[Rick_H]

So I have a piece of equipment that sorts and loads plastic bottles for the industry. It can be a little violent at times due to the bottle size and or the rpm of the drum. It tends to crack a welded joint fairly often.

I prefer to re weld them, 304L with 308L filler. One of my counter parts has been silver solder them. Always makes it fun for me to repair those.

What I'm wondering is by getting the 16g stainless red hot to apply the solder, is it contributing to the subsequent failures. In my mind yes.... Was wondering what you guys think? This will be a touchy subject if I bring it to light but knowing what I think I know it has to be an issue.

[weldin mike 27]

In my limited knowledge, it's not advisable to keep ss too hot for too long. Whether the soldering takes place in that temperature range is the question. There is lots of talk on here about soldering ss pipe fittings. What join are you talking about?

[Rick_H]

Mike, it's a special pocket that holds a bottle, OEM are welded joints but they grind them nice and smooth and pull some meat out of them. Its an outside corner joint on a special shape.

I'll grab a picture tomorrow...

[weldin mike 27]

I'm sure Otto will bring better info, but in the small area of expertise, ss is usually welded, I can't say I have seen a silver solder join. There has to be a reason for that.

[Rick_H]

I'm sure Otto will bring better info, but in the small area of expertise, ss is usually welded, I can't say I have seen a silver solder join. There has to be a reason for that.

My coworker is using the silver solder due to the ease of repair and his level of skill with a welder. I weld them up with no issue, same as OEM...

[weldin mike 27]

hope you can get better info than my waffle, (oh and I meant to say, "my small area of expertise"

[Coldman]

I'd like too know too. I have to silver solder copper tube into 316 stainless steel connections to plate heat exchangers from time to time and you have to heat the 316 to red to get the solder to do its proper run thing. I have always wondered what damage if any was happening.

[Rick_H]

I know solder joints can be very strong, over 70,000psi but most of those joints are a lap type setup like pipe, not a fillet or outside corner. It has its uses, and is actually food safe hence why some brew guys use them as they will not have to have a tig and purge setup.

[exnailpounder]

Rick, I don't know if this will help you out but one time I Silbrazed a SS fitting to 18ga. SS ( coupler to a beer keg) for a homebrewer guy. I leak tested the fitting and it did not leak. He took the keg home and called me a few days later after boing water in the keg to sanitize it and said it leaked like a sieve. He brought it back and I ground out the fitting and weld to the parent material and it was stressed cracked all over the place in the HAZ. Admittedly I went a little heavy on the braze to make sure it held and I must have kept the area too hot for too long and it cracked badly. I welded in a patch and a new fitting and no more problems. When I weld on thin SS I only run a bead about an inch and stop and lay a wet rag near the weld to draw out heat. Thin stainless can be a PITA.The only reason I brazed the fitting in the first place was I didn't have the means to back purge at the time. Now I have an extra bottle just for that. Now I weld only and have never had any more problems. Hope this helps....Jeff

[Markus]

Is the base metal L-grade?

[Rick_H]

Is the base metal L-grade?

Yes Markus everything I can find is it is 304L

[LtBadd]

I'd like too know too. I have to silver solder copper tube into 316 stainless steel connections to plate heat exchangers from time to time and you have to heat the 316 to red to get the solder to do its proper run thing. I have always wondered what damage if any was happening.

That's why when I braze I'm always generous with the flux, still when you get close to the brazing temp you can't afford to dwell with the torch, that could easily over heat the area

[LtBadd]

I'm sure Otto will bring better info, but in the small area of expertise, ss is usually welded, I can't say I have seen a silver solder join. There has to be a reason for that.

My coworker is using the silver solder due to the ease of repair and his level of skill with a welder. I weld them up with no issue, same as OEM...

Are the braze joints the only ones failing?

[Rick_H]

Are the braze joints the only ones failing?

No, the OEM welded joints do fail at times, but I am not finding ones that I've welded broken I do leave a little more meat to the bead then the OEM. I am finding I am repairing the silver brazed ones often. After break I'll be working on some I'll snap some photos.

Getting all the silver out of the joint after they been repaired it quite time consuming, and it aggregates the hell out of me if I hot some while welding

[Otto Nobedder]

Stainless steel is red-hot when it's formed and worked at the foundry.

It amazes me that people think it's bad to get it hot again. Surface oxides are the only thing to control, and that's done with the atmosphere it's in, or the post-treatment if there is material to sacrifice.

I regularly silver-braze 304 to red brass/bronze using O/A, and yes, to do it right everything reaches brown-dull red. I've never once sugared a SS nipple in this process, despite NO backpurge and NO flux on the inside of the SS nipple.

Worry never solved a problem, it only distracted from the solution.

Steve S

[Rick_H]

Stainless steel is red-hot when it's formed and worked at the foundry.

It amazes me that people think it's bad to get it hot again. Surface oxides are the only thing to control, and that's done with the atmosphere it's in, or the post-treatment if there is material to sacrifice.

I regularly silver-braze 304 to red brass/bronze using O/A, and yes, to do it right everything reaches brown-dull red. I've never once sugared a SS nipple in this process, despite NO backpurge and NO flux on the inside of the SS nipple.

Worry never solved a problem, it only distracted from the solution.

Steve S

Steve, I just wonder about multiple repairs of the same joint and multiple heat cycles? My assumption is the heat isn't the issue, its the design of the joint and brazing not being an ideal solution.

[LtBadd]

Stainless steel is red-hot when it's formed and worked at the foundry.

It amazes me that people think it's bad to get it hot again. Surface oxides are the only thing to control, and that's done with the atmosphere it's in, or the post-treatment if there is material to sacrifice.

I regularly silver-braze 304 to red brass/bronze using O/A, and yes, to do it right everything reaches brown-dull red. I've never once sugared a SS nipple in this process, despite NO backpurge and NO flux on the inside of the SS nipple.

Worry never solved a problem, it only distracted from the solution.

Steve S

Steve, to that I'll say two things, when you braze you don't reach the same temp as welding (TIG) and getting the stainless hot (too hot) can reduce the corrosion resistance.
I'm not saying you are doing this with your braze op, and not knowing how thick the nipples are, it may beneficial to have flux inside

[Markus]

Stainless steel is red-hot when it's formed and worked at the foundry.

It amazes me that people think it's bad to get it hot again. Surface oxides are the only thing to control, and that's done with the atmosphere it's in, or the post-treatment if there is material to sacrifice.

I regularly silver-braze 304 to red brass/bronze using O/A, and yes, to do it right everything reaches brown-dull red. I've never once sugared a SS nipple in this process, despite NO backpurge and NO flux on the inside of the SS nipple.

Worry never solved a problem, it only distracted from the solution.

Steve S

I agree and disagree with you Otto. Yes they do heat metal to red hot at the mill and keep it pretty long in those temperature, but the difference is that they also heat treat coils after that. Rapid cooling done by water immersion or so. I think it's called annealing with austenitics grades.

Keeping austenitic stainless steel long in high temperature and you end up with sigma phase for example. In sigma phase carbon will form carbides with chromium atoms in the grain boundary. This will weaken the structure and there is also risk for intergranular corrosion.

Here is some facts from Euro Inox:

Sigma phase.png (227.84 KiB) Viewed 713 times

[http://mobile.euro-inox.org/map/intergr ... rosion.php]




Can you braze or solder stainless steel then? Yes you can, but you have keep those metallurgical facts in mind. Specially if parts will be under stresses and or harsh environment. As said L-grades help a lot preventing sensitization. It will happen in time, but you have to keep steel very long in that certain temperature, 10 min or longer.

How to get ridd of those carbides etc then??? At mill they heat metal to very high temperature, over 1000 celcius. Then those phases are dissolved and everything is in form of austenite. Then they cool it down and depending of the alloying elements they will end up with little ferrite or non at all.

[Markus]

Here is little article from Euro Inox guide, Working with stainless steel. Can be read or downloaded from here http://www.euro-inox.org/pdf/map/Workin ... eel_EN.pdf

Soldering.png (445.67 KiB) Viewed 712 times

brazing.png (97.55 KiB) Viewed 712 times

[Markus]

So I have a piece of equipment that sorts and loads plastic bottles for the industry. It can be a little violent at times due to the bottle size and or the rpm of the drum. It tends to crack a welded joint fairly often.

I prefer to re weld them, 304L with 308L filler. One of my counter parts has been silver solder them. Always makes it fun for me to repair those.

What I'm wondering is by getting the 16g stainless red hot to apply the solder, is it contributing to the subsequent failures. In my mind yes.... Was wondering what you guys think? This will be a touchy subject if I bring it to light but knowing what I think I know it has to be an issue.

To me soldering or brazing is not an issue here. Real issue to me seems to be the choice of wrong material and also perhaps wrong design. As you Rick already mentioned.

You mentioned high rpm's etc. Austenitic steels tends to be pretty prone to cracking under quickly changing stresses/loads. Perhaps ferritic grade would be better choice in this case as it is almost immune to stress corrosion cracking.

[Otto Nobedder]

Markus has given me a great deal to digest.

To summarize my reply to the original post,

Silver-solder strength is directly proportional to the surface area the silver can cover. It makes an excellent socket joint.

It will not make a good butt joint.

Steve S