A pipe nipple and a low compression fitting are used to secure a K thermocouple inside of the thermowell within the center tube. Note that the pots are designed to sit on concrete blocks allowing clearance for the wires and thermocouples underneath the pots.
The top is just a piece of 1/4" plate with a hole cut in it. It is not welded to the inner or outer tubes. When you cut this hole, leave plenty of clearance for the salt tube to expand. Our hot pot may get as much as 2" longer than normal at 2000F ... and it gets rather larger in diameter. So cut the hole with lots of room, else your top will get a free ride upwards.
The burners are of Ron Reil venturi draft design., so no fans are required. A Pipe nipple is used as an entry port and hold for the burners. The pot used for high temperature only needs a single larger burner to bring it to temperature relatively quickly and keep it there. This is not true of the pot used for low temp salt. A big burner will bring it to temperature just fine, but we've had difficulty getting a low enough flame required to just maintain the temperature without blowing out. Therefore, we went to two burners on the low temp pot ... one for initial heatup and one for maintenance. The maintenance burner is rather small.
Notes on Salt Maintenance
The high temperature salt seems to build contaminants over time as they are used. If not cleaned or treated in some way, these contaminants result in damage to the surface of the materials being heat treated. This can range from mild surface etch in the beginning to very severe burning of the surface and can require extensive refinishing after the heat treating process. Mike Alexander has developed a protocol for cleaning the salt at each use which dramatically reduces this problem. Add a teaspoon of Boric Acid to the high temperature salt just as the pot if fired (NOT after it is already hot!!!!). Then use 4 or 5 carbon rods (we bought NOS arc welding electrodes for cheap) to stir the salts as soon as they melt. The rods are drilled and strung on a shaft to suspend into liquid salt. The rods should be in for at least 15 min before blades. Rods are removed just before blades are put in. After rods are cool, wash them in clear water to remove gunk.
Last Design Addition
Just to promote convenience and to remind us to preheat the material going into the hot salt, we welded a preheat tube to the heating jacket of the high temp pot. This assures we won't accidentally add any moisture to the hot salt.