A REEXAMINATION OF PROPANE TANK TUB POCKETS INCLUDING FIELD TRIAL RESULTS

When a rank containing a pressure-liquefied gas fails, one mode of fai lure involves the rank being propelled large distances by the released two-phase material. This mode of failure is called a tub rocket ann i t can pose a severe hazard to the public because of its unpredictabili ty. Field tests were recently conducted to study the effect of explosi ve devices on propane tanks. The tests included tanks of various sizes up to 2000 L (500 gal), In most cases, the rests resulted in puncture d tanks with transient two-phase jet releases. In some cases, the jet releases were sufficient to propel the tanks over considerable distanc es. In a small number of tests involving 470-L tanks, the explosive de vice resulted in the clean removal of a tank end, and this resulted in near-ideal launches of tub rockets. In one case, the rocket was launc hed vertically, and in another, the rocket was launched near 45 deg el evation angle giving a tub range of 370 m. In other cases, the explosi ve devices resulted in punctures, and in some of these, the resulting two-phase jet propelled the tanks over considerable distance. These ex amples gave a good opportunity to re-examine tub rocket models for tan ks containing liquefied gases. This paper describes a theoretical mode l involving two-phase critical flow propulsion of cylindrical tanks. T hree different critical flow models are compared, including the homoge neous equilibrium model (HEM), the homogeneous frozen model (HFM), and the Henry-Fauske model (HFK). Range predictions are compared with exi sting data and a model previously developed Mode I predictions are cal ibrated to the field trial results described in the foregoing and then used to predict realistic ranges for various sies of storage and tran sport tanks.