Luis Antonio You have raised this question twice in 10 days time in the same forum. Answer is the same : Laminations and segregations /inclusions, have been detected after so many years of use of the tank. These were most probably in dormant state and will probably still remain dormant for another couple of years of use. Considering that the tank is in use for an atmospheric storage tank, H2S content in gasolene will not readily form linkages so easily. Even if formed ( for a notional fear due to understanding the mechanism of H2S and its effect on carbon steel with inclusions - assuming it is formed) the linkages will not propagate at a very rapid rate as to affect tank usage for gasolene storage. You should understand that the mechanism of H2S attack on steel is quite complex and different which requires higher partial pressure of ionic H2. This requires both higher residual stress and partial pressure of H2S. Both are unlikely for an atmospheric storage tank. Still, if you are worried about use of the affected plates in gasolene storage, provide additional re-inrocement plate (additions to thickness at weaker spots or spots with high variations in thickness (i.e, low thickness areas). This will solve your problem or fear to use in gasolene storage Trust this will help you C.V.Srinivasan Nishi Engineers Pvt Ltd India Dec 16,2006 E-mail: nishi@vsnl.com >I have a tank to storage gasoil with segregation and >laminations, mainly (It's a old tank). >I would like know what kind of attack can I have if product >storage inside has a hight % of H2S. Can I have steel H2S >attack and H ion migration to inside surface laminations and >creat H2 molecular ==> cracking tearing bettween inclusions >/ laminations? I mine linkage betwwen internal inclusions? >I will aprreciate a opinion. > >Thanks in advance. > >Luis

Luis Susceptibility to SSC increases with increasing H2S partial pressures a little bit above atmospheric pressure about 0.05 psi (0.0003 mpa) H2S in steels with a tensile strength above about 90 ksi or in steels with localized zones of weld or weld HAZ hardness above 237 HB. As Srinivasan pointed out H2S attack on steel is quite complex and different which requires higher partial pressure of ionic H2. This requires both higher residual stress and partial pressure of H2S. Both are unlikely for an atmospheric storage tank. I understand your preoccupation because you have to decide. If you feel uncomfortable with the situation, as also mention Srinivasan, you can reinforce the first shell plate following section 9 of API STANDARD 653 Tank Inspection, Repair, Alteration, and reconstruction API STANDARD 653. Don%E2%80™t worry Feliz Natal e Bom Ano Luis Marques