Buried Wet Return Line

Christian Egli

The galvanized pipe will offer better corrosion resistance on the outside. That's all.

On the inside, the galvanized zinc won't help one bit. The slight acidic nature of condensate will corrode the zinc quickly. It will turn to a white powder.

This powder in itself shouldn't hurt, we're not talking about a large quantity of zinc oxide, but it will probably contaminate the water a little. So, I would make sure to keep an eye on the boiler water and test it regularly. Let’s see if someone who supplies chemical treatments for boilers has a major objection.

The zinc coating gone I do not know if the pipe would corrode further any faster than a black iron pipe.

I understand you already have all the galvanized pipe you want. While you're at it, why not install two sets of returns in one dig. You'll have a spare for in 37 years from now. Hopefully, they won't both be leaking.

If you still have to purchase the pipe, copper is better at resisting on the inside but it resists poorly to concrete and basic materials such as lime. The ultimate choice is stainless steel, it will last for ever and ever and will not corrode at all. It's not even particularly expensive in view of all the labour.

Put lots of slope on your pipe so that it runs itself dry between uses, that will slow corrosion from the inside.

Indeed, lime is ideal to slow corrosion on iron and steel. Now, the zinc will turn all grey and become stinky in the presence of a basic element.

Can't seem to win, no? With iron lime is still a good idea. Paint all the underground parts with tar, that will help a lot too.

Did you consider insulating your returns?

Best regards.

RonA

Buried Wet Return Line

I am replacing a buried corroded wet return pipe (1.25" i.p.), the second such replacement in this 75 year old two pipe vapor system. I intended to use galvanized iron pipe as I have it available, although I have heard that black pipe has generally been used. Does anyone see a long-term problem using the galvanized pipe? It's pretty much being used in the same role as a drain pipe, hence the thought that it would be ok. I learned from Dan that the buried line should be surrounded by lime and I will do that to protect it over the long haul. Thanks for your help.

clammy

black pipe

I don't believe galv pipe would be the right thing to use even if it's laying around sooner or later the galv internally will surcome to the heating and cooling and start to migrate into the boiler and possible the lwco ,pressuretrol,vents and safety plus possible die electric reation from dis silmar metals.Iwould do it in either steel or copper you can get trouth drains and set you insulated wet returns into it and snap the cover on it or use wolv wood on the sides and fit a cover on it i would recommend if you putting it back in the slab to insulate it ,allow for expansion and fill under the pipe with gravel instead of dirt .I'll see if i have a photo of peace clammy

RonA

Well guys, the message is clearer. I will avoid the galvanized. One of the things that has bothered me about copper in an otherwise iron pipe system is galvanic action at the junction of the two dissimilar metals. Granted, I may not be around long enough to know if it became a problem and the connection on both sides is above ground so it can be dealt with easily, but I think at this point it's the black pipe that wins. I will put an insulating coating on. Putting in two parallel lines is an interesting thought and would save the next guy a lot of trouble. I wonder, though, if the corrosion wouldn't happen anyway with or without the line loaded with condensate. Your thoughts on the iron-copper junction would be appreciated. Thanks for the help and illustration.

Steamhead (in transit)

If the iron-copper junction bugs you

use standard dielectric unions. I have never had a problem in this area though. Of course, Baltimore's water is pretty good.....

tim smith

copper to iron

use black couplings with 6" long brass nipples then copper female adapters. This helps bridge the dissimilar gap.