Tillfällig avstängning av plaströrsledningar genom sammanklämning - kunskapsläge

• Temporary closure of plastic pipes by squeeze-off - state of the art State of the art and present use of squeeze-off methods for temporary closure of polymer pipelines for water and gas was investigated by an enquiry and a literature study. A limited, supplementary series of tests was also performed. The aim was to find, if possible, general limitations for use in terms of temperature at squeezing, pipe dimensions and materials, and to identify important problems that have to be analysed before guidelines can be issued regarding the use of the method. Some producers, suppliers and users in Sweden, were interviewed by the aid of a questionnaire. Although the investigation was limited, the answers are so homogeneous that they are considered representative. The belief is that the technique is harmful. It is used mostly for PE 80 and PE 100 materials and when necessary, e. g. when no valves are available. Decisions and risk assessments are mostly made ad hoc. The performance is according to manuals from producers and suppliers. Design of equipment, geometry, and recommended squeeze rates varies among suppliers. The literature on pipes consists mainly of papers from the 80-ies and 90-ies and from some research groups in the USA. There is a heuristic knowledge about formation and appearance of damage, and to some extent about the influence on service life. Newer research on general damage and fracture in polymers is available that is not related to the specific conditions in squeezed pipes. Such models are lacking, which may be due to the complexity of the area and its hands-on character. The commonly used PE 80 and PE 100 materials are clearly damaged by squeezing, particularly so for high compression levels, but the pipes still fulfil the requirements for use. Stronger and more crystalline materials, and larger pipe sizes, seem to be more severely damaged. It is not known how the damages influence slow crack growth and life. Squeeze-off on PE pipes with external longitudinal scratches should strictly be avoided. Also squeeze-off on PE pipes with PP coating at low temperature should be conducted with precaution until the opposite have been proven as some damage cases were reported. Removing the PP coating is recommended by some in this case. The experiments, on one old PE 80 pipe and two new PE 100 pipes with dimensions from 315 to 355 mm confirm the picture of damage. Commercial equipment was used and according to the supplier’s manual. All the pipes show similar damage, with crack formation and unevenness. Those are less significant for thinner pipe walls than for thicker ones. There is no apparent difference between new and old pipes. A few pressure tests were carried out on the squeezed pipes as well as the untouched pipes. The results show that no significant reduction of the lifetime could be proven regardless when an interrelated comparison between a squeezes and not squeezed pipe was made or when the lifetimes were compared with those obtained in earlier available material classification tests for the actual materials.

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