April 2013 Pressurisation rates in the UN 2(b) & 8(c) Koenen Tests David L Kennedy and David Coutts Presented by Noel Hsu

Page 1 Topics Introduction Effect of Pressurisation Rate on Fragmentation Effect of Temperature on Steel Properties and Fragmentation Conclusions and Recommendations

Shock diamonds “Shock diamonds” are often observed whenever hot, high pressure gas expands at high velocity through an orifice or constriction, creating a series of shocks and rarefactions. The height of the first Mach disc is controlled by the pressure difference between internal gas reservoir and the external atmosphere. Under certain test conditions, the internal pressurisation rate in the Koenen Test can be deduced by observing changes in the height of the Mach disc. This requires high speed video at rates of at least 1,000 fps for ANE, and up to 50,000 fps for typical Class 1 materials.

Shock diamond in Koenen Test

Pressurisation rate experiments The relationship between internal pressurisation rate and tube fragmentation for a Ø2 mm orifice has been measured using a series of modified Koenen Tests. These tests used three double-base smokeless powders with different burning rates. The Koenen tubes and orifices were completely filled to ensure that deflagration ignited at the orifice and then burnt downwards. Each test was videoed at 28,800 fps, and the height of the resulting Mach disc tracked over the final 500 µs leading up to tube rupture. The internal pressurisation rates were determined, assuming the burst pressure of the Koenen tubes was 30 MPa. A series of numerical simulations was performed to examine the effect of pressurisation rate on burst pressures and fragmentation patterns. Alliant Power Pistol 39/174 Hand gun Winchester WXR 159/174 Rifle ADI AR /174 Rifle

Pressurisation rate experiment for PowerPistol (39/174) Page µs-69 µs-104 µs-130 µs-156 µs-182 µs+69 µs+35 µs0 µs (5.4 seconds) Rate: 28,800 fps Orifice: Ø2 mm Completely filled to ignite deflagration from orifice Test duration: 5.4 seconds Pressurisation Rate: 70 MPa/ms Test outcome: “G”

Page 6 Koenen Test Result

Pressurisation rate experiment for PowerPistol (39/174): The Movie Page 7 K148_PowerPistol_full_2mm.wmv

Conventional Koenen Test: PowerPistol (39/174) -35 µs-69 µs-104 µs 190 m/s +69 µs+35 µs0 µs (7.3 s) 300 m/s This test was conducted with the tube filled to the normal level 15 mm from the top. No venting was observed prior to the explosion at 7.3 s, so the pressurisation rate cannot be measured. It is likely that the deflagration was ignited at the base of the tube by heat from the lower burner. Note that multiple fractures were created simultaneously, leading to fine fragmentation and a “G” result. Test K140 Duration: 7.3 s Camera: 28,800 fps Orifice: Ø2 mm

Fragmentation versus Pressurisation rate Page 9 PowerPisto (39/174)l 70 MPa/ms AR2214 (159/174) 45 MPa/ms WX (170/174)R 40 MPa/ms Double-base smokeless powders Tube and orifice completely filled to ensure ignition at orifice Assume: WXR burst tube at pressure of 30 Mpa Decomposition gases from all 3 powders behave similarly

Numerical simulation of Fragmentation versus Pressurisation rate Page 10 If the strength of the steel tubes did not depend on temperature, a pressurisation rate of about 20 MPa/ms would be the dividing line between “Explosion” and “No explosion” in the Koenen Test. This animation starts 5 µs prior to the first rupture of each tube. uniform25_vs_rate.wmv

Page 11 Koenen Test Result

Yield strength of DC04 (MTC Manual) sheet steel

Burst pressure versus temperature for Koenen tubes (Using physical Property Data)

Non-uniform temperature distribution at longer times 0 s30 s60 s90 s120 s Discolouration

Effect of temperature at 100 MPa/ms This animation starts 5 µs prior to the first rupture of each tube. The assumed temperature distributions are shown at the start, followed by the dynamic velocity fields. All tubes develop sufficient independent splits to tear into numerous fragments. All would be classed as “G” type results. At this high pressurisation rate, the result is determined by the internal decomposition rate of the test substance, and not by the thermal properties of the steel tube. 100MPapms_effect_temperature_distribution.wmv

Effect of temperature at 10 MPa/ms This animation starts 5 µs prior to the first rupture of each tube. The assumed temperature distributions are shown at the start, followed by the dynamic velocity fields. The two cooler, stronger tubes in the top row tear open only enough to give a “D” result. The hotter, weaker tubes in the bottom row continue to tear themselves apart, giving what is now classed as an “F” type result. At this slow pressurisation rate, the result is determined by the thermal properties of the steel, and not by the internal decomposition rate of the test substance. 10MPapms_effect_temperature_distribution.wmv

Experimental ANE with Ø2 mm orifice Page 17 Rate: 28,800 fps Orifice: Ø2 mm Normal fill level Test duration: 134 seconds +174 µs+139 µs+104 µs+69 µs+35 µs 0 µs (134 s) +243 µs -35 µs-104 µs-347 µs-694 µs -2,778 µs Pressurisation Rate: 4 MPa/ms Test outcome: “F” If an event with this pressurisation rate had occurred after only a few seconds of heating, the cool, strong steel tube would have split open, but stopped at a “D”. After 134 seconds heating, the single split down the back has continued to tear the hot, weak tube into type “F”.

Experimental ANE with Ø2 mm orifice: The Movie Page 18 K151_ANE_V2P_2mm.wmv

Pressurisation rates for experimental ANE ANE35 (K152) 0 MPa/ms Duration: 112 s ANE05 (K137) 0 MPa/ms Duration: 71 s WXR (K147) 40 MPa/ms Duration: 5 s Slowest burning smokeless powder ANE35 (K155) 0 MPa/ms Duration: 101 s

Page 20 Conclusions At fast pressurisation rates, multiple cracks are initiated in the tube walls, and the tube tears into multiple fragments for an “F” or “G” type true “Explosion”. At slow pressurisation rates, only a single crack is initiated in the tube walls. If the tube is cool, the crack does not grow, and the tube splits open into a “D” type true “No explosion”. If the tube is hot from prolonged heating, the initial crack continues to grow and to bifurcate, tearing the tube into multiple fragments for an “F” type (though now false) “Explosion”. Should the criteria for the UN 8(c) Koenen Test for UN 3375 ANE include consideration of test duration to account for effects of prolonged heating? e.g. 60 seconds Alternatively, is a replacement test required that measures pressurisation rate directly, rather than indirectly via fragmentation? > 20 MPa/ms: “Positive” explosion < 20 MPa/ms: “Negative” no explosion Future planned work: Use an infra-red camera to determine dynamic temperature distribution throughout tube walls for various classes of materials. Examine effect on fragmentation pattern of employing only lowest burner in 8(c) Koenen test. Would removal of hotspots on side walls eliminate false “F” type “Explosions” at slow pressurisation rates? Use high speed video to observe the formation of shock diamonds in the UN 8(d) Vented Pipe Test in order to measure internal pressurisation rates.

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