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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsGeneral Corrosi...General Corrosi...SCC of 304L in Amine serviceSCC of 304L in Amine service
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1/17/2010 9:00 AM
 
[updated:LAST EDITED ON Jan-17-10 AT 08:07 AM (CDT)]In our amine plant CO2 absorber we found fine cracks in the 304L tray supporting ring at its top section. Remaining areas of the absorber do not show any signs of such cracks. Does anyone have similar experience with SCC in 304L for amine service? There are two possibilities we are suspecting, one is caused by polythionic acid and the other due to chlorides (possibly caused by HSAS). Eventhough there are lot of failure cases in the bottom portion of CO2 absorber mainly due to SCC that I'm aware of, I've not heard many cases of SCC in 304L supporting ring at the top portion where normally the contaminants and the aggressive corrosive environment are less. steve
 
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1/27/2010 9:00 AM
 
Stevemc S.S 304 tray support ring plate / weld fine cracks (SCC) is not an ununsual problem encountered in CO2 absorber towers. HSAS due to alkaloamine degradation is a possible reason to induce SCC or due to chloride or alkali concentration at higher vapor (indirectly higher temperature at the top tray segments or at bubble cap tray segments in higher plant conditions) or possible air incursion during a shut down (inadvertent entry and SCC due to polythionic acid corrosion of S.S 304 in CO2 absorber) is also a possibility. You have mentioned that SCC at the bottom tray segment in CO2 absorber towers as known to you from case histories studied by you. One of the most common problem encountered by many users in CO2 absorber towers will be erosion -corrosion due to vapor / CO2 mixtures from bottom tray segment collapse and rasching ring collapse dumped at one side of the tower with gas-vapor mixture eroding the C.S shells. Occasionally, tray segment collapse would also contribute to SCC of S.S 304 tray plates or during a shut down with inadvertent air entry causing polythionic acid corrosion of tray segments /wedls. Please check the vapor load (during max. operating plant conditions) at the top tray segments in your CO2 absorber tower , check the velocity of gas-vapor mixture at the top tray segments, any possible degradation of amine to cause HSAS at the top tray segment (either due to amine used had degraded or re0circulated without top up during higher plant loa run conditions), operational control of temperature profile not monitored carefully at the top tray segments. In all probability, if the temperature profile in your plant had seen wide variations, possible chloride induced SCC at the higher hard zones in tray plates due to either alkali or chloride concentration build upat tray support rings could also be a problem or possible H2S-CO2 mixture development and inadvertent air entry during shut down without proper neutralization care of the absorber before opening man holes could also contribute for such failures in S.S 304 tray support ring plates. Finally, for your information, S.S 304 ring support cracks is not an unusual occurrence in amine treated CO2 absorber towers. Hope this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India E-mail: nishi@vsnl.com Jan 28, 2010 >In our amine plant CO2 absorber we found fine cracks in the >304L tray supporting ring at its top section. Remaining >areas of the absorber do >not show any signs of such cracks. Does anyone have similar >experience with SCC in 304L for amine service? There are >two possibilities we are suspecting, one is caused by >polythionic acid and the other due to chlorides (possibly >caused by HSAS). > >Eventhough there are lot of failure cases in the bottom >portion of CO2 absorber mainly due to SCC that I'm aware of, >I've not heard many cases of SCC in 304L supporting ring at >the top portion where normally the contaminants and the >aggressive corrosive environment are less. > >steve
 
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