Stainless Steel Pipe bearing on Carbon Steel Support
Stainless Steel Pipe bearing on Carbon Steel Support
(OP)
I have a 12" SCH. 10 Stainless Steel Pipe bearing on a carbon steel structural member. My question is this: Do I need some kind of wear pad between the two? I know I've heard something about this in the past, but I can't seem to remember what the rule is (nor can I find any literature on it). Additionally, If I were to guide this stainless steel pipe with a galvanized U-bolt, do I need a pad of some sort? Thanks in advance.





RE: Stainless Steel Pipe bearing on Carbon Steel Support
But look at it this way, your asking the question so somethign is tellign you its needed, the pipe is large diameter and thin wall, so it does not have alot of extra meat, and a 12" pipe filled with fluid, if that moves its a fair bit of frictional force to start eroding the pipe.
You might also want to consider the bi-metallic corrosion issue as well.
RE: Stainless Steel Pipe bearing on Carbon Steel Support
Thanks for the response. I'm not too concerned with the friction due to pipe movement (the contents are simply water at room temperature, so no impact loads are anticipated). The Bi-metallic corrosion is what I'm most concerned with. Is this something you can elaborate on a bit? Or point me in the direction of some decent literature that explains it? Thanks.
- Adam
RE: Stainless Steel Pipe bearing on Carbon Steel Support
RE: Stainless Steel Pipe bearing on Carbon Steel Support
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Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Stainless Steel Pipe bearing on Carbon Steel Support
rmw
RE: Stainless Steel Pipe bearing on Carbon Steel Support
You need a pad.
Depending on the environment, you might want to go farther and also prevent crevice corrosion with I-Rods and Nu-Bolts:
http://www.stoprust.com/i-rod-pipe-supports.htm
Mike Halloran
Pembroke Pines, FL, USA
RE: Stainless Steel Pipe bearing on Carbon Steel Support
maybe also these paper can be helpful:
http://www.hse.gov.uk/offshore/corrosion.pdf
http
S
Corrosion Prevention & Corrosion Control
RE: Stainless Steel Pipe bearing on Carbon Steel Support
Bi-metallic corrosion is a concern whenever you have two dissimilar metals in contact, by their nature one of the metals will be more prone to lsoe electrons and the other will be more prone to take them, thats whalf your corrosion circuit there, the rest of it will come from a medium to transfer the electrons.
Now on the external part of the pipe contacting the supports your not as likely to encounter a situation witha high rate of corrosion unless its very humid or the pipe and support will be getting wet frequently. as for how much corrosion there will be.... well im sure some will argue with me on this, but the bottom line about corrosion is you can only use rules of thumb, the science is there to calculate it out exactly, but no one has any way of knowing what the EXACT conditions are, or wants to take the time to do the calculations.
So all that being said i would suggest you put a wear pad betweent he pipe and support, like a PTFE material or some other inery material, ie a plastic not a metal.
But if your in a fairly dry environment and for some reason you want to avoid spending the few dollars on some wear pads i dont think you have to be overly concerned about corrosion, but here im just guessing as i dont know the environment.
RE: Stainless Steel Pipe bearing on Carbon Steel Support
RE: Stainless Steel Pipe bearing on Carbon Steel Support
If your ever curious about 2 metals setting up a corrosion cell a simple way to judge si to look up a Galvanic series, most of these tables will at the very least list the metals in order from active to passive, basically the further apart the metals are on the table the more corrosion there will be, and it is the more active metal that will corrode, the passive metal will wather the extra electrons.
RE: Stainless Steel Pipe bearing on Carbon Steel Support
RE: Stainless Steel Pipe bearing on Carbon Steel Support
So, a galvanised U-bolt will also need to be shielded from the stainless since the zinc will be removed at some point (accelerated by the galvanic effects discussed above). Generally, this is achieved with PTFE sheet. Some people use rubber but it ages and falls apart.
The above is also a reason why you will find specifications demanding strict segregation of work areas and tools in fabrication shops dealing with carbon and stainless steels. Even grinding dust can initiate pitting in stainless steel.
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Stainless Steel Pipe bearing on Carbon Steel Support