Pipe Supports - Material Issue
Pipe Supports - Material Issue
(OP)
I will be installing a horizontal section of 304H SS pipe in an outdoor, refinery environment. The plan is to weld a pipe shoe to the pipe and rest it on existing galvanized steel. However, I am concerned with galvanic corrosion.
What is the best approach?
1. Make the pipe shoe of 304H and rest it directly on the existing galvanized steel?
2. Make the pipe show out of another material that will not react with the galvanized steel? If so, this will require me to weld dissimilar metals together. If this is not a problem, do you have any suggestions on the material?
3. Proceed with 304H pipe shoe, but put some type of insulating material between the two metals.
4. Some other approach I have not thought of. Perhaps some of you have suggestions for this application.
Thanks in advance for taking the time to read and respond to this post.
Regards,
Charlie
What is the best approach?
1. Make the pipe shoe of 304H and rest it directly on the existing galvanized steel?
2. Make the pipe show out of another material that will not react with the galvanized steel? If so, this will require me to weld dissimilar metals together. If this is not a problem, do you have any suggestions on the material?
3. Proceed with 304H pipe shoe, but put some type of insulating material between the two metals.
4. Some other approach I have not thought of. Perhaps some of you have suggestions for this application.
Thanks in advance for taking the time to read and respond to this post.
Regards,
Charlie





RE: Pipe Supports - Material Issue
RE: Pipe Supports - Material Issue
The only concern will be the temperature you have to choose a sliding plate material, which withstands your temperature.
luis
RE: Pipe Supports - Material Issue
304SS is considered a cathode (noble metal)
Carbon/Gal Steel is considered an anode (active metal)
The relative area of each of the exposed metal surfaces is also a consideration. If the area of the cathode (304SS) is very large, and the anode (Gal)is very small, the current produced is likely to be very high and the anode will corrode quickly.
For example, consider a large stainless structure with carbon screws (in an electrolyte of course), the carbon screws will corrode, but a large carbon structure with stainless screws will corrode very little if any.
Hope this helps !
Nic
RE: Pipe Supports - Material Issue
RE: Pipe Supports - Material Issue
1) Dissimilar metals
2) Metal-to-metal contact
3) Metals in the same conduction solution (usually called an electrolyte)
If any of these elements is missing, galvanic corrosion cannot occur. So if there is no chance of an electrolyte, then no corrosion will occur.
RE: Pipe Supports - Material Issue
RE: Pipe Supports - Material Issue
RE: Pipe Supports - Material Issue
The concern is normally for pressure containing parts coming into contact with galvanized parts and not the pipe shoes sitting on galvanized steel.
I do have other comments though. Since you are using 304H grade stainless, I assume your pipe must be very hot, possibly 1000 - 1400 deg. F.
You need to take a close look at the temperature of your shoe where it contacts the galvanized steel. That temp. could easily exceed what the steel and or galvanizing can withstand.
If that's the case you can extend your shoe height or use pre-insulated pipe supports (Hot Shoes) such as Pipe Shields, mentioned above, now owned by Piping Technology & Products or High Temp Slide Plates. The PT&P website is http://www.pipingtech.com/ and you can see these products.
Good luck,
NozzleTwister
Houston, Texas
RE: Pipe Supports - Material Issue
RE: Pipe Supports - Material Issue
NozzleTwister and most recently rconner have hit the nail on the head with their input. The high temperature will melt the zinc coating around 775 deg F.
So, I managed to find a hot shoe that I think will suit our needs.
Thank you all very much.
Until next time....
Charlie
RE: Pipe Supports - Material Issue