Experimental and theoretical studies were carried out to understand th
e effects of air leak through the snorkel of a RH degasser on desorpti
on and absorption of nitrogen in molten steel during vacuum treatment.
The pressure and gas composition in steel pipes inserted into the ref
ractory of up-and down-legs were examined. Snorkels were sealed with a
rgon gas and change of nitrogen content in steel were compared with co
nventional treatment without argon gas seal. The outer side pressure o
f the down-leg is higher than the inner side one, whereas the pressure
distribution of the up-leg is to the contrary. The main gas compositi
on in the down-leg is nitrogen and that of the up-leg is argon. These
mean that the air leak spot exists in the down-leg. Desorption and abs
orption rates of nitrogen are balanced at 20 ppm when snorkels are sea
led with argon gas, whereas balance content is 27 ppm for conventional
treatment without argon gas seal. The kinetic analysis on nitrogen be
havior made clear that the amount of nitrogen gas leak when argon gas
was used for sealing snorkels was reduced on the average by one half a
nd standard deviation of that value by one fifth compared with the con
ventional treatment. The relation between the rate constant for nitrog
en removal and nitrogen absorption rate by air leak was shown in order
to obtain the aimed final nitrogen content at the fixed treatment tim
e.