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ubermaker77 OP t1_j1g6ztk wrote

Reply to comment by keithrc2000 in Still using a 1930s pressure canner (from National Pressure Cooker Co.) that's been used by my family for 5 generations by ubermaker77

I'm not sure. If any engineers or metallurgists see this and want to weigh in I'd be interested. This is super thick cast aluminum, not anything like modern stamped metal pressure canners/cookers. But I don't know how that bears on metal fatigue.

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GodlessAristocrat t1_j1gb9ye wrote

You can take it to your local Extension office and they can check it for you.

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barefoot-warrior t1_j1h1jck wrote

Sorry if this is a dumb question but I've seen extension office mentioned multiple times and I haven't the foggiest what this is? I'm new here

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GodlessAristocrat t1_j1i4l26 wrote

Not dumb at all. /u/Andyb1000 (below) answered it.

For those not in the US, I'm not sure if there is an equivalent in the EU or other parts of the world. Maybe someone can chime in.

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frickenfantastic t1_j1ia2h8 wrote

there isn't a direct equivalent

The extension service was part of the land grant universities that were established in the US

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nolanhoff t1_j1hs956 wrote

Because it’s aluminum it will fail at some point. It isn’t ferrous, so it doesn’t have an endurance strength( Infinite life). How many stress cycles it can endure, I can’t tell you. It all depends on how they designed it.

Pressure vessels are usually required to have a factor of safety of about 6, but I’m not sure if something like this would need to adhere to that. If it did have that high factor of safety, it would last quite a long time.

For a reference point, it could be designed for 10,000 or 100,000 or 1,000,000 cycles. You’d have to ask the engineers who designed it that question.

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blueballz76 t1_j1ibhc9 wrote

It's a pressure vessel, that means it cannot be designed for infinite life, all pressure vessels eventually fail.

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frickenfantastic t1_j1iphpm wrote

For similar pressure vessels in industrial service (like 50,000 gallon tanks), we'd not let a unit like this be operated without a fitness for service test every ten years or so.

Any company that does fitness for service tests for industrial equipment could probably do the same tests (ultrasonic thickness, joint/weld testing, etc) and make a determination if the vessel is safe to keep using, but I'd expect that to be cost prohibitive.

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LeonardTimber t1_j1ikdjk wrote

Small nit pick - ‘ferrous’ just means it has iron in it and does not guarantee infinite cycle life. Cast iron or pig iron, for example, have a cycle limit.

For some reason, the inclusion of Carbon with Iron is what makes a material with infinite cycle life under a certain load, so Steels are generally the only materials with infinite cycle life at low cycle loads.

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ubermaker77 OP t1_j1irxrt wrote

Well, I can't imagine that this has been through more than 1k-2k cycles, max. My mom had it in storage for the better part of ~20 years and only used it a few times. This isn't and hasn't been used with commercial/industrial frequency, people, just 5-10 times a year. All the evidence I have supports that it's completely safe if used and maintained properly.

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SadElkBoy t1_j1iymc4 wrote

I don’t know if I would use a potential blast device without knowing it’s life. Sorry, not worth it

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jollygreengrowery t1_j1j9kad wrote

I feel like using old space heaters is bad for the same reason.

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nolanhoff t1_j1jk4ht wrote

Electric space heater?

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jollygreengrowery t1_j1jn2xf wrote

Yea the electric ones. You'll see them at yard sales for $5... the cord will have been repaired at least once and it was likely made 20-35 years ago

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nolanhoff t1_j1jn9qr wrote

Eh, other than no safety measures I don’t believe anything due to fatigue could fail, much less cause a fire.

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windoneforme t1_j1hr5a8 wrote

Cast metals are more prone to cracking than stamped. They are more brittle due to the crystalline structure that forms with the cooling of the metal.

I'd also like to point out that a modern canner would have an additional back up pressure relief device. If anything clogs the pressure regulator (but of food, rust or other corrosion for 60-80yrs of exposure to moisture ect)on this type you're in for a kitchen remodel at best, or a casket at worst.

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uslashuname t1_j1i0rj7 wrote

I was suspicious when you said it was cast aluminum and not stamped… I zoomed in to try and spot what I suspected and I think it’s pretty clear. I bet you there’s an outer shell and an inner shell, they (partially) fill the outer shell with molten aluminum then push the inner shell down to squeeze it out until what you have is s as middle layer of cast aluminum. You can see the outer and inner shell on the lip to the right of the “open” word, look for a line near the top of the rim and a line near the bottom. The inner shell is effectively perpendicular to the cut by the time it comes all the way to the outer edge of the lip, so it can appear thinner than the outer shell which may have been cut at an angle.

To see if those shells are steel is easy: are they magnetic?

It would be good if they are, you don’t want aluminum in your food and it does leech extensively especially in acidic foods.

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ubermaker77 OP t1_j1ir2ka wrote

Interesting! Yes it does have a shell apparently, but it's aluminum not steel. This is just a canner, not a pressure cooker, so there's no contact between the aluminum and our food. We don't use aluminum cookware because of the leeching you pointed out.

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