Abstract
Corrosion tests of mild steel and welded mild steel have been coducted to study the corrosion protection effect in the simulated inert gas environment of crude oil tankers. Morever, causes of corrosion cracking failures in inert gas environment of brass tubes for heating heavy crude oil have been invesigated. The results are as follows:
(1) The corrosion protection effects of mild steel in N2 gas containing O2 become 47% under O2/N2=0.1, 74% under O2/N2=0.04, 88% under O2/N2=0.01. The corrosion protection effect of 74% at O2/N2=0.04 shows that O2 concentration is not a corrosion factor.
(2) The corrosion protection effect in inert gas environment of oil tanker becomes minus 13.5% to that in air.
(3) The reaction of HSO3-+5H++4e=S+3H2O which occurs in low pH H2SO3 solution accelerates corrosion of mild steels together with O2 and H+ as cathodic reaction.
(4) Since the inert gas environment containing 250ppm SO2 causes the same corrosion rate as that in air, SO2 gas effects severely corrosion in the actual environment. Accordingly, control of SO2 gas is important for corrosion protection under inert gas system in oil tanks and ballast tanks.
(5) Corrosion failures of brass tubes for heating crude oil seem to be caused due to sulfide stress corrosion cracking and sulfide corrosion fatigue.
