Stainless to Copper Pipe

well usually in sanitary-water systems going from carbon steel to cu-tubing is either via a ball-valve in between the transition, or coupling.

<...What do I need to do to join these two metals?...>

If there is a corrosion concern then 'galvanically isolate' them, so that there is no electrical continuity between the two metals other than through the fluid in question. That way, there won't be any tendency for corrosion. However, if the fluid is non-conductive, then just make the connection and don't worry about it.

Alternatively, run the whole line in one material. Clearly the fluid is compatible with either metal?

hmmm well it depends what hes running then. size availability can be one factor.

thanks everyone We have 3" npt male threaded copper and 3" npt female threaded stainless 304 the fluid running in the pipe is water does this setup work? or will we have reaction between the two materials Thanks again for your help

nothing to write home about.

I've used brass between many junctions, but I'd have a hard time justifying that in this set up.

No problem.

According to the Galvanic Compatibility Table The potential difference between SS and copper is .15V which is the maximum acceptable for harsh environments (salt water).

Normal pipe thread tape should suffice.

Silver solder is one way.

There are proprietary anti-corrosion substances available. Just Google what you want to do. Welding is another option. Have been welding cupronickel to stainless steel for few years now. A welding shop that specialises in marine work will know.

Cheers
S.

SLIP TO THREAD EACH METAL....PLASTIC UNION BETWEEN.....SOLVED

MR. GUY

You need to install a die-electric union they are made for this and commonly used.

pipewelder

If you can't get a die-electric union where you are located.(they are common at pipe supply outlets in the USA) Then you can install a short piece of PVC pipe between the copper and S/S to act as a current insulator.

pipewelder

The thread has progressed further and it now seems that you are running potable water through this pipework. If so, I'd agree with the previous comments in the line of' just thread the pipes and dope the thread with either tape or teflon filled liquid dope and screw 'em together. Both stainless and brass fittings are universally avilable and either are appropriate in this case, if you should need to add fittings to make the joint easier to do. No problems. Saltwater? Depends on the level of salinity. In the extreme case you may need to take advice on galvanic corrosion in the joint. But, if it aint broke, don't fix it.

There are a lot of copper brazed 304 stainless steel heat exchangers that are used for cooling water every day. So I agree with Techno, unless you are anticipating a very corrosive environment, you should not have a problem. I would think that pipe tap in between the threads should be more than adequate.

If you put a brass to copper fitting between the two you should be OK,OK?.

Due to the little difference in potential it should not be a problem. One recomendation in plumbing systems is :

"Copper can be connected to stainless steel provided it is via a compression or capillary union":

http://resource.npl.co.uk/docs/science_technology/materials/life_management_of_materials/publications/online_guides/pdf/avoidance_of_corrosion_in_plumbing.pdf

this is true if the two areas (anode and cathode) are of the same size. if the Area of the cathode (stainless steel) is gerater than the area of copper then corrosion of copper is possible.

"stainless steel and copper tubes can usually be joined without problems resulting, but accelerated corrosion of the copper tube is likely to occur if it is attached to a stainless steel tank"

http://resource.npl.co.uk/docs/science_technology/materials/life_management_of_materials/publications/online_guides/pdf/bimetallic.pdf

http://www.corrosionist.com/Corrosion_Type_Galvanic_Corrosion.htm - sorry, link no longer available

hope this helps

S.

corrosion control

you guys are eingineers!.. the longest answers to the simplest questions.

I agree 100% why would anyone not want to use a die-electric union that is made for this and has been used on plumbing for many years is beyond me. I am always trying to come up with different ways to "skin a cat" so to speak but in this case one should use the product that is made for the application I think.

pipewelder

So! Just screw the bastard together and don't worry about it. A bit of ribbon dope and you're done.

Cheers,

S.

Just a minuet, who you calling a dope? someone hold him down Ill marmalise him.

Bazzer