Welding food equipment

[thecolin]

Does anyone out there have any tips or resources on welding stainless for brewing? I've got an industrial welding shop, we work on various metals from about 1mm to 5mm thickness, so equipment is not a problem. Almost all of the stainless we work on is AISI 304, which as far as I understand, is considered food-safe, so materials shouldn't be a problem. But I've never done any welding for something that contained food, anything I should be looking out for? Are there any processes/chemicals I should be using/avoiding? I'm thinking of throwing together a stainless fermenter, but I want to be clear on options and methods I may not be aware of before I get started.

 

[JasonInBTR]

I am not a welder but I have heard the term "sanitary weld" thrown around. A google search might reveal some info on the procedure.

 

[longwaytofall]

Well, all you are trying to do is not allow any pores in the weld. If you can lay a fat bead down, and grind it smooth afterwards, that should provide a smooth surface. Contamination in the form of the rod or part touching the tungsten is also going to be bad (I would think so anyways, tungsten is partly radioactive, and I wouldn't want it on the inside of my brew equipment). Personally, I would just lay an oversize bead and grind it smooth, then go over it with some very fine sandpaper.

 

[Ohio-Ed]

Sanitation is the concern. You don't have to worry too much about welds that come in contact with the wort before the boil because the boil will kill any bacteria that is introduced. However, after the boil you have to be able to sanitize any equipment that comes into contact with the wort.

A lot of folks use heat or chemicals to sanitize their equipment. If you can get the equipment hot enough for a long enough period of time it is pretty effective. I ferment in sanke kegs and boil about a gallon of water out of it to "steam clean" and sanitize the inside.

Chemicals are very effective at sanitizing equipment that you cannot heat sanitize.

The problem with welded equipment is that if the portion of the weld that comes in contact with the wort has ANY cracks, gaps, craters or pores they are very hard to clean/sanitize.

In my opinion, a fermentor is a pretty ambitious place to start learning to weld brewery equipment.

There are several threads here with discussions about welding Stainless Steel, I'd suggest you read through them for input.

Good luck,

Ed

 

[thecolin]

Thanks for the info. We do a fair number of oil/water tight welds for machines and oil cooled transformer cases that need to be perfectly sealed. But those are big enough for six people to stand inside, welding and finishing the inside of a 20 liter fermenter is going to be a bit more annoying, logistically speaking. =P

I have in fact searched the forum a bit. It seems there are a lot of threads with people trying to find out what type of process to use to weld stainless or looking to weld things onto existing kegs, which isn't really what I'm looking for. Thanks for the suggestions, I'll keep looking around a bit.

 

[kladue]

Since you are familiar with stainless steel welding the only things I can add are the finish on the welds needs to be as smooth as possible, and after any welding or grinding the stainless will need to be re-passivated. A handy setup for polishing welds is the 3-M hook&loop adapter for a 4" grinder and the blue and gray disks, quick change when pads wear out. Using coarser pads (maroon, green) leaves scratches in the surface which is not a good thing and it takes some effort to buff them out.
If you want the ultimate inside finish send the finished fermenter to some one who does "electro discharge polishing" and the inside will shine and be passivated at same time.

 

[thecolin]

Thanks kladue, that's useful. Getting some of the smaller finishing tools for a dremel might be useful as well?

I've been trying to teach myself how to do high gloss finished by hand in my spare time (since it's not something we do for clients). Fermenter with an inside mirror finish anyone? Yeah... maybe not. =P

 

[HumanGarbage]

Kladue is right on the money as usual. Walter makes a similar disc system if you can't find the 3M. Its what I roll.

TIG is the process of choice. Done properly there shouldn't be any need to really grind anything- the finished weld should not be porous anyway.

Be sure that your welder back purges the weld. If you don't have argon on the backside it will sugar (think REALLY porous). Hard to deal with inside a small vessel...

 

[mikelikesit2000]

Welds in food service should be flat and or smooth on the inside. If necessary use a backing gas (argon) to prevent backside from sugaring

 

[kladue]

If you get into a situation where back gassing is not possible there are 2 products I know of for protecting the offside of the weld, "Solar Flux" and "Superior #9". These are powders that are mixed with alcohol or water and painted on the weld area as a thick slurry, the fluorides in the flux keep the stainless from sugaring, and it forms a glassy covering like stainless stick rod does. A stainless wire brush in a 4" will usually knock this off after welding, or a flap wheel will do the same.

 

[Hermit]

Not sure if greenmonti still comes around. Search his name. Good info.

http://iam.homebrewtalk.com/GreenMonti

 

[chady74]

yes back gasing is a must on stainless im a welder pipe fitter and work in a lot of food and beverage plants and we always back gas our welds and they come out perfect every time nice and smooth no grinding needed

 

[GreatWetNorth]

As a welder and someone looking at putting a new brewing set-up together, I'm in a similar position to you. My TIG skills aren't great and the stuff I do at work doesn't need to be sanitary, but I know enough that I can share my somewhat qualified (though not expert) opinions.

kladue suggested a couple of products as an alternative to back purging. I haven't used Superior 49 before, but I have used Solar Flux. It works fine and I was considering using it, but their website recommends back purging if you're doing anything food-related. That's not to say it won't work; their warning may be more a matter of liability, and if you can wire brush the residue off after welding you might be ok. However, if you're going to the trouble of fabricating and welding your own equipment, you might as well take the time to properly back-purge.

I can't really disagree with any of the comments about grinding your welds smooth (and I've ground more than my fair share of welds smooth at work). However, rather than planning on laying down a big weld and grinding it smooth afterward, I would concentrate on things that will help you get a nice weld that doesn't require any grinding (like practicing your TIG, along with getting a nice fit and cleaning your pieces really well). Along the same lines of my comment about back purging, if you're going to do it, do it properly from the beginning (or at least try your best). From your posts, you're obviously either a welder by trade, or you work with welders, so getting a sound weld shouldn't be too difficult. With back-purging, practice and good fit, you should be able to get proper penetration and have a nice bead inside and out.

I'm not trying to look down on anybody who talked about grinding after welding, and it probably would be a good idea to stock up on some of those abrasives mentioned earlier. But I find that whenever I do anything that has to turn out "nice", I would much rather spend extra time before-hand to make the job as easy as possible, rather than try to clean up a mess afterwards. Again, just my qualified, but not expert, opinion.

 

[dmfa200]

I hear a lot of responses on re-passivating stainless steel after welding. I think the concerns are out of anal-ness or paranoia.
If you use tools and abrasives that have not been used on anything other than stainless steel there is little to worry about. Stainless steel will re-form it's protective oxide layer on it's own immediately.
One measure that must be taken is that the discoloration after welding promotes corrosion and must be removed. The easiest method is simply a stainless steel wire brush. Give the weld a few minutes to cool, and while it is still hot brush the discoloration off to bright finish, and this will do the trick.
I've been welding stainless for close to 15 years and have never seen any corrosion problems following these simple guidelines.
Your main concern is impregnating stainless with free iron. As long as you use clean tools and abrasives you will not have corrosion problems.

 

[ScubaSteve]

BKF is also a good way to clean the gunk out before coming in contact with wort....and it repassivates as well.

 

[Ohio-Ed]

I'm not a welder, but I'm reading everything I can on the subject and learning as much as possible. I bought a tig welder and hope to be able to weld stainless brewery equipment someday. You are obviously light years ahead of me, but here is my thoughts;

I think the key is proper preparation of the weld (cleaning and fit), back gassing or purging, correct filler, and correct current/heat. Also, as previously posted, don't use tools that have been used on metals other than stainless or they can contaminate your weld.

Grinding / cleaning / re-passivating are means to correct a less than perfect weld. In some cases, those techniques are not practical... Imaging trying to grind the inside of a sanke keg. I think before you take on building a fermentor, your techniques should be very sound and beyond fixing your welds.

When I get to the point of welding any of my equipment, I will spend a lot of time working on "Pre-Boil" equipment to work on my technique.

Good luck,
Ed

 

[P-J]

Ed,

You are absolutely right on the money with your comments. Just thinking about the dairy industry, everything is SS and all of it is sanitary welded. It's impossible to grind/clean a weld inside a 30+ foot 2" OD butt welded SS pipe line. Nevermind the connection points. The weld itself must be flawless from the start.

I really like your thinking.

 

[thecolin]

You are obviously light years ahead of me...

I only wish that were true, in fact I'm a part time welder, full time general metal worker/office administrator/father. And I'm trying to do all of it in Italy in a language I am still learning. In other words, my welding needs a lot of improvement. A lot of the welding we do at work is pretty fast a loose; industrial production stuff that often can't afford the time for a perfect weld. Ninety-nine percent of the TIG welding we do is without any kind of filler material as well. On the plus side, it really teaches you to line your pieces up perfectly, or there will be holes-a-plenty. On the down side, it's not really a technique that would work at all on this kind of project. I'm teaching myself to weld with filler material when I have the time, and hopefully I'll actually take a welding course in the future. I'll get where I'm going eventually, even if it'll take me a few decades.

What you said makes a lot of sense, I'll keep it in mind as I try and work something out.

 

[chady74]

good for you learing to weld on your own time the biggest thing with ss is to prep it right and make a good fit then purge it realy good the cleaner the better and like dmfa200 said brush it realy well wile hot you should not have any problems i learned on plate steel befor i learned ss pipe so just take your time and you will get it

 

[chady74]

i will post some pix of some welds i did a few day ago on the bench for a local brewery just a 3" product line fab up but you can see how the inside should look when done right

 

[thecolin]

i will post some pix of some welds i did a few day ago on the bench for a local brewery just a 3" product line fab up but you can see how the inside should look when done right

That would be really useful, thanks.

 

[mikelikesit2000]

Depending on what you are welding, I would reccomend getting some pieces of flat sheet SS material the same gauge as what you plan on welding. Then you can pratice your free-hand tig welding. I would butt 2 pieces together solar flux the backside and "fuse" them together. You may need to add a very small amount of wire to get going with out opening a hole but after that you should be able to travel along steady with out adding any filler wire.

Oh and by the way, I am a pipefitter welder in a Nuclear Power Plant. I takes years to be a decent welder, and even longer to be a great one. As has been said before, Really focas on the fitup, for thin sheet metal you dont want an gaps.

 

[noiz2]

Contamination in the form of the rod or part touching the tungsten is also going to be bad (I would think so anyways, tungsten is partly radioactive, and I wouldn't want it on the inside of my brew equipment).

Two points of correction. Contaminating your Tungsten is bad not because tungsten gets in the SS but because gunk on the tungsten will make for a very sloppy overheated weld. And tungsten is NOT radioactive. You can get thoriated rods that are very slightly radioactive but it's the thorium in the alloy that is radioactive. The rest of the rod alloys are not radioactive at all.

 

[Bobby_M]

Two points of correction. Contaminating your Tungsten is bad not because tungsten gets in the SS but because gunk on the tungsten will make for a very sloppy overheated weld. And tungsten is NOT radioactive. You can get thoriated rods that are very slightly radioactive but it's the thorium in the alloy that is radioactive. The rest of the rod alloys are not radioactive at all.

The half life of this thread was 4 years.

 

[day_trippr]

The half life of this thread was 4 years.

^Post Of The Week^

 

[noiz2]

OK but Thorium has a half life of 14.05 billion years ;~)

 

[Kee]

Funny, I don't remember being warned about this in TIG school:

"The Thorium used in 2% thoriated tungsten is a radioactive element and therefore can be dangerous to the health of those exposed to it and to the environment. ... ...during the grinding of electrode tips there is generation of radioactive dust, with the risk of internal exposure."

 

[noiz2]

It's a hot topic now though. The only real exposure is when grinding the electrode, and there are so many other electrodes to choose from. There seems to be a limited old school bunch of folks who are in love with them but they don't in tests seem to have any advantages over the alternatives. But my point was you don't touch the electrode to the work in the first place (intentionally anyway) and you are not imparting radioactivity into the weld. Breathing the dust from grinding electrodes isn't a great idea in any case and the thoriated one probably more so, and if you are not capturing the dust you will be tracking it everywhere. But the rod is not particularly radioactive so the danger is really to professionals who over a career might pick up significant exposure. Most of the old school argument sounds like the old smokers argument, "I been doing for years and I'm fine". In both cases it is not a valid argument because all of these things increase your "risk factor" none generally have a causal relationship. So if you have say zero chance of getting X a 100% increase of your risk factors is not a worry. But if you have a 50% chance of getting X a 100% increase is something to worry about. I haven't seen any studies that gave a risk factor but it's probably less than that of breathing metal or flux fumes and who wears a respirator all the time.