Polyethylene Close-fit-liner – Material Properties and Long-Term Failure Behavior

Session 5A
11:20

Anita Redhead, Polymer Competence Center Leoben

For cost-saving and efficient trenchless pipe rehabilitation the technology of polyethylene Close-Fit-Liners has been used successfully for many years. Conventionally extruded pipes are folded immediately after extrusion to reduce the cross section, inserted into the old or damaged pipe and finally redeformed using the memory-effect which is typical for thermoplastics materials.

In contrast to a conventionally plastic pipe the folding process to the Close-Fit-Liner (CFL) and the redeformation during installation implies a considerable additional mechanical and thermal load on the material. With respect to a sustainable pipe rehabilitation and guaranteed operating times of 50 years and even more, the question of changes in the material properties is more than justified.

Within the presented work a comprehensive material characterization of a commercially available PE 100 CFL was done. The focus was put on a comparison of the unfolded conventionally pipe to the final state of the redeformed CFL. In addition to an optical surface characterization mainly the morphological investigation of crystallinity and molecular orientation enhances the understanding of the typical character of this installation technology. The evaluation of thermo-oxidative material aging confirms that the additional thermal exposure
has no negative effect on the material stabilization. However, a significant reduction of the residual pipe stresses was detected. To estimate changes in the long-term failure behavior the resistance against crack initiation and slow crack growth was characterized and longer failure times for the undeformed pipe and the redeformed CFL were measured. This was also confirmed by internal pressure creep rupture tests.

The presented results confirm that relevant material properties are not affected negatively by the additional deformation and redeformation processes typical for the CFL technology and that all in all an improved long-term behavior is to be expected.

A. Frank (1), A. Hofmann (2), M. Haager (3), G. Pinter (4)
1) Polymer Competence Center Leoben GmbH, Austria
2) Rabmer Bau- und Installations GmbH & Co KG, Altenberg, Austria
3) AGRU Kunststofftechnik GmbH, Bad Hall, Austria
4) Institute of Materials Science and Testing of Plastics, University of Leoben, Austria