessment of service pipes was performed on both supply and return pipes, so service pipes were assessed at a total of six locations.

The piping insulation was also examined through visual assessments of socket joints on sheath pipes around the welded joints. In the Municipality of Kalundborg socket joints consist of steel sockets, which is a commonly used method of jointing. Subsequent to mounting, the joints were filled with expanding foam.

In the experience of FORCE Technology socket joints can be one of the most critical components in a district heating system.

Finally the water quality in the district heating system was assessed. The quality of water was documented through analyses performed by an external laboratory.

Extremely rapid testing technique

The Engineering Department of the Municipality of Kalundborg was responsible for excavations around pipes. Due to the use of the Long Range ultrasonic technique – which “shoots” ultrasonic waves up along the pipe – it was only necessary top expose just over 1 metre of pipe for FORCE Technology to perform measurements up to 50 metres in each direction.

The technique has been developed for use on stretches of pipe which are not accessible due to their being buried, covered in insulation, located high up, at lead-ins, etc, and can be used on hot surfaces and piping in use. Therefore the method is particularly appropriate for use in condition checks and residual service life checks of district heating pipes.

The project including excavation, inspection and restoration of insulation had to be carried out extremely quickly, as the town of Kalundborg was expecting visitors from a cruise liner and it was important to quickly restore the town to a presentable condition. FORCE Technology’s specialists had five days to carry out the inspection, but took only two, as everything went according to plan.

The district heating pipes are good for another 20 years

In conclusion, FORCE Technology’s ultrasonic testing of the Municipality of Kalundborg’s district heating system detected no critical reductions in the piping wall thickness, nor did visual inspection of the service pipes find any signs of external corrosion.

A visual inspection of the socket joints found some joints with incipient corrosion, but the corrosion speed was assessed as being so low that given unchanged conditions corrosion would not penetrate within the next 20 years.

For the future monitoring of corrosion conditions in the system, FORCE Technology has recommended the establishment of a continuous corrosion monitoring system.