Quantification of the Static Equivalent Pressure of Gas Phase Detonations in Pipes at the DDT, in the Region of Stable Detonation (if any) and at the Reflection Point

Abstract

In order to establish guidelines for detonation pressure proof pipe design, experiments in 48.3x2.6 and 114.3x3.6 pipes (outer diameter [mm] x wall thickness [mm]) were conducted, in which deflagrative explosions of stoichiometric C₂H₄/air-mixtures at 20 °C underwent the transition to detonation. Initial pressures were chosen high enough to produce detonation pressures that caused significant bulging of the pipe walls. Hydraulic tests were carried through with all pipe material charges to determine the diameter increase as function of internal pressure. These results were compared to the diameter increase produced by the detonation experiments, enabling to assign static equivalent pressures (p_stat) to the detonations in the C₂H₄/air mixtures. P_stat can be regarded as the effective pressure “seen” by the pipe when exposed to the highly dynamic load. When, under application of the conventional (i.e. developed for coping with static loads) pressure vessel guidelines, the pipe is designed for this static equivalent pressure, it will withstand the detonative pressure pulse.
For gas phase detonations in pipes 8 different pressure scenarios can be distinguished. All scenarios were realized experimentally with stoichiometric C₂H₄/air-mixtures at 20 °C and for each one p_stat was determined. This includes also the worst case detonation pressure scenario, in which the DDT occurs within approximately one pipe diameter of the blinded pipe end.
When switching to stoichiometric C₂H₄/O₂/N₂-mixtures with O₂ concentrations between 21 vol.-% and 30 vol.-% the ratio between p_stat at the DDT and p_stat for the stable detonation decreases with increasing O₂ content. Whereas the ratio between p_stat at the reflection of the stable detonation and p_stat of the stable detonation will remain constant at about 2.49 for all detonative gas mixtures, the ratio between p_stat at the DDT and p_stat of the stable detonation must be expected to be strongly influenced by the reactivity of the gas mixture (increasing the reactivity will reduce the ratio).