Another dissimilar metal corrosion question

[DaveBP]

I have the opportunity to use a very large bronze wye strainer in my return line to the Tarm boiler. The pipes are 1-1/4" black iron. I also have some 1-1/4"
316 stainless steel ball valves (Ebay again) that I would like to use to close off both ends of the strainer to clean it out. This will require using reducer fittings between the strainer body and the valves. Stainless or bronze/brass fittings this size would cost more than the strainer and valves cost me. My affordable option is to use black iron hex bushings.

So my question for those of you out there that have seen everything and had to fix it.... is going from bronze to black iron to 316 stainless back to a predominantly black iron system asking for trouble?

 

[ewdudley]

I have the opportunity to use a very large bronze wye strainer in my return line to the Tarm boiler. The pipes are 1-1/4" black iron. I also have some 1-1/4" 316 stainless steel ball valves (Ebay again) that I would like to use to close off both ends of the strainer to clean it out. This will require using reducer fittings between the strainer body and the valves. Stainless or bronze/brass fittings this size would cost more than the strainer and valves cost me. My affordable option is to use black iron hex bushings.

So my question for those of you out there that have seen everything and had to fix it.... is going from bronze to black iron to 316 stainless back to a predominantly black iron system asking for trouble?

I don't think you need to answer the question. Since presumably it's on the return side I wouldn't hesitate to use CPVC bushings.

--ewd

 

[leaddog]

I have the opportunity to use a very large bronze wye strainer in my return line to the Tarm boiler. The pipes are 1-1/4" black iron. I also have some 1-1/4" 316 stainless steel ball valves (Ebay again) that I would like to use to close off both ends of the strainer to clean it out. This will require using reducer fittings between the strainer body and the valves. Stainless or bronze/brass fittings this size would cost more than the strainer and valves cost me. My affordable option is to use black iron hex bushings.

So my question for those of you out there that have seen everything and had to fix it.... is going from bronze to black iron to 316 stainless back to a predominantly black iron system asking for trouble?

I don't think you need to answer the question. Since presumably it's on the return side I wouldn't hesitate to use CPVC bushings.

--ewd

return side or not I would NEVER use cpvc in a boiler system again. 200* water does strange things. It can swell, get brittle, and I;ve seen 3/4in go to over 6in burried in sand with the walls about 10thousands thick. And then it DOES make a very large mess just when you need the heat.
There are charts out there but I don't think you will have a problem using black pipe
leaddog

 

[ewdudley]

...

I don't think you need to answer the question. Since presumably it's on the return side I wouldn't hesitate to use CPVC bushings.

--ewd

return side or not I would NEVER use cpvc in a boiler system again. 200* water does strange things. It can swell, get brittle, and I;ve seen 3/4in go to over 6in burried in sand with the walls about 10thousands thick. And then it DOES make a very large mess just when you need the heat.
There are charts out there but I don't think you will have a problem using black pipe
leaddog

Dave's not talking 200F water, nor IS he asking about pipe. It's reducing bushings he's after ON the return side OF a boiler system.

In my experience a CPVC reducing BUSHING constrained concentrically ON both sides by metal fittings won't go anywhere; nor will IT turn INTO marshmallow this side of 230F. It will certainly GET brittle, but so what?

--ewd

 

[heaterman]

Black iron is fine. Bronze and Stainless are both inert. If you were talking copper piping that would be a different matter. CPVC............mmmm......that's something I would never do. Code won't even permit CPVC to be used for the overflow line from a relief valve.

 

[ewdudley]

Black iron is fine. Bronze and Stainless are both inert. If you were talking copper piping that would be a different matter. CPVC............mmmm......that's something I would never do. Code won't even permit CPVC to be used for the overflow line from a relief valve.

As you please. However:

CPVC systems conforming to ASTM D2846 are rated for continuous service at 80 psi and 200 degrees F and are marked accordingly. The model codes recognize CPVC's capability to handle short-term pressure/temperature excursions well beyond these levels. Therefore, CPVC is well suited for usage as T/P relief valve discharge lines, evidenced by its faultless service history over the past two decades in this application.

Again, all hell would have to break loose before a CPVC reducing bushing between two metal fittings could possibly fail on the return side of a boiler.

--ewd

 

[heaterman]

Black iron is fine. Bronze and Stainless are both inert. If you were talking copper piping that would be a different matter. CPVC............mmmm......that's something I would never do. Code won't even permit CPVC to be used for the overflow line from a relief valve.

As you please. However:

CPVC systems conforming to ASTM D2846 are rated for continuous service at 80 psi and 200 degrees F and are marked accordingly. The model codes recognize CPVC's capability to handle short-term pressure/temperature excursions well beyond these levels. Therefore, CPVC is well suited for usage as T/P relief valve discharge lines, evidenced by its faultless service history over the past two decades in this application.

Again, all hell would have to break loose before a CPVC reducing bushing between two metal fittings could possibly fail on the return side of a boiler.

--ewd

Evidently that is a section of the code my State boiler inspector (who I have great respect for) was unfamiliar with when he failed to pass one of our boiler jobs due to using CPVC on the boiler relief valve. A T&P valve used on domestic plumbing may be viewed as a different use category than boiler work. Who knows?

 

[benjamin]

I see copper threaded to black pipe all the time in old boiler systems, and I haven't seen any problems. There was even a system out there that used 1/2 tinned steel tube with regular copper fittings and copper fin tube baseboards. Of course if you get oxygen in there that will be one of the first places to corrode, but hey that's what the shut offs are for right?