process feature | Standards and testing
materials, both commercial and experimental. Pipes of 2in (50mm) diameter were extruded on a laboratory pipe line, and larger pipes were made under ‘commer- cial conditions’. FS tests were performed externally, while S4 tests were carried out in house. “While the FS test is widely understood to be ‘field
representative’, it is cumbersome and expensive to perform,” said Ashish Sukhadia of Chevron Phillips, who presented the results at Antec. “This paved the way for the laboratory-scale S4 test to be developed – but that gave rise to questions about how the S4 test correlated to the FS test.” The two are usually related using a ‘conversion
ratio’. But Sukhadia said that, having tested pipes using both methods over many years, the figure may not be accurate. He suggested that the currently accepted figure, of 3.6, should be in the region of 4.5-5.0. Using a more accurate conversation ratio would
allow S4 testing to be carried out more frequently – and with more confidence, he said. The study also found a link between extrusion rate
and resistance to RCP. “While the exact reasons for improvements in RCP
with rate are not fully understood, we believe that the results may be a combination of relatively higher densities and lower residual stresses in the higher-rate pipes due to viscous heat generation and some level of ‘in-line’ annealing,” said the researchers.
CPVC pipe is increasingly used in hot water applica- tions but is still subject to failure
In hot water Plastic pipe is increasingly used to carry hot water – such as in polymer electrolyte fuel cell (PEFC) or district heating systems. However, it is expensive and difficult to replace this piping if it is damaged – making it more important to predict pipe lifetimes accurately.
Japanese researchers, from organisations including
Kyoto Institute of Technology (KIT), have carried out immersion test on polybutylene (PB) and PEX pipe, to evaluate the effect of residual chlorine on their performance. The study expanded on earlier work by the same
researchers, by extending the exposure time of the pipe, and subjecting the samples to tensile testing and thermal analysis. Pipes were cut in the longitudinal direction, and dumbbell-shaped specimens punched out from these samples. The tests were carried out in 5ppm and 10ppm
residual chlorine solutions at 80, 90 and 98°C for 30,000 hours. For comparison, the same tests were carried out – but with no residual chlorine. Yield stress and enthalpy (internal energy) initially
increased over time in the chlorinated solutions at 80°C, but enthalpy did not decrease at the 30,000th
hour
despite increased yield stress. Elongation at break, however, decreased until the hour – and then either increased (for PB) or hour.
10,000th decreased (for PEX) at the 30,000th
With increasing chlorine concentration, oxidation induction time (OIT) – a measure of thermal stability – for the inner surface of the pipe decreased. The residual chlorine played a key role in suppressing the role of anti-oxidants in the pipe material. Related research – involving the same KIT research-
ers, and also presented at Antec – has used Raman mapping to analyse the crystallinity distribution of polyethylene of raised temperature resistance (PE-RT) in hot water immersion tests. PE-RT is commonly used in hot water pipe applica- tions, and is often preferred to other materials because of its variety and recyclability. “It is important that the degradation mechanism in
hot water is understood for developing higher durablity pipes – but the systematic analysis of these aged samples has not been undertaken so far,” said the researchers. In the study, PE-RT test pieces were immersed in
water at up to 110°C, for up to 12,000 hours. Tensile and thermal properties (using DSC) were measured. The tensile strength increased up to 3000h and, after that, reached a plateau at every test temperature. Tensile elongation at break did not vary much at either 60° or 90°C. Also, elongation at break at 110°C was remarkably reduced up to 12,000h. Raman mapping method was used to examine the
distribution of crystallinity, and found that the degree of dispersion increased over test time from the analysis of Raman peak intensity ratio (crystal to amorphous). The dispersion at 110°C was very high, and showed
42 PIPE & PROFILE EXTRUSION | April 2017
www.pipeandprofile.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58
