EFFECT AND SIGNIFICANCE OF A CORRECT JOB-SITE SAMPLE
Once the pipe liner has been successfully installed, a job-site sample is generally taken from one of the manhole areas. From this sample, the physical material properties, such as the elastic modulus and the bending strength are determined in an independent, accredited testing laboratory.
The composite wall thickness (backing laminate) of the sample has a decisive role in determining the correct material properties. The composite wall thickness is only the area from the innermost to the outermost glass layer. Pure resin, foil and fleece material are not measured. The outer layer of pure resin must not exceed 20% of the composite wall thickness. Samples that have a thicker outer layer of pure resin should therefore be rejected.
Furthermore, the production surface should not have any pores. Job-site samples with irregularities such as layer shifts or folds are not suitable for testing and do not provide representative results.
The removal of the job-site samples should be carried out with the greatest of care, because the assessment of the complete pipe to see that it meets the performance criteria depends on the results of the sample taken! The job-site sample is thus the reference for the work carried out.
The following standard tests are carried out on the sample sent to the testing laboratory:
THREE POINT BENDING TEST IN ACCORDANCE WITH ISO 178 / EN 13566-4
- Elastic modulus
- Bending strength
- Wall thickness
RING STIFFNESS TEST IN ACCORDANCE WITH EN 1228 / DIN 53768-3
- Circumferential elastic modulus
- Ring stiffness
PROOF OF THE WATER TIGHTNESS OF THE LAMINATE
When cutting the wall, a sample should have up to approximately DN 500 or 8 mm of wall thickness the size of an A4 sheet. For pipe liners with a wall thickness greater than 8 mm, a correspondingly large sample must be taken; the length of the sample should then not exceed 30 cm.
The sample piece is to be marked after it has been taken and immediately stored away from light (for example in aluminium foil). The sample piece is then to be sent to the testing laboratory as soon as possible. If it is not possible to send the sample immediately, care must be taken to ensure that the sample is not stored in a place that is too warm.