It is my understanding that galvanized steel is very susceptible to corrosion by sulfur acids produced by hydrogen sulfide and sulfur dioxide in the atmosphere. There may be a level of hydrogen sulfide which will not cause corrosion of galvanized steel in this case but I do not know what that level is. As with any corrosive agent, the corrosivity of hydrogen sulfide will depend upon concentration, temperature and what other species are present. It seems it would be less risky to use 316 stainless steel. There is a plethora of information regarding corrosion by hydrogen sulfide in text books that cover materials of construction and corrosion in the petroleum and petrochemical industries. I suggest you consult one of these references for more information.