RAPID CRACK-PROPAGATION IN SMALL-DIAMETER THERMOPLASTIC PIPE

The S4 (small scale steady state) test, measuring resistance to fast-r unning fracture, is to become a specifying standard for PE gas pipe. T o extend understanding of the method, and to assess its broader useful ness in polymer testing. S4 tests were carried out on commercial 50 mm diameter pipe of 3-6 mm nominal thickness to compare MDPE with ten ot her polymers used in process pipework. Results were normalised, on a h oop stress basis, to a mean radius to thickness ratio of 5 (SDR 11), a nd must also be factored up to estimate any service critical pressure. On this basis, MDPE, with a 0 degrees C S4 critical pressure of 2.8 b ar, was matched by PVDF and slightly bettered by PB. ABS performed ver y well, exceeding 20 bar. PP homopolymer, PA6 and PTFE also out-perfor med MDPE, but PC, modified PVC and PP random copolymer failed to survi ve 2 bar. The critical pressure of POM was too low to measure.