Volume 3, Issue 9 (October 2006)
Proactive Mitigation of PCTFE-Related Ignition Hazards in Oxygen Systems: I. Development of a Voluntary Consensus Standard Specification to Control Property Variation in Finished PCTFE Parts
Revelations of dimensional instability in polychlorotrifluoroethylene (PCTFE) semifinished articles and finished parts raised concerns that leaks or part failure could occur during service, leading to catastrophic component or system failure, especially in high-pressure gaseous oxygen systems where flow friction, flow resonance, or kindling chain ignition mechanisms are operative. These concerns culminated in the release of an internal NASA Kennedy Space Center Problem Advisory and a Government-Industry Data Exchange Program Problem Advisory on PCTFE. Release of the advisories coincided with a task group study examining the factors contributing to property variation in PCTFE. More specifically, the effect of resin grade, process route, annealing method, and machining on dimensional stability, molecular weight, and crystallinity was determined. To better control dimensional stability, for example, a Biot-Fourier method is described that allows calculation of the time needed for PCTFE parts of known geometry to reach thermal equilibrium during annealing. A voluntary consensus material specification was then implemented to control properties in finished PCTFE parts used in aerospace applications.