Papers
Plastic Pipes Conference Association # 2016 Berlin
David Chrystie-Lowe
The many benefits of PE100 pipe materials include flexibility and toughness in addition to being relatively light products that are not subject to corrosion and expected to last well beyond the design lifetime [1]. It is also a distinct advantage that end-load resistant joints can be made using butt fusion (BF) and electrofusion (EF) welding. There is, of course, always room for improvement and Exova has continually provided solutions to the difficulties identified for both BF and EF welding processes [2, 3]. In addition to the new training standard reported at the last conference [4] that is expected to result in a step change in improvement of site practice, Exova is active in a variety of other ways to ensure that quality is assured as now presented.
Development of BF welding conditions and testing has been previously been reported by Exova [4, 5] and Beech et al [6-9] in recent conferences. The latter work was funded by the PE100+ resin producers and completed in collaboration with other laboratories. Results have been used to harmonise conditions within ISO 21307 [10], but the work was incomplete as highlighted by Striplin et al [11].
Exova therefore undertook further work to consider the influence of ambient conditions on the BF welding process, which included consideration of forced cooling in an attempt to reduce the duration of the welding cycle. The range of pipe wall thickness that may be welded was also extended. This included consideration of all welding conditions within ISO21307 in addition to those used by the gas industry in the UK [12]. Consideration was also given to the accommodation of thick section welds within test methods. In addition to short term testing, long term and non-destructive testing has been used to report on the quality of welds produced over a wide thickness range (30- 90mm) and in 4 different welding conditions. Although ambitious, the project has resulted in significant achievements and provides a new baseline for both welding conditions and testing in the future.
End-user stakeholders of the pipe materials have requested more realistic test methods that enable better understanding of the performance of the products, both in terms of type testing of EF fittings and quality control of joints in the field. The approach that Exova would recommend includes a performance type test based upon resistance to contamination, first introduced in the UK decades ago [13] and hailed by local manufacturers as a breakthrough. The second consideration is the availability of adequate handling equipment, notably clamps, especially for coiled pipe [14, 15]. Although pressure testing may be used for type tests, quality control tests need to be more practical and a shear test has been developed that relates directly to service performance of the joint [16]. Finally, modern NDT methods based upon microwave and phased array ultrasound has been established to provide the best non-destructive indication of long term performance [17-18].
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