Sciencemadness Discussion Board

Autoclave - adapt, build, buy

Oxydro - 3-2-2008 at 15:00

I need a rather large autoclave, and the prices are a little high for my taste. Therefore, I'm thinking of making one.

The basic idea is a cylinder (or other shape, but a cylinder is the strongest) made of steel plate, with elements (hot water heater) at the bottom, the appropriate controller (thermal? pressure? don't know which), gauges, safety valve etc.

I can weld the structure together, but I'm not sure about doing pressure welding, if it lets go I'm in trouble. I can always do a static test to a higher pressure before using it.

Another concern is the steel case rusting. Not sure what coating would hold up without pinholes, and stainless is expensive ( plus I don't think I can MIG weld it)

So, has anyone done this, or contemplated it? Any suggestions, warnings, etc? How about starting with a water heater?

chemrox - 3-2-2008 at 18:17

why can't you MIG weld stainless? just use the right gas and the right wire..I don't think autoclave pressure are that high ...what are you sterilizing? could you use a pressure cooker?

Magpie - 3-2-2008 at 18:54

I have given some passing thought to building an autoclave. I would use stainless steel pipe for a general purpose vessel, probably ss316 as it has increased halide corrosion resistance over ss304. It would have industrial style standard flanges on both ends (150lb or 600lb rating). I would have it constructed to my specifications as I don't have welding skills.

This could be made as complicated as one desires. It could have ports for a pressure tap and a thermowell. It could also have an agitator but that would really complicate the design. Or it could be just shaken for agitation. Heating could be by external jacket, internal coil, or simpler means.

So I suppose one should have some definite purpose(s) in mind before building because of the many design options.

The forum library has a good reference on building autoclaves. Also, for hydrostatic testing you can build your own tester as I did:

With this tester I tested as high as 430 psi (29 bar) but I could have gone higher.

[Edited on by Magpie]

Oxydro - 3-2-2008 at 19:34

I should have said, can't easily MIG it. Our welder (at the shop I work at) is set up for flux-core (no gas) right now, and I have no wire for SS. I could get it I suppose. I always associated it with TIG welding, but I guess there's no reason it has to be.

SS is also expensive and not all that readily available around here.

Autoclaves are not high pressure, this is true - only 15 to 30 pounds for most of them - I would want 60-100 so I feel safer. But a cylinder under say 30 psi, with a 18 inch diameter, is (18/2)^2*3.14 = ~254 area on each end with the end bearing 254*30= 7650 lbs pressure.

I'm sterilizing grain for bulk growing oyster mushrooms. A pressure cooker would work, that's what I'm using right now, but I want to scale up. Big pressure canners are expensive, I could build a great one for the price of buying a good one. It doesn't need to have anything fancy, timer, agitator, etc. Just some way of keeping the temp / pressure where they should be. And it should hold a lot!:D

I'm converting the shell of a water heater into a casting furnace for another project, made me think I should maybe get another one and use the tank as my pressure vessel. I know they're good for at least 100psi, probably a lot more. If I can add maybe another element for faster heat-up time, build in racks to keep my jars in order, create a locking lid and add the controller I need (or modify the existing one? how do those suckers work?)-- I have pressure switches for jet pump and compressor use which might be adaptable.