Catastrophic Failure of Stainless Cooking Pot
Catastrophic Failure of Stainless Cooking Pot
(OP)
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?





RE: Catastrophic Failure of Stainless Cooking Pot
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RE: Catastrophic Failure of Stainless Cooking Pot
"Even,if you are a minority of one, truth is the truth."
Mahatma Gandhi.
RE: Catastrophic Failure of Stainless Cooking Pot
Was it just soap?
Check this image:[img https://static.thefabricator.com/a/die-science-sta...]
RE: Catastrophic Failure of Stainless Cooking Pot
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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RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
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
RE: Catastrophic Failure of Stainless Cooking Pot
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."
RE: Catastrophic Failure of Stainless Cooking Pot
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
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
Sorry.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Catastrophic Failure of Stainless Cooking Pot
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.
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
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?
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
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RE: Catastrophic Failure of Stainless Cooking Pot
A nice brain teaser, thanks for posting.
The discussion has gone around forming operations and SCC. But seriously, where was the tensile stress that caused SCC? Residual stresses at the time of forming has caused CSCC...wow!
Did anybody ask how old was the cooking pot?
If possible, take a sample and carry out metallography. Then the world would know the answer.
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Catastrophic Failure of Stainless Cooking Pot
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Catastrophic Failure of Stainless Cooking Pot
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.
RE: Catastrophic Failure of Stainless Cooking Pot
1. It is an austenitic SS (because of its thickness and the way it is formed)
2. The quality of the SS, specially with respect to Carbon content, is not maintained.
Don't you think sensitization is more likely the cause of failure than SCC?
@ironic metallurgist: thanks for the input on residual stress.
RE: Catastrophic Failure of Stainless Cooking Pot
My bet is on SCC. Plenty of residual stresses, plenty of chloride, plenty of oxygen.
Makes me look at my stainless pressure cooker a little warily to be sure..
Nathan Brink
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
Many folks confuse sensitization with stress corrosion cracking.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Catastrophic Failure of Stainless Cooking Pot
Actually in a part that is heavily formed higher C can be good since it is an austenite stabilizer.
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P.E. Metallurgy, Plymouth Tube
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
I recall arguing with design and manufacturing engineers who were sure that austenitic SS weld overlay could not be PWHT before machining or it would be certain to crack in cold, fresh water. Sensitization was always given as the reason for making manufacturing of these components more onerous and costly.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Catastrophic Failure of Stainless Cooking Pot
The curious thing is that there are environment that will cause cracking in all known alloys (even gold will crack in HF).
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P.E. Metallurgy, Plymouth Tube
RE: Catastrophic Failure of Stainless Cooking Pot
Would we also expect the cracking to happen when the object was sitting around in a presumably cold soap solution?
Agree that the conditions for chloride SCC are all there- heat, stress, oxygen, chloride and stagnant conditions. But those conditions are encountered in all cookware- perhaps the exposure duration of this component, being used in a restaurant, was long enough for pits to start- from what I've read, pit initiation is necessary before Cl SCC can start.
Better photographs would be needed for the people (unlike me!) competent in failure analysis to do more than just guess about it. There's a burr on one edge of one of the cracks that makes it look rather like a sawcut- that and the regularity of the distance between the cracks looks a little suspicious. I'm sure the owner could tell the difference between a sawcut and a crack, but it's impossible to tell from this photo.
RE: Catastrophic Failure of Stainless Cooking Pot
Mu hunch is that the rim is usually dry, in use any liquid there would evaporate. But this was being soaked and there could have been fluid there. Combined with the hot water in a restaurant being 185F I could see this finally happening.
I have never seen a pot crack while cooking, but while soaking and cleaning it isn't unheard of.
Yes you do need active corrosion for SCC to occur, but the pits can be microscopic so that there is no apparent corrosion.
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P.E. Metallurgy, Plymouth Tube
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
RE: Catastrophic Failure of Stainless Cooking Pot
SCC will most definitely take place in 316SS when there is high heat stress (as in cooking on a high temperature burner, with little or no water left in pot, or steam with exposure to chloride containing water as a quencher/coolant. I have seen boiler sample cooler fail within a period of 2-3 days when subjected 316L stainless steel tubing coils to raw hard water containing 200-300 ppm chloride.
Generally, this was a failure waiting for a place to happen.
I guess time ran out, or actually the soup was going to run out?
Is this why most pressure cookers are made from Aluminum alloy?
RE: Catastrophic Failure of Stainless Cooking Pot
Was thermal shock involved, i.e. hot stove to relatively cool hot water?
Would it have happened if the pot had been left to cool on the stove?
[edit]I've had a quick read and it would seem to me that it's time had come, and there was no specific event that caused it to fail. Chemical inclusions seem to promote the failure, but the actual time of failure is unpredictable. Is this correct?[/edit]