It is important that the gap is as small as possible because it only consists of air, steals space and can cause problems with leakage of groundwater.
The engineering office Siebert + Knipschild GmbH has determined the mean ring gap between the old pipe and a CIPP hose liner from Inpipe Sweden AB.
The smaller the gap, the better!

The company Inpipe Sweden AB commissioned the engineering office Siebert + Knipschild GmbH to determine the mean ring gap between the old pipe and the CIPP hose liner on a pipe section supplied by the client.

The sample material provided to us was a ring section of a CIPP hose liner in a shell pipe with a diameter of approx. DN 225. The length of the ring section was approx. 50 cm. The shell pipe was a steel pipe with a wall thickness of approx. 3 mm. The cured CIPP liner inside had a wall thickness of approx. 3 mm.

In order to determine any gap between the shell pipe and the CIPP liner the ring gap is measured in twelve positions with an offset of 30° between them. The ring gap is determined on both cutting surfaces using a feeler gauge (scaling 0,05 mm). The diameter of the shell pipe is determined all around in 60° intervals in line with DIN EN 1228.

Fig. 1 and Fig show the ring section with marks for the measuring spots on both sides.

The gap was determined acc. To DWA-A 143-2 “Static Calculations for the Rehabilitation of Sewers and Sewage Pipelines with Lining and Installation Procedures.”

On a ring section we determined the ring gap between an INPIPE liner and a steel pipe. On the basis of the measured results we can derive information on the shrinkage behavior of the hose liner when in cures.

The static calculations on the rehabilitation of sewers and sewage pipelines by hose lining were made acc. to DWA-A 143-2. Before the start of rehabilitation a theoretical gap formation of ωs = 0.5 % is assumed as a safety parameter. During installation after inflation the liner shall be in full contact with the old pipe and shall not leave a planned gap. The ring gap to be taken into account in static calculations results from the thermal and chemical shrinkage of the resin system.

On the INPIPE liner in a steel shell pipe that was provides as sample material we could not determine any ring gap nor gap formation. The hose liner is in full contact with the shell pipe.

Oststeinbek, January 11, 2022

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