Jeremy, I have found the thicker the better for the pipe, but in the end it is all about the welding. Not all stainless are the same and obviously the greater the corrosion resistance, the better but carbon play a key role. The lowest carbon steel you can get it best and it is critical that you weld the stuff up with the appropriate low carbon rod. Because all of this I have used 316L stainless for years but have had issues with the cost involved, the stuff in insanely expensive these days (I am not exaggerating "insane" it approached prices of precious metals). Due to this and the requirements of a special purged atmosphere (inside and outside the pipe)to weld it. The last time I had a 3/8" thick 5" dia. bottom replaced it cost around $275 and most the the weld shops I approached couldn't handle it properly, I had to find a diary pipeline welder to do it.

To deal with this I am thinking of another route when I need a new tube- seamless. I have a stash of gas cylinders such as old SCUBA, SCBA (steel not aluminum) and other tanks that I may try taking the top off from and using since they have no welds to deal with. The stainless pipes will last a lot longer but when they need to be replaced the cost is now catching up with the benefits so I'm thinking of alternatives in low carbon steel that can just be replaced without going broke.

For low temp salts just about any thickness will will work and carbon steel is just fine, it is the high temp stuff that is the stickler.

Thanks for the information, I appreciate it.

Jeremy

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I'm planning on building a salt pot and am slowly gathering the parts. I was at the scrap yard a few weeks back and found some nice stainless tubing and a block to get it welded to for the base. Since then I started wondering what the thickness of the pipe ought to be-what should the minimum wall thickness be? My understanding is stainless pipe is used because of the corrosive nature of the salts and it therefore lasts longer than a plain carbon steel tube. Is 1/8" big enough or should it be a ways thicker (haven't measured it, but guessing it's around that or maybe 3/16")? Thanks for the help.

Jeremy

I've been building salt pots for some time now (mostly gas) and the problem with the pipe is not inside but out-the fire makes it scale that peals off and after a while wears thin-I used electric salt pots in the beginning but I was always burning the elements-no doubt my fault-but anyhow what ever the pipe you use your last responder was right thick if you can-but the weld is very important...also after you fire the pot-when you are through and turn it off the salt turns hard one of the problems is when you start up again the salt usually heats first at the bottom and there is a pressure build up and you may have trouble with the weld coming apart-So what I did was get a piece of steel about an inch and a half round and long enough to reach close to the bottom of the tube and tapered it from point to rear and put a hole in the top for a cross pin to hold it on the top of the tube.before the salt gets hard I put the tapered steel in the pot--before firing again I hammer the rod handle and pull it out and the salt melts from the bottom up with no pressure because of the hole the tapered steel pin left..Don Fogg and Howard Clark are the ones I learned about the salt pot-if Don's site is still up he's got a lot of info-good luck--

If gas eating the pot from the outside is a problem, has anybody tried coating the outside with a non-insulating refractory (like satanite)? Shouldn't that shield it from oxygen but not impair heating?

Just a thought.

Anybody care to comment on salt pot usage in high humidity environments? I've always wanted to build a salt pot setup, but am hesitant of the risks. My shop is not climate controlled (or controllable), and it's not uncommon for condensation to drip from the steel roof inside the shop in the early morning.

On my salt pot (gas) there is an exhaust pipe and right before I put the knife or whatever in the salt I lay it on the stack and that dries it out or if not you can run a torch over it......

I agree with Kevin on the 316L....it's what I use, and I am always cruising the scrapyard for suitable pieces.....but even at scrap prices it's crazy expensive. BUT...considering the fact that I've had 316L "tanks" last as long as they have (most last around 5-6 years) it makes the sting of the price a bit less.

has anybody tried coating the outside with a non-insulating refractory (like satanite)?

Over the years I've tried coating my salt tanks with various "stuff"...the problem is that nothing matches the expansion/contraction of the 316L, and whatever I've used "pops" off between heat up and cool down. That was me trying to be greedy, and make the tank(s) last even longer then they do...so after a while I just gave up on any coatings.

I have worked with both, carbon steel and 316L, for tubes. The carbon steel oxidized heavily and Don is correct that they will indeed scale until a pinhole forms at any given place from the outside in. The 316L is entirely different, it merely forms a dark gray oxide coating which stays unchanged for years, and any leaks I have ever had were from the inside out at the weld seams. This is, however, often related to the other issues Don brought up with the expansion of the melting salts putting stress on the welds. The tapered rod to form a chimney is not just a good tip it is almost essential with a gas fired unit; electric heat tends to melts the salts more slowly and uniformly. Some folks also dispense with the taper rod and use a very long auger/drill to cut the hole in the solid salts before firing.

Hello All;

I have a question? What dimensions or size of tank would you guys recommend. Would you make both Hi-temp and low-temp tanks the same size?

Russell

Personally, my recommendation is to use the smallest diameter tank, that you can fit the largest blades you ever intend to put into it. With salts you're dealing with thermal mass....what that means is that the accuracy of your temp control will be directly related to the "mass" of salt and the tank. My "tank" is 2 1/4" ID X 20" deep/long. With this tank I can keep the salts at +/- 10-12 degrees of set point. As you get larger in tank size, those numbers start to widen out, simply because of the thermal mass, and the "lag time" caused by heating and cooling of a larger thermal mass. Hopefully that makes sense, but as a further example, I was helping an individual via phone, build a tank, and he kept insisting that he wanted his tank to be 6" diameter. I tried to tell him that he would get extreme temp swings, but he wouldn't listen. He called several more times after setting up a 6" X 24" tank, asking me how he could make it more accurate (he was getting 50-100 degree temp swings). I kept telling him to reduce the tank size to 3" or less. I didn't hear from him for several months, then got a call from him....telling me that he wished he had listened in the first place. He finally had changed to a 3" diamater tank, and said he was able to hold +/- 20F of setpoint.

I know that might make it sounds really tricky, but it's not. Just take the time to think before you build, and consider the variables...there will always be a level of experimenting/learning, but that why we do what we do! <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

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Hello All;

I have a question? What dimensions or size of tank would you guys recommend. Would you make both Hi-temp and low-temp tanks the same size?

Russell

This is a really good point to bring up since the O.P. mentioned wall thickness as well. I'm with Ed on the high temp tube not being too big, here the fluctuation in temperatures from items added to the salts will require a quick rebound from cooling. Other contributing factors here are obviously the controller and the placement of the thermocouple. The low temp are another story, they need to cope with the heating effect of adding hot steel to them so they benefit form larger volume, but to offset the thermal mass effect on heat control you don't want a tick tube wall. It is oddly inverted, but on the low temp I have found thicker walled pipe to be a problem, but then carbon steel works just fine for low temp. It is also important to remember the agitation is even more critical with salts than with oils, not so much due to vapor jackets but to increase convective action. So you will need room to move your blades around in the salts if you do not move the salts themselves. Without moving the salts,the larger volume can add to the temperature swings more, depending on the thermocouple placement. Since I still run electric on the low temp, I run a dual thermocouple system and simply switch to reading the outside of the tube when I am doing things that will create temperature fluctuations.

Thanks, Ed and Kevin

Makes sense!