A question regarding welding 'slightly' dissimilar metals

[copperkid3]

Does anyone have experience in knowing whether you can weld (and join together)

rolled carbon steel such as that found in a 500 gallon propane (LPG) tank and the

type of food-grade stainless steel found in a bulk milk tank? Special welding rod or

equipment needed to make it happen or too much trouble because of the difference

in thickness and gauge?

[haley1]

Before I answer I have to know/ how strong do you need it?

[copperkid3]

Originally Posted by haley1

Before I answer I have to know/ how strong do you need it?

* * * * * * * *
The 'plan' is to hopefully produce an outdoor wood-burning boiler system

that is better than anything that can be purchased commercially. Technically,

the term boiler is incorrect, as the heated water should never go to steam, but

would have safeguards of 2 separate t & p relief valves, (as well as 2 expansion tanks

along the output water line) but there would likely be some pressure that the stainless

would have to contend with as it would be the waterjacket, while the propane tank

would be the firebox. There would be several points and joints where the 2 metals

would have to be welded together to prevent water leaking into the firebox. Can this

be done successfully . . . .or not?

[calfisher]

Yep! Use stainless rod and it will mix just fine. Can be welded with stick or Tig.

[Ross]

So you're makign a pressurized water heater not an open system? Most commercial boilers are open and do not need T+P valves etc An expansion/rauto refill tank would be a bonus!

[Bob Huntress]

Copperkid, it can be welded, and better with TIG, yet the joint will be the point of serious corrosion. Is it possible to weld a flange surfaces and bolt them togather with a gasket seperating the two metals? Steel and stainless aren't the worst metals, but, I keep thinking of the same examply of the two welded together with corrosion eaten so much of the bead.

[CIW]

You can preheat your steel just a little, then use 308 stainless rod in a MIG. It will adhere well to both types of metals. If you are welding a pipe to one of your pieces get a threaded coupler of like steel or stainless, as the case may be. weld the fitting to the tank and then convert to a dialectric union.

[Joel_BC]

While we're on the subject, what about welding mild steel to the kind of carbon steel often used as tool material ("tool steel")? Which type of rod? Any particular corrosion or strength issues?

(Apology if this is diverting the intent of the OP in this thread.)

[ace admirer]

Originally Posted by Joel_BC

While we're on the subject, what about welding mild steel to the kind of carbon steel often used as tool material ("tool steel")? Which type of rod? Any particular corrosion or strength issues?

(Apology if this is diverting the intent of the OP in this thread.)

thats a different bird, 'tool steel" cannot be welded, if so it basically cannot be called a "tool steel" afterwards. its temper is "drawn". tool steel is very open term. not a perticular compound. Think low temperature "soldering" silver and such to bond it to softer shanks

[Goat Servant]

The only thing I can add is that working with stainless the fumes are going to make you sicker than a dog. PLENTY ventilation!!!!

[oneokie]

I welded some 14 ga. mild steel together with stainless rod in 1973. It has been in the weather since then and the joints are as good as the day it was welded.

[Joel_BC]

Originally Posted by ace admirer

thats a different bird, 'tool steel" cannot be welded, if so it basically cannot be called a "tool steel" afterwards. its temper is "drawn". tool steel is very open term. not a perticular compound. Think low temperature "soldering" silver and such to bond it to softer shanks

I understand the part about the temper going out of the piece, due to the heat involved when welding. But the composition of the metal remains the same, right? What I'm wondering about is - say you want to weld a carbon-steel bolt to a mild-steel component. I don't know if the bolt would have had any temper... so maybe I should not have used the term "tool steel". But is there any problem, in terms of strength, to weld the carbon-steel bolt to the mild steel? And what sort of rod would be best for doing it?

[ace admirer]

"carbon steel" is another loose term like tool steel. my experience, mind you,,,,is no problem, the carbon percentage is so low... i'd probably stay away from the deep penetrating rods like the 13 serieis....go for the 24 series like 7024, 11024 etc. i would not cool rapidly...let air cool


let me warn you,,,,i'm a hack,,,,,there are some expert welders at this site

[BjnMe98]

Some of the production boilers that use SS have had leaking issues.

I built my boiler out of a 500 gallon fuel tank and a 120 gallon propane tank.

http://www.owbinfo.com/viewtopic.php?f=6&t=370

[GSHamm]

Testing uploading a picture file to this post... FYI, a JPEG file can not be any larger than 700 x 700 pixels...

[Gianni]

Originally Posted by Goat Servant

The only thing I can add is that working with stainless the fumes are going to make you sicker than a dog. PLENTY ventilation!!!!

I believe that you are thinking of galvanized, not stainless.

[ace admirer]

i think the chrome and nickel sometmes in stainless causes problems too,,,,i think it causes your babies to be born with no clothes on.....

[wannabechef]

I agree, nickel stainless rod will do just fine on just about any steel...it's expensive though! I use it for armoring the trim edges of my commercial mowers every season.

[justin_time]

I pretty much just use stainless rod, even with mild steel. I did something similar to what you are talkng about, not a boiler as such, but a stainless steel hot water tank heated by my fireplace (as I only heat with wood) , you should have no problem with the welds as such, but any time you have dissimillar metals electrolitc corrosion can develop, I dont really understand it myself but after my system was in service for a few years, a couple threaded galvanized fitting rotted threw emptying 70 gallon of hot water all over the floor, I learned my lesson, and spent the extra to buy stainless steel fittings for the repair. So my advice is that mixing copper and stainless in the water system should be fine but if mild steel or iron is present electrolitic corosion can develop, so to counter that make sure the mild steel or iron are real thick as these are the metals that will be attacked over time, or so I found, Good luck

[reubenT]

If the water is being exchanged through the tank, that is, entering from a cold source and being used hot. It will have excess oxygen in it and cause any steel exposed to it to rust, and eventually rust through. All stainless would be best. If it's a recirculating system like for heating a house, a water treatment can be added to prevent rust, and it would then work fine long term with a regular steel tank. It would be safe to combine systems, have an open top wood fired water heater for heating a building, with stainless or copper coils inside to run the potable water through for heating the household supply water, that way the closed system will have the in between control of the open top tank so the close system never exceeds 212 F Any time you combine wood fire and water in a tank to get hot water, do it with an open top system, 0 pressure, a pipe of decent size from top of tank vented to atmosphere. Always! A closed system gets dangerous real fast, deadly dangerous! because a wood fire cannot be closely controlled with a thermostat like a gas flame or electric element. running a pressure vessel is not worth messing with unless yer going to have the right technology installed to run a steam power plant, (which is one of the things I am working on now) has to have many safety features and more than one pressure relief device. Look up some accounts of exploding water heaters. They've been known to blow buildings up like a bomb, or shoot out the roof like a rocket, ripping through walls and roof like they weren't there. video of test demonstration https://www.youtube.com/watch?v=jbreKn4PoAc

I've obtained a product called "boiler saver" it adjusts the PH of the water and eliminates oxygen for boiler service in steel tanks to prevent rust and corrosion. I'm pretty sure it would work in an open hot water system, but would have to ask Jim Conte to be sure. (he's the man who sells it in small containers and is a boiler professional)