CHEMICAL ENGINEERING TRANSACTIONS VOL. 31, 2013 A publication of The Italian Association of Chemical Engineering Online at: www.aidic.it/cet Guest Editors: Eddy De Rademaeker, Bruno Fabiano, Simberto Senni Buratti Copyright © 2013, AIDIC Servizi S.r.l., ISBN 978-88-95608-22-8; ISSN 1974-9791 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 Hans-Peter Schildberg *a , Giuseppe Sudano a , Christian Streuber b a BASF SE, Department GCP/RS - L511, D-67056 Ludwigshafen, Germany b Hochschule RheinMain, Fachbereich Ingenieurwissenschaften, Am Brückenweg 26, D-65428 Rüsselsheim, Germany hans-peter.schildberg@basf.com 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 C 2 H 4 /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 C 2 H 4 /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 C 2 H 4 /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 C 2 H 4 /O 2 /N 2 -mixtures with O 2 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 O 2 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). 1. Fundamental problems in establishing design rules for detonation pressure proof pipes When investigating the pressure/time/space profiles associated with gas phase detonations in pipes it is necessary to distinguish between long and short pipes (Figure 1). In each pipe type four different pressure load scenarios may occur (Figure 2). The pressure profiles in long pipes are theoretically fairly well understood in the region of the stable detonation (scenario 3) and for the reflection of a stable detonation (scenario 4) at a blinded pipe end. In both cases the pressure profiles are also amenable to experimental determination. A reliable theoretical prediction of the pressure profiles at the DDT in long pipes (scenario 1) and at the DDT in short pipes (scenario 5) is currently problematic. Additionally, the experimental validation of theoretical predictions is extremely difficult due to (a) the locations of the finite number of pressure sensors which can be mounted in a pipe only rarely coinciding with the location of the DDT and that (b) even with piezoelectric pressure sensors reliable quantitative measurements of very short duration detonative pressure peaks (full width at half maximum less than 30 μs for peaks at the DDT) are hard to achieve. 613