Ignition Testing of Hollow Vessels Pressurized with Gaseous Oxygen

Abstract

A new testing method has been developed to measure the ignition resistance of metals and alloys used in pipe and pipe components for oxygen service. Hollow vessel samples, 80 mm in nominal diameter and I m long, are pressurized to 10 MPa with oxygen or oxygen-nitrogen mixtures. Ignition is started by the oxidation of finely divided iron powder, which is heated to combustion temperature with an electrical resistance wire. The quantity of iron powder necessary to burn a hole through the sample wall and the time elapsed between ignition and sample wall perforation are used as indicators of ignition resistance. The amount of metal burnt and its heat of combustion are taken as the measure of the extent of combustion. The metal compositions tested, ranked in a decreasing order of ignition resistance, are as follows: copper, cast brass, cuproaluminum, stainless steel, carbon steel, and Duralumin. Ignition is strongly dependent on oxygen concentration, initial temperature, and, to a lesser extent, pressure. Ignition resistance increases with wall thickness and is practically independent of the diameter of the hollow vessel.