AbstractThe importance of real‐fluid behavior during the rapid decompression of dense natural gas mixtures has been investigated using existing one‐dimensional models for real‐fluid isentropic decompression (RID) and perfect‐gas isentropic decompression (PID). The results show that the assumption of perfect‐gas behavior may result in significant errors. In the case of ductile fracture propagation (DFP) analyses, the fracture‐tip pressure level may be underestimated by more than 20 percent.A real‐fluid nonisentropic decompression (RND) model has been developed in order to investigate the importance of nonisentropic effects in DFP problems. The results indicate that nonisentropic effects may be neglected for pipe sizes above approximate