Welding stainless to mild steel

[Conrad_Turbo]

I have a job coming up where I need to TIG stainless exhaust tubing to a mild steel flange. I recall hearing using 309 filler rod for welding stainless to mild steel. What are the benefits as compared to welding with 308 filler? Less prone to cracking?

I'm assuming the tubing is 304 stainless.

[Fat-Fab.com]

Excellent question.
TJ

[Conrad_Turbo]

Excellent question.
TJ

Excellent answer.

Well the reason I ask is because I have a lot of 308 filler and I don't think I will do a lot of stainless-mild steel welding (I've never been approached until now). The local welding outlet charges (for some reason in Sask we get charged A LOT...) for 309L filler 1/16" = $25.07/lb and 3/32" = 23.92/lb. Now I'm just wondering if I can get away with 308 unless it's an absolute no-no.

[bigo]

go for it

I use 309an 308 both when welding s.s to m.s, as far as ive heard your ok as long as you dont step down an alloy an you get penetration. I weld on fertilizer blenders that hold 10 ton an have never had a problem with welds failing. You should be fine.

[pull-do]

I know here at work, all of our procedures require the 309 filler for the SS/ CS weld, but I think the 308 or 316 will work just fine on that application, ------but that is a good question, I'll have to ask our pressure equipment guys.

[Fat-Fab.com]

I to use 308-308l for most all of my SS/MS work. I have not had any issues, I don't "know" that is the correct filler or not. On the other hand everything I have welded with it has not be "life safety" at all so I feel ok about it.

TJ

[calweld]

Ok, now read a couple of my other recent posts, we all know I'm a "hack" (and also a fruit and a nut ), willing to get away with whatever I can, also read my disclaimer below, I take no responsibility here. I'm not going to get too specific here, again, not sure how long the statute of limitations exist, nobody can prove anything.

In the years past, I have welded, patched, and built up many 90 degree and 180 degree SS pipes, carrying abrasive material and steam, at pressures ranging from 300 psi to 500 psi, heat and form 1" 1045 steel along the outside of the bend, then weld with plain old 7018 rod, never a problem (and no, 7024 didn't work here, tried it).

[Conrad_Turbo]

Cool thanks for the advice guys.

I get killed around here for filler prices, material prices...heck anything to do with welding... I'm going to be ordering a lot more of my welding items even more now through the states since the Can. dollar is so good.

After reading these posts I decided to weld it up with 308 filler (all the stainless-stainless pieces) and then autogenous welded the mild steel to stainless around the inside of the flange. On the outside I put three evenly spaced 1/2" long welds using 308 filler. There is no real physical loading on these parts, but there is heat cycling that is my concern for using 308 instead of 309.

I'm still interested why 309 is recommended in this case as compared to 308. I just can't justify those spending that amount on filler prices here for a job that might come up once in a blue moon.

Edit: Here are the shots:




PS I was only paid to do the welding, not the fitup.

[pull-do]

I still believe you'll be fine using the 308, why don't you do a search on the make-up of 308 vs. 309 on some of the manufacturers sites or where ever the write ups are.
I know out here at the plant, we are required to use the 309 on the process piping welds, but I've done some quikie welds on non-process stuff for all kinds of people with no complaints.
Don't really care for the way 309 runs either, but you have to follow procedures.

[Conrad_Turbo]

I still believe you'll be fine using the 308, why don't you do a search on the make-up of 308 vs. 309 on some of the manufacturers sites or where ever the write ups are.
I know out here at the plant, we are required to use the 309 on the process piping welds, but I've done some quikie welds on non-process stuff for all kinds of people with no complaints.
Don't really care for the way 309 runs either, but you have to follow procedures.

Well that's good to hear. I had the feeling since 309 is recommended for stainless to mild steel welds, by me using 308 it was like using a coat hanger to weld mild steel. But if you guys have done it without a problem for non-life critical stuff, then it should work just fine for this application.

I will find some time to dig up the differences between 308 and 309 when I find some time.

[JTMcC]

309 has higher levels of nickel and chrome to compensate for dilution when welding ss to cs. It's recomended for a lot of general purpose type ss to cs welds but when you add high operating temperatures and (or) different chemicals to the mix those dissimilar welds get pretty complicated and high nickel or one of the inconels or other specialty rods come into play, plus post weld heat treat, buttering techniques, ect.

But for run of the mill ss to cs weld, 309 is the common recomendation because of the additional alloying elements. I've seen autogenous welds between ss & cs being strictly forbidden because of that fact.

To each his own, but joining dissimilar metals is not the place to try to be cheap about consumables. In fact I don't think there is anyplace do that. A small amount of rework will quickly slay any money saved by not buying the correct rods, and the resulting potential for a damaged reputation isn't worth it to me. Consumables are very cheap compared to labor.
My opinion only.


JTMcC.

[Cracker(Jack)]

I believe the 309 is for corrosion resistance against the product running through the line, acid for instance. Otherwise, it works fine. Just my opinion.

[precisionworks]

I emailed Harris/Welco with that question ... here's their response:

Carbon levels in the steel cause cracking. 309 has a higher carbon content which is what you want when welding to a high carbon. You could also use 310 and 312. The 308 has a much lower amount of carbon and cracking could be a problem even with the preheat that would be needed.

If you have any additional questions, please let me know.

Thanks

Gina Lawson
Customer Service/Inside Sales Rep
The Harris Products Group
a Division of Lincoln Electric
ph# 800-733-4043 X6043

[JTMcC]

I emailed Harris/Welco with that question ... here's their response:

Carbon levels in the steel cause cracking. 309 has a higher carbon content which is what you want when welding to a high carbon. You could also use 310 and 312. The 308 has a much lower amount of carbon and cracking could be a problem even with the preheat that would be needed.

If you have any additional questions, please let me know.

Thanks

Gina Lawson
Customer Service/Inside Sales Rep
The Harris Products Group
a Division of Lincoln Electric
ph# 800-733-4043 X6043

I'd maybe run that by Gina again, maybe she didn't understand the question.
Or maybe I'm not understanding.
But if you compare required rod composition, as per AWS A5.9 or ASME SFA-5.9, the max. % of carbon allowed in 308, 309 or 316 is the same, that is .03% max carbon content allowed , an identical spec for all three rods.
In fact every spec (cept Mo where the 308 and 309 spec is identical, only 316 differs) is the same (MN 1.0-2.5%, S 0.03% max, Si 0.30-0.65%, Cu 0.75% max, Mo 0.75% max for 308 and 309/ 2.0-3.0 for 316) until we get to chrome and nickel where 309 has more than either 308 or 316.
That info is for tig consumables but I'm pretty sure you'll find that the required % of max carbon in the 308, 309 and 316 stick rods is identical at 0.04% max.

The increase in chrome and nickel is for the reasons I posted earlier.

JTMcC.

[djbtech]

309, 309L, 309LSi aren't necessarily beneficial as they are required for dissimilar metals such as 304 to mild steel. L and LSi just exhibit better corrosion resistance

308 is less suited for corrosion-resistance(such as soot/moisture formed in exhausts) 308 is specified for cross-stainless alloying

308 filler on stainless to mild steel has been shown time and time again to exhibit more cracking than 309 or 316

I'm sure those parts aren't load-bearing or subjected to chemical flow; they should be fine. I would suggest shooting for 309 in the future. You don't want cracking, especially at a mild steel flange.