An oxygen tank with a volume of 2.5 ft3 is kept in a room at 50°F. An engineer has used the ideal gas equation of state to determine that if the tank is first evacuated and then charged with 35.3lbm of pure oxygen, its rated maximum allowable working pressure (MAWP) will be attained. Operation at pressures above this value is considered unsafe.

(a) What is the maximum allowable working pressure (psig) of the tank?

(b) You suspect that at the conditions of the fully charged tank, ideal gas behavior may not be a good assumption. Use the SRK equation of state to obtain a better estimate of the maximum mass of oxygen that may be charged into the tank. Did the ideal gas assumption lead to a conservative estimate (on the safe side) or a non conservative estimate of the amount of oxygen that could be charged?

(c) Suppose the tank is charged and ruptures before the amount of oxygen calculated in part (b) enters it. (It should have been able to withstand pressures up to four times the MAWP.) Think of at least five possible explanations for the failure of the tank below its rated pressure limit.