SS Welding to Steel

First off, welcome Joe Reeves,

I take it your asking about welding between stainless and Carbon steel. I 'assume' you have some what experience in welding. With this in mind, you would use a 309 filler weld. If you need a more detailed answer, please give a more detailed question and information.

Or, search this site, it has been discussed quite heavily.

Joe,

The two steels don't care what you use to weld them, within reason. They are close enough in composition that, if kept dry, it won't matter.

I have welded ss to cs with cs wire and it is still in service, outside, in Arizona.

Now, before the purists (self proclaimed experts) flame me, there are real reasons why you should at least do as 911 says and use ss wire/rod.

Insurance liability is the biggest problem you have. Aside from the fact that "the roof collapsed", once already, personal injury is your biggest hurdle.

Why did the roof collapse in the first place?

Do you have the proper permits and engineering support for this?

The joists were old and the particular area has a high ammonia wear and tear on the structure over time .plus the fact loads of pipe and conduit attached to the joists along with six inches of rain in thirty minutes didn't help.just needed the particular rod I need to weld the two metals together. I take it the rods are good for the as bridging I will have to weld in also

It sounds like a disaster waiting to happen, again.

The filler metal is no stronger than the parent metal. Welding will only induce stresses that were not there before.

That's about all I can say.

Good luck.

If i were you, I'd find out why there is so much ammonia there and stop it, Mildred, then, I'm funny that way.

If the concentration of Ammonia is high enough to do all this corrosion damage to the steel beams, what is it doing to the lungs of the personnel that work in that area or nearby?

Inhalation is second only to injection for the fastest routes of entry into the body. Fro Ammonia the ACGIH has established a 8hr TWA of 25ppm and a 15 minute STEL of 35ppm. http://www.cdc.gov/niosh/pel88/7664-41.html http://www.cdc.gov/niosh/docs/81-123/pdfs/0028-rev.pdf OSHA has a 50ppm 8hr PEL https://www.osha.gov/dte/grant_materials/fy09/sh-19489-09/fs4-howmuch2.pdf

Before replacing any of the steel with stainless steel some engineering should be done to determine the source(s) of the ammonia and correct those points of emission before doing any steel work. If not for the sake of the steel, do it for the sake of the people's lungs. If this is a refrigeration system it is supposed to be a closed loop. If this is a manufacturing point or point of usage it should be a closed system with adequate vapor recovery.

Good Luck, Old Salt

As has been noted, 309L will be the best filler rod for most SS to CS applications.

Just be a bit careful of weld cracking due to SS having higher thermal expansion and lower thermal conductivity characteristics than Carbon steel.

The SS will likely be tightly constrained when welding, and will expand more and then contract more slowly than the CS. The CS will cool and shrink more rapidly and conduct heat away from the weld zone which can cause cracking of the weld as the CS shrinks back.

To reduce this possibility you can moderately preheat the area around the joint or apply moderate heat after welding to slow the cooling process. Note the word "moderate" keep the heat low to avoid upsetting the alloy mix of the SS near the weld.

You will need to thoroughly clean the old steel at the weld zone to prevent contamination, and preferably follow that with a wipe down of both metals at the areas to be joined with Acetone or similar to remove sulphur, phosphorous and other deposits which can contribute to cracking.

When welding stainless steel to carbon steel, always use rod of the composition of the stainless steel or a specified type stainless steel rod. 304 to CS use 304 rod, 316 to CS use 316 rod. Do not use CS rod with this mixed weld. Do not use things like 6010, 6011, 6012, 6013, 7014, 7018, etc. They will not hold, they are CS rods.

The same holds true for stainless to stainless of different compositions. 304 to 316, use 316 rod, etc

Good Luck, Old Salt

As previous stated by others, I'd be concerned about welding the dissimilar metals due to thermal issues. I'm assuming you are installing Open-Web Steel roof joists here, that conform to the Steel Joist Institute (SJI) standards?

Why can't you drive SS self-drilling screws through the roof joist baseplate into the beam top flange? I wouldn't go any less than 0.25-inch shanks. Keep aware that you may need to meet or exceed minimum horizontal shear loads due to wind loadings through diaphragm action of the roof construction, as determined by the P.E. if there is one involved on this project. You may have to install multiple fasteners to meet the horizontal shear load requirements. Warning: depending on the base steel thicknesses, you may have to pre-drill holes.

Or you can use RAMSET SS powder-activated pin fasteners. I would not go with pins any less than 0.25" ~ 0.27" diameter. A lot rides on the thicknesses of the joist seat and the beam top flanges, as well as the aforementioned wind loading concerns.

Make sure you consult with fastener manufacturer, applicable Steel Joist Institute manuals, and the Engineer before undertaking this alternative route. It has to be much faster than welding every single roof joist seat, as well as avoiding starting a fire in the existing roof construction.

You might also want to consider bolting some steel plate and angle or channel stock at strategic connection points. You can drill oversized or oblong holes to allow for expansion and some lateral movement. In structural repairs, a little extra steel can't hurt.... at least that's been my experience.

Where did you find stainless steel bar joists? Or are they homemade?

The plant has an outside contractor that does their pipe work fabricate them from an engineered set of drawings which they want welded. Everything is legit as far as standards go. They want the best for long term

They want to stop that ammonia, then!

I sure hope that someone is thinking ahead about installing new replacement metal roof decking, which must be highly resistant to the corrosive effects of the ammonia (gas?) in that building. Is this a manufacturing or gas production plant?

I'm assuming that the existing decking that's supporting the roof membrane is metal (steel & coated) and fully compromised. An alternative would be to install new RFP or HDPE decking of sufficient strength and sectional properties to span between the roof joists at the specified design Live & Dead Loads.

Has this even been addressed? Any further connections such as new steel plates and angles, and bolts & screws must be corrosion resistant as well.

Just saying....

Ammonia does not corrode steel, but it does eat zinc.

If ammonia does not corrode steel, what is the process that makes the base of lampposts corrode ? The assumption is that dogs pee on the bases and so create a very salty ammoniac cathode pool.

And does this apply to coastal locations too ? Always with respect to lamppost bases ?

To eliminate this SS to CS welding situation...have you considered mechanically fastening CS (MS) cleats to the new SS joists/ trusses and then welding those cleats to the beam?