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Squeeze-off and rerounding of plastic pressure pipes

 

Papers # 2018 Las-Vegas

Within the scope of a DVGW (German Technical and Scientific Association for Gas and Water) research project the technology of squeezing-off for PE pipes at operating pressures higher than 1 bar and the extension to new materials with higher operating pressures were investigated. For this purpose the tightness of the pipes during squeezing and the effects of squeezing on the material properties and the long-term behavior were examined.

The squeezing of plastic pipes [1-4] is a standard shut-off method and safety measure, which is often used in grid operation. Typical uses are repair-, integration- and rerouting measures. Shut-off technologies for plastic piping systems are becoming increasingly important, as gas distribution networks in particular are nowadays mainly designed for plastic piping systems. Due to current material developments plastic pipes are expected to be used in higher pressure ranges (>10 bar) in the foreseeable future. Operational shut-off measures such as squeezing therefore become an indispensable instrument for network operation.

In a DVGW research project three institutes have investigated the method of squeeze-off with regard to gas tightness, applicability at operating pressures > 1 bar and the effects on the continued operation of the pipelines. Pipes made of polyethylene (PE 80, PE 100, PE 100-RC) in various dimensions and pipes made of materials for higher operating pressures (e. g. PA 12, reinforced thermoplastic pipes) were investigated. For the squeezed off pipes the gas tightness was tested by creeping gas measurements up to an operating pressure of 10 bar. Mechanical investigations, creep rupture pressure tests and microscopic examinations were carried out in order to investigate the influence of squeeze-off and rerounding on the integrity of the pipes. Computer tomographic (CT) images were taken to inspect the pipes for defects in the material. The results were used to derive recommendations for practical action, which are currently being incorporated into the DVGW's rules and regulations.

Related keywords : Squeeze-off, Rerounding, Polyethylene, Grid Operation.
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