Steam Boiler Piping Dissimilar Metals

Billy_DeVincentis

Hello everyone,
I am new to this forum,
so glad I could find a place to get some advice.
Last summer I had seen water spots in the concrete above the wet returns for our steam boiler system. I had replaced the return lines around 20 years ago but I thought I would have gotten longer than that. In any event I cut out the floor and replaced all wet return piping from the headers all the way down to the boiler itself and also redid the hartford loop. One difference this time, I spent about $3000 and did it completely in Stainless Steel 316. Job came out very nice, I finished the piping just a couple of days ago, I am going to seal the underground pipes with a special asphalt sealer which I bought from Eaton chemical (9183). It is especially meant to protect buried piping. I assume that I will never again do return pipes on this house (hope not, Im 53, I can't picture myself doing this in my 70s LOL). One spot that I was a bit stumped on was the conversion points from cast iron to stainless steel. On the return lines by the headers, I used brass gate valves with cast iron going down from the header and stainless steel coming out on the other side of the valve. At the boiler, I replaced the 1-1/2" x 5" nipple at the front bottom of the boiler with a brass nipple and then continued on with Stainless Steel into the hartford loop. Above the hartford loop going to the main header I again used a brass nipple to go from stainless steel to cast iron. Was this necessary? Will I eventually get galvanic corrosion on the brass nipples? Was there a better way to do this?

acwagner

That's amazing on so many levels. Got any photos?

What was the failure mode of the wet return? Your soil conditions must be especially harsh for it fail in 20 years. Did you consider instead of direct burial building a concrete cavity for the pipe to sit in so it's not in direct contact with the soil?

As for the galvanic corrosion, stainless/carbon steel are closer than brass/steel on the Anodic index, so the brass was not necessary.

Between stainless steel and iron/carbon steel, the iron/steel will suffer the corrosion. Given the history of all this, I would use a regular black pipe nipple to connect into the boiler to act as a sacrificial piece. I would rather a pipe nipple corrode vs. the boiler vessel itself.

Billy_DeVincentis

Well
to be honest at this point it's finished and up and running. Unless there is a serious problem using brass nipples, I will leave it for now. I definitely have pictures.

Billy_DeVincentis