A number of ammonia cylinders burst during open storage in a field in
the month of June. The cause of failure was studied. No flaws in the c
ylinder material were detected. Under normal conditions, the tangentia
l stress (5.4 kg/mm(2)) in the cylinder is well below the yield streng
th (49 kg/mm(2)). The tangential stress increases with the rise of tem
perature of the ammonia. As long as some vapor exists inside the cylin
der, the liquid remains in equilibrium with the vapor, the cylinder pr
essure is equal to the vapor pressure of ammonia at that temperature,
and the rise in tangential stress is insignificant (0.14 kg/mm(2)/degr
ees C). However, as the temperature increases, the specific volume of
the liquid ammonia inside the cylinder also increases. The cylinder is
completely filled with liquid under certain conditions in accordance
with the bulk thermal expansion of the liquid; under these conditions,
the cylinder pressure rises sharply with increased temperature, causi
ng a large rise in tangential stress (4.76 kg/mm(2)/degrees C). Thus,
an approximate 10 degrees C temperature rise in a cylinder filled with
liquid ammonia can lead to failure.