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Are methods for tightness testing fit for purpose?

 

Posters # 2012 Barcelona

Problems sometimes occur in tightness testing of plastic pipelines using pressurized water and accounting for the diametrical expansion, particularly so for larger sizes and higher pressure rating. Pipelines that are in fact tight enough for acceptance are rejected when first tested. A study consisting of two parts has been carried out in order to find the cause of the problems and suggest suitable actions. The first part was an enquiry directed towards users of pipelines and firms performing tightness testing. The objective was to find out about the practical performance of testing and the experience from it. The second part of the study was a scrutiny of a number of methods used in Sweden, Norway, USA, Finland, Germany, and Great Britain. The general problem is to distinguish, by measuring pressure or volume over time, on one hand the leakage and on the other hand the time-dependent expansion of the pipeline. The principles used have weaknesses e g in terms of sensitivity, which may be pronounced when new types of material and designs are introduced. The main conclusions are (1) the risk for accumulation of several minor errors in performance, as e g calibration, means that test performers should revise and update working procedures, and if need be to introduce a quality assurance system, (2) if, for European harmonisation, it is wished to introduce the EN 805 generally, this method should be assessed more carefully and revised. An indication is that substantial national modifications have been made in at least Norway and Germany and (3) the quality assurance can be facilitated by further education of operators and that calibrated equipment with high accuracy are used. The Swedish method has several advantages. If it is to be used in the future it should, however, be modified. One simple way would be to increase the accepted leak flow for larger sizes and thinner pipe walls, in order to diminish the sensitivity of the method for these.

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