Decompression wave speed and crack velocity measurements during S4 test in water pressurized plastic pipes: Part 2. Criteria for onset of rapid crack propagation

Abstract

The rapid crack propagation behavior in pressurized plastic pipes was investigated to establish the criteria for onset of rapid crack propagation in terms of the relationship between decompression wave speed and crack velocity. The study was performed by using an instrumented S4 test apparatus, the methodology for which is described in Part 1 of this paper. To establish the criteria for the onset of rapid crack propagation in water-filled plastic pipes, PVC pipes of 440 mm outside diameter having dimensional ratios of 14, 18 and 25 were tested following the procedure described in ISO 13477. From the measurements made on decompression wave speed and crack velocity, it was determined that, for rapid crack propagation to occur in the S4 test, two conditions were required. The decompression wave speed, Cw,S4, needs to be lower than the rapid crack velocity, a˙. Also, the crack velocity must be equal to or above the critical crack velocity, a˙crit. That is,Cw,S4≤a˙a˙≥a˙critIt was shown that this critical crack velocity is always greater than the theoretical decompression wave speed in water filled pipes. Until now, the criterion for rapid crack propagation in S4 was understood to only involve the former condition in water pipes. With this and the latter condition proposed, more complete criteria for rapid crack propagation in water filled plastic pipes using the S4 method is now established.