Sulphur prilling unit belt stress corrosion cracking

http://www3.interscience.wiley.com/cgi-bin/summary/102528975/SUMMARY?CRETRY=1&SRETRY=0

http://books.google.com/books?id=0XQBmsD8aIQC&pg=PA117&lpg=PA117&dq=sulfidation+of+316+stainless&source=web&ots=6BTFJlxrR2&sig=qcmOcBIJ0fDmNYxBAl6q0ybmxQs&hl=en&sa=X&oi=book_result&resnum=6&ct=result

What is the temperature of the prill on the belt max and average?

milo

Max temperature seen by belt is 120 C. Average temperature would be close to 60 C.

Raj

What are the chances you can upgrade to a duplex stainless steel option - such as 2205?

Or possibly going with a 6% molybdenum stainless such as 254 SMO, or AL-6XN?

Duplex Stainless Information

AL-6XN Datasheet

We are presently evaluating the possibility. Do you have any information on manufacturers who can supply duplex belts. Sanvik can supply but they limit the width to 1200 mm. Our belt is 1500 mm wide.

Raj

Could the dust be collecting the salt and causing your problems ?

http://74.6.239.67/search/cache?ei=UTF-8&p=Sulphur+prilling+unit+steel+belt&y=Search&fr=yfp-t-501&u=cms.efma.org/EPUB/easnet.dll/GetDoc%3FAPPL%3D1%26DAT_IM%3D000F7A%26DWNLD%3Dbooklet5.pdf&w=sulphur+prilling+unit+steel+belt&d=bl648fReRf-y&icp=1&.intl=us

www.arcmelt.com

These guys have just posted five technical papers explaining various corrosion protection coatings. I have there coatings in a few of my boilers right now. I know of a few of my refinery Buddy's looking into this for the exact same reason. I herd that this company is working with ORNL on metal dusting problems too.

Good Luck!

Guys,

thanks for all the inputs. A question, generally the corrosion is taking place from sea salts, this is more severe when the belt is not in use. There has been a suggestion that we can passivate the belt with weak Nitric acid when the belt is not in use for a long time. What are your comments. To me it looks like a workable solution.

Regards,

Raj

Why not do it the tried and effective old fashioned way. If not in use take it off, submerge in light machine oil and check periodically?

Raj

Stainless Steel type 316 is very sensitive to SCC in marine environments. The likelihood of SCC is a function of several factors like: internal/external stress of the components, chloride concentrations and temperature. Usually, a safe limit for 316 in terms of temperature to avoid SCC is 60°C and for Duplex approx 100 °C even if at a lower temperature, 80°C there have been some cases of SCC on duplex.

this is due to the fact that thermal cycle 'cause deposit and concentration of chloride with increasing likelihood of SCC even at low temperature (lower than 60°C). The only way to avoid this SCC is to use, as someone else said, higher alloyed material, like 6Mo SS or, if it's possible to paint the material but his mean maintenance activity to re-paint.

there is also a software for SS evaluation for external atmospheric exposure

hope this help

S

Yes and no. The protection of the alloy comes from a protective chrome oxide film that forms in the presence of oxygen. Passivation as we know it, for parts, would need to be chemically cleaned as to remove any surface contaminates and oxides (in your case chlorides). After this, you would oxidize the surface using a week acid in order to produce a very uniform and un-interrupted surface oxide. I suspect that in your case the addition of the Nitric would only worsen your cause. The best remedy would be to remove the chlorides from the surface by washing and adding to the surface via a solution of a week mixture of lime and water. We have had some success using this during shutdowns. If your process sees an environmental cycle (thermal cycle) then I would suspect that the cycle would be your primary cause of the cracking. The cracking is coming from the constant forming and removing of those surface oxides, thereby depleting the alloy of its chemistry.