The Effects Of Sulfate Reducing Bacteria And Polarization Potential On The Stress Corrosion Cracking Sensitivity Of 16Mn And API X56 Steel In Sea-mud

The facilities under sea environment for a long time had corrosion danger. If they were not protected well, once stress corrosion cracking (SCC) occurred, serious losses would be caused. The sea-mud zone environment is very important, because the pipelines, the stakes of oil plat, etc. were all in the zone. In the sea-mud zone, sulfate reducing bacteria (SRB) are very active, and in order to prevent corrosion, almost all of the marine facilities are in the state of cathodic protection. At the cathodic potential, hydrogen would permeate steadily into the marine steels all the time. So in order to take measures to prevent SCC, it is very necessary to study the effect of active SRB in the sea-mud and the polarization potential on the hydrogen permeation of the marine steels, and make clear of the relationship between the hydrogen permeation and the SCC sensitivity.In this text, slow stress rate test (SSRT), electrochemistry impedance spectrum (EIS) technique, dynamic potential polarization curve and hydrogen permeation experiments were used to investigate the effect of active SRB in the sea-mud and the polarization potential on the SCC sensitivity of the marine steels.SRB were concentrated successfully from the sea-mud of Bo Hai, and the growth curve of SRB in the sea-mud was obtained. Experimental results showed that the quantity of active SRB were relevant to the main corrosion environmental factors of the sea-mud, such as E (S), E (Ag), pH, the open circuit potential and the conductivity and so on.The results of SSRT indicated that the cathodic potential added to the specimens and the existence of active SRB in the sea-mud could cause the brittle characteristics of the cracking more obvious and increase the sensitivity of SCC.The existence of active SRB in the sea-mud could affect the EIS of the marine steels. SRB could accelerate the cathode depolarization and increase the dissolution of the anode, which could accelerate the corrosion of the metals.The hydrogen permeation of the marine steels in the sea-mud could be accelerated respectively by active SRB and the cathodic potential added to the specimens. With the existence of active SRB in the sea-mud, the hydrogen permeation of the marine steels could also be accelerated by the cathodic potential.Finally this paper summarized: the existence of active SRB in the sea-mud and the cathodic potential added to the specimens could increase the hydrogen permeation and the SCC sensitivity of the marine steels.