Catastrophic Failure of Stainless Cooking Pot 1

[AdamPrince2]

I saw a cooking pot that was made of stainless steel. It was used to cook potato soup. After cooking a restaurant owner decided to soak the pot in hot soapy water over night in the sink. The next day he found the pot literally cracked up like a banana peel! I have attached a photo. What failure mechanism would cause such a spectacular failure of a cooking pot?

 

[IRstuff]

I'm guessing it was a failure of physical security; an angry ex-employee took a hacksaw or tin snips to the pot. Or, someone took a hatchet to the pot

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[arunmrao]

A disgruntled staff, expressed his ire on the pot.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[3DDave]

The lack of particular deformation at the rolled edge rules out a hatchet, as does the lack of particular deformation at the cracks. Usually stainless is very malleable and will bend a lot before cracking. The cracks look sharp, so no hacksawing was involved.

Was it just soap?

Check this image:

 

[kingnero]

Any way you can determine the type of stainless? (because I've seen chromed steel pots being sold as stainless, however this does not look like such).
Understandinng the base material is a first step towards determining the cause of this.

Anyway, since we're all guessing, here's my $.02: chlorides in the soup/soap.

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[metengr]

This is not a typical cooking pot. It appears to be a metal liner of some sort. The orientation and appearance of several radial cracks suggests local tearing (ductile) in heavily cold drawn sheet. Either some sort of internal over pressure event when cooking or combination of temperature/pressure over stressed the liner.

 

[Compositepro]

Could it have frozen while full of water?

 

[mrfailure]

Given the suddenness and degree of cracking, I might suggest looking for stress corrosion cracking. The through-wall cracks may look straight macroscopically like in the photo, but you might see secondary branched cracks characteristic or SCC if you look closely. This is possible if chlorides were still in the pot (i.e. it was not rinsed of the soup or chloride-containing cleaner was added and not thoroughly rinsed before soapy water was added).

 

[swall]

Following up on metengr's deep drawing comment, perhaps the article had cracks all along and the soaking in the unknown agent finished them off (SCC).

 

[mrfailure]

Deep drawing would account for high residual stresses, making it susceptible to cracking from subsequent exposure to chlorides. One clue that there was high stress from drawing is how the section at the end is peeled outward, which would require high residual stress.

 

[XL83NL]

kingnero's 2 cents and metengr's comment = mrfailure's outcome. anyways, maybe the owner used a sopay water with some chlorine/bleach to 'clean the pot' after heavy use, e.g. when it has stains that werent easily removed just by rinsing and regular soap.

 

[EdStainless]

All liquid soap contain chlorides, salt is added in order to control the viscosity.
I have tested samples of dish soap that people wanted to use as assembly aids and found over 3% Cl in them.
This is more than enough for CSCC to happen.
My hunch is that the under side of rolled lip is rough, and the notches in it are where the cracks started.
If they filled the pot with hot water (185F) then CSCC is the likely cause.
It doesn't happen often in cookware because the pots either deform enough to relieve the stress of cooking warms them enough to get a bit of stress relief.


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P.E. Metallurgy, Plymouth Tube

 

I think the key here is in the forming operation, which required a very large amount of deformation to achieve the shape we see. The constant orientation of the cracks seems to support this. Possibly it was spun? Certainly the designed shape is an unfortunate one, as it asks a lot of the material.
I also would suspect SCC, but if that was the case, should we see so many cracks? Because the fluid would have escaped after the first one (unless it was inside another container).
One of my first failure investigations many years ago was on a large spun dish that had cracked before completion. I learned that the formability of 304 type stainless steels is sensitive to nickel content, and of course nickel being the most expensive ingredient in SS, will usually be in the lower end of the composition range. An intermediate anneal would have helped here, but of course that also costs. I think at the end of the day it was just a poor design, poorly executed.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Depending where in the world this pot was made it is likely a 2xx series alloy (less Ni).
And it was probably cold worked heavily (how magnetic is it?).
And I suspect a rough edge in the roll created multiple initiation locations.
I presume that it was sitting in soapy water, as well as filled with it.
If it was spun to final size the residual stresses would be compressive and not add to SCC.
But often after spin forming they are pushed though a sizing ring to remove ripples and get uniform size and roundness.
This final sizing will result in residual tensile stress.

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P.E. Metallurgy, Plymouth Tube

 

[mrfailure]

Multiple cracks under CSCC are common and do not surprise me: the high residual stress existed around the circumference, especially near the rolled edge so multiple single incident cracks can be expected (formation of a crack in such a large component does nothing to relieve the steady state stress at the other locations).

 

Crackpot designer in my professional opinion.
Sorry.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[ornerynorsk]

Having been in the restaurant biz as a sideline, I would have to say that the picture is likely an aluminum soup kettle liner, made of aluminum, not the inner cooking pot which would, in fact, be made from a 300 series stainless. You see heat shields and liners like this in a lot of restaurant equipment, and they are usually very thin. The heating elements would be on the outside of this liner, the cooking pot on the inside, and a half liter or so of water separating the 2. These would be kept at 155 to 165 deg F for many hours a day, every day. Minerals in the water + long term exposure to heat = the corrosion and cracking, IMHO.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[monkeydog]

Hmm 303 CRES with Cl in the soap and water could have caused the stress corrosion cracking.

 

[mrfailure]

The curved lip indicates that is really the stainless steel inner pot. The rolled lip at the opening allows it to be lifted out of the water.

 

[AdamPrince2]

The restaurant was in a small town run by a husband and wife in Texas. Given some time I can find the name of the place. The husband is a welder and we got to talking about metal failure. I could call and ask some details. I don't believe they have any employees that would hatchet it. It said he found it like that in the sink in the morning after soaking.

I believe it's stainless steel. I have a video of the pot.

So very high residual stresses and constant exposure to boiling salty soups and possibly bad alloy led to massive and sudden stress corrosion cracking while soaking in the sink afterwards?