Underway: Project "S.S." = Super Sport = All-Stainless Insulated Cabinet Build

[MisterChrister]

I'm FINALLY getting around to building the all-stainless insulated cabinet smoker that I've been dreaming about for years! I used to run a custom millwork shop, so measuring, marking, jigs/fixtures, tools, and exacting tolerances are no sweat; but translating those skills from wood to metal (especially stainless) is another story! I have VERY little metalworking experience, but I'm determined to patiently learn as I go. I have a few questions for experienced metal fab guys (or gals!), especially those who've worked with stainless a lot.

Basically, this was a liquid carbon dioxide storage tank that I got last year, specifically for this project. It's actually a tank within a tank, all food grade 304 stainless construction. The outer shell is approximately 26x50, and the inner (thicker) pressure vessel is roughly 24x47. I'll know exact dimensions when I get in there. The plan is to make a large door on top for access to the cooking chamber/grate area, and a smaller door below to access the fire basket. I'm planning to have a 3/8" thick diffuser plate/baffle full of drilled holes between the fire and cooking chambers.

First, I need to deconstruct what's here. I need to make a cut all the way around the circumference near the top, remove the inner vessel and the pipes that go in/out of it, as well as the cold-rated insulation from the air space between the tanks to replace it with rock wool. This brings me to my first question:

I'll be mig welding this all back together (.030 / 308L wire with tri-mix gas). Since this tank is definitely 304, the manufacturer PROBABLY used 308 filler metal when they fabbed it 20+ years ago, but they no longer have the spec book from back then (I checked), and can't guarantee it; it's possibly 347 filler, or even something else. Not likely, but not impossible. Will I be ok to split the dome top of this off right AT the existing weld, do my stuff inside, then weld back to the old weld seam, hoping it's 308 like my new wire? I'm thinking this is pretty much a multi-pass weld, just with 20 years between passes! Will it bond good enough for what this non-structural project is, even if it's not the same material in the old and new beads? I'd rather not have two welds really close to each other at eye level (all the way around the tank like twin racing stripes!) if at all possible, but will live with it if it means not having my welds pop loose later.

Next question is regarding the material to join the inner and outer vessels together at the doors & door openings; "jambs" if you will. As I mentioned, the inner vessel is thicker than the outer. How important is it to make the "jamb" material the same thickness as one or the other vessels? Should I split the difference so I don't risk burn-through or under-penetration by having my current set too high or low? The outer skin is approximately 3/32" and the pressure vessel inner tank is probably closer to 5/32" or even 3/16", if that helps.

Last question for tonight, and probably not as much of a question as I'd like, as I really don't know what other options I have at home in my garage. Are these cutoff wheels going to be ok? I thought I heard somewhere that you can overheat stainless and actually cause it to rust if you're not careful how you cut it. I can't see using any sort of cutting fluid to reduce friction and heat while doing all of the cutting I need to do. That said, if someone in the know tells me "dude, you're going to screw up the whole point of stainless with an angle grinder and those wheels, dry", I'll try REALLY hard to go another route. I REALLY want this project to be done just right, the first time. I don't have access to a huge bandsaw, water jet, etc., but could MAYBE muster a plasma cutter if my current plan is a definite "no-go".

If y'all have any other ideas or thoughts, I'm all ears! Thanks for any help or insight you can offer, and PLEASE have patience; this thread is going to be around awhile before I'm finished as I'm REALLY short on free time for projects! Oh yeah, please forgive me Mopar & Ford fans - I'm a "Bowtie 'til I die" guy, so "S.S./SuperSport" seemed appropriate, especially for an All-SS rig! :mrgreen:

 

[Stlsportster]

Sub'd

 

[4ever3]

That's what I'm TALKIN' about!!

Are ya done yet?

 

[Q Junkie]

Some of those tanks have a swaged bell end, meaning that there is a narrower portion of the bell that drops into the tank and the weld is on a lap joint. So if you cut through the weld or just below it you will be cutting through possibly two layers of stainless.
I can't tell by your pics but look at where the bell end meets the weld and see if there is a slight inward roll of the steel. If so it might be lapped. The weld will also be harder to cut through than the tank material. I know its not aesthetically pleasing to look at but cutting just below the weld and only through the outer wall is way easier some times and will leave the inner lip in tact.

 

[MisterChrister]

Thanks, Q Junkie! It's exactly THAT kind of expertise I'm hunting for here!

Jeremy, get on over here and we'll have it done by morning! I pay in cheap pizza and REALLY good beer!

 

[Q Junkie]

I vote for an RS/SS paint job on that beast. :clap2:

 

[MisterChrister]

Q, you may be right. Looks like the end of the dome piece is rolled where it dives off into the weld. This is much better to figure out now! Would you guess that it's lapped even farther than past the bottom of the weld?

 

[Q Junkie]

Cutting just below the weld and leaving the inner wall in tact will help with welding the tank back together and keeping it nice and round. You could always drill a test hole somewhere in what will be the back to find how far the lap goes below the weld. Should be easy to spot weld a small test hole or two and grind/polish it away. Trying to butt weld that tank back together would be a challenge for an experienced welder so keeping the lap is a good idea.

 

[Hillbilly BBQ]

Will keep an eye on this

 

[ebijack]

Are you stuck with using a mig? Using a tig, you could cut thru the center of the weld and carefully tig that same weld back together using very little S.S. rod at all. You can do a much smaller/thinner weld with less weld material, Your not looking for the same pressure requirements that it was built with. You will be losing the thickness/height of each cut also out of the weld area.
For exact and thin cutting, I prefer either a 1/16" 3M green wheel on a 90 deg air grinder or a sawzall (used properly, not like everyone thinks). Use a black or blue marker, or bluing if you have it since it is easier to remove when done. Scribe your line all the way around. Put at 3 vertical location marks spaced around/across your cut line so you can place the pieces back to the exact same location when ready to weld back together.
You do not have to worry about metal thickness concerns for what you are doing about making door access.
Once tacked back together, place the tank sideways on either upside down furniture dollies or similar for ease of moving/rolling the tank as you weld. Set up on a table makes for less back strain and nicer weld.

 

[4ever3]

Q is 100% right, the ends are swaged in and cutting in the center of the bead would be best but the material would be twice as thick. That being said the end product would look better because your bead would be on top of the OEM as opposed to welds laying side by side.

Jack is also right about the 3M green, they'll cost you more up front but they will outlast 2 or 3 of the other wheels!


Be sure and put a clocking mark on the taken and bottom so you can realign the when you weld them back together because no matter how hard you try the will be waves in your cut.

To bad you can't bring it here, I tig for food :wink:

 

[MisterChrister]

I ended up cutting it just below the weld. It doesn't look too much like an angry beaver attack, so I guess that I'm happy enough.

The insulation in the airspace between the two tanks ended up looking like layers of toilet paper and aluminum foil! It was like a weird kind of reverse Christmas present wrapping on the inside LOL

Here's how the two tanks fit together. The post on the bottom of the inner vessel sits inside of the socket at the bottom of the outer shell tank. It's designed to carry the weight of the tank + 600 pounds of liquid CO2 inside, so I'm sure it's strong enough to use it for a smoker!

And here's the piping manifold that I'm working on taking off. I ran out of cutoff wheels, so I guess I'll have to chip away at this during the week if I get any time! Now that I say that, it's pretty unlikely. I commute over an hour each way for work every day, so by the time I get home from my 8 or 10 hour shift I'm usually pretty shot. Hopefully I can get a bunch more done next weekend. I'll post pictures as I go along.

I almost forgot to mention, the inside diameter of the inner tank ended up being just under 22 inches. Hopefully, I can use Weber kettle grates for the time being until I get to make expanded stainless cooking grates. That chit is expensive, so it might have to wait and this'll give me that option for the time being.

 

[TuscaloosaQ]

Your biggest challenge in this whole job will be distortion... Stainless will move ...shrink. And distort very easily.. I have fabed and welded miles of stainless pipe and pressure vessels..mig with tri/ mix gas will give you less distortion when welding... Tig/ heli-arc.. In the hands of a experienced welder will give you a slicker prettier weld.. And like mentioned if you have a good fit up you can fuse the metals together using very little filler metal.... Especially on a lap joint... Heli-arc distorts the metals easier because you have high intense heat in a concentrated area longer... Be sure and take extra time to clean and prep all the weld joints before hand... I would not be afraid to cut what you need with a metabo/ cutoff wheel as long as it had not been cross contaminated with carbon steel... Looking great so far!!!!

 

[TedW]

Good looking build