Rapid crack propagation, as its name implies, is a very fast fracture. Crack speeds up to 600 ft/sec have been measured. These fast cracks can also travel long distances, even hundreds of feet. The DuPont Company had two RCP incidents with its high-density PE pipe, one that traveled about 300 feet and the other that traveled about 800 feet.

RCP cracks usually initiate at internal defects during an impact or impulse event. They generally occur in pressurized systems with enough stored energy to drive the crack faster than the energy is released. Based on several years of RCP research, whether an RCP failure occurs in pipe depends on several factors:

Typical features of an RCP crack are a sinusoidal (wavy) crack path along the pipe, and “hackle” marks along the pipe crack surface that indicate the direction of the crack. At times, the crack will bifurcate (split) into two directions as it travels along the pipe.

The study of mechanism of crack propagation under pressure fluctuations has been done by Mengshan Yu, Weixing Chen, Richard Kania, Greg Van Boven, and Jenny Been. From this study, they conclude:

Where Variable amplitude (VA) cyclic loadings, which are close to the actual pressure fluctuations, are studied in current investigation, since the growth rate may be very different from that under. Constant amplitude (CA): even the cycles whose crack propagation driving force is below the determined CA threshold could still cause significant crack growth. However, such minor cycles are usually ignored in the study of nearneutral pH stress corrosion cracking (NNpHSCC) of pipeline steel ever since NNpHSCC was identified, although they are the major part of actual pressure fluctuations.

--

Source:

http://pgjonline.com/2009/03/20/rapid-crack-propagation-increasingly-important-in-gas-applications-a-status-report/

http://www.cme.engineering.ualberta.ca/en/NewsEvents/CMENews/2014/February/~/media/cme/NewsEvents/Documents/Poster-Mengshan.pdf