Stainless steel vessel with carbon steel stiffener

[nstress]

Hi Experts

I have a pressure vessel made of stainless steel designed for vacuum (design temperature 200 deg.C). I need to have stiffeners; according to design carbon steel stiffener is sufficient. From the point of view of welding, is it advisable to use only stainless steel stiffener?
(I have used stainless steel vessel to avoid problems due to erosion of steam flow.

thanks for your help

 

[prex]

There are many vacuum vessels out there with carbon steel rings and solid SS wall: it's a quite common solution.
Of course you will need to protect the rings from corrosion, unless they are covered by the insulation.

prex

http://www.xcalcs.com

Online tools for structural design

 

[nstress]

Thanks, Prex

 

[DSB123]

nstress,
I hope you have considered the differential expansion between the CS and the SS at the elevated temperature of 200Deg C as this could give rise to high stresses around the welds. Also it is general to not directly weld CS directly to the pressure part of a SS pressure vessel but introduce a SS section between.

 

[arto]

One way to analyze this - Look in the old 3rd ed Roark Table XIII case 9.[like your belt's on too tight ;-) ] Get an equivalent pressure for the differential thermal expansion & calculate stresses. Also check the line load on the attaching welds. Watch out for stress corrosion cracking! [p.s. there's a couple more "threads" on this subject - search the eng-tip archives]

 

[arto]

Oh yeah - if you're insulating it, think about using insulation per ASTM C-795 "Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel" - low leachable chlorides.

 

[zekibk]

nstress,

Please do not forget to use SS 309 ( high nicel content)electrodes for welding, to prevent welding zone from ferritic and/or martenize type of stainless steel formation ( instead of austenic- I assume vessel is austenic stainless steel)

zeki

 

[deanc]

Review UG-30,make sure you have a qualified welding procedure for the disimilar material.

 

[bmoorthy]

If CS Stiffner is going to be welded to SS, then Use E 309 Electrode and make sure that supporting procedures are available.

To take care of differential expansion and corrosion problems of shell wall/welds, but still use CS stiffners, a small extra effort would generall do. First deposit SS 309 on CS ring then assemble the ring and then weld the ring to shell using SS 309 again.

 

[Davis224]

Why would you want to do this???

You have an entire vessel of stainless steel. What is your motivation for providing a carbon steel stiffener ring? To save money? How much will you save by choosing carbon steel over the same material, where expansion will not be a factor, where welding will not be different than for any other joint, where the obvious effects of corrosion will threaten the only design feature that keeps the vessel from collapse under vacuum??

Make it easy on your maintenance people and easy on your welders. Avoid unnecessary stresses on your vessel and make the stiffener ring of the same material.

 

[nstress]

Yes, I have decided to use stainless steel stiffener to avoid future problems.

Thanks to all of you