In our NHT unit, tube material of stripper Column Overhead air cooler is SA-179 which is low carbon steel. So, if we use type SS 321 instead of SA-179 then will it be more sustainable in the wet H2S and wet HCl environment?
Answers
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18/03/2017
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Muhammad Faisal, OQ integrated energy company (Oman), engr.faisalfraz@gmail.com
I support that corrosion study to be conducted in order to find the reason for CS tube failures. without upgrading the material of construction followings checks to be carried out:
(Online solutions:):
(1). check the quality of Circulating sour water as reflux to fin fan (IF Any). if it has more NH3/Cl2 then it will stick to AFC tubes and can cause failure. (2). check OVHD Operating Temp>dew point Temp. (3). if there is a fresh demin water (low chloride water) injection facility Upstream of AFC, then make plan for schedule washing of finfan tubes with H2O extended hours to remove any deposition.
Permanent solutions:
(1). either change material from CS to Hastelloy or super duplux rather than going to SS321.
(2). If this is expansive, then get inspection report, up to how much deep inside the finfan tubes, they observe corrosion i.e. typically 1~2m is expected corrosion, so this is so then you may try Ferrul inserts (C-276 Hastelloy) (up to that height I. e up to middle of the incoming tubes. This will give more protection.
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16/03/2017
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I am not a metallurgist, but I do know that, as Mr. Rodwell has pointed out, any 300 series S.S. with chlorides presence will experience stress corrosion cracking. 400 series or higher alloys are being used. Duplex alloys have become popular.
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15/03/2017
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Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
While SS321 will be resistant to wet H2S, like other austentic stainless steels, chlorides (and HCl) are extremely detrimental. Additional wash water to reduce concentrations would be preferred to a stainless steel. If that is not feasible, a duplex stainless (2205) or nickel alloy (Inconel 600 or 800 series) would be preferred if the concentrations are significant and you see significant corrosion in carbon steel. You really need a metallurgist to review the data.
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