×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Catastrophic Failure of Stainless Cooking Pot

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

A disgruntled staff, expressed his ire on the pot.

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

Mahatma Gandhi.

RE: Catastrophic Failure of Stainless Cooking Pot

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:[img https://static.thefabricator.com/a/die-science-sta...]

RE: Catastrophic Failure of Stainless Cooking Pot

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.

---
http://be.linkedin.com/in/fusionpoint

RE: Catastrophic Failure of Stainless Cooking Pot

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.

RE: Catastrophic Failure of Stainless Cooking Pot

Could it have frozen while full of water?

RE: Catastrophic Failure of Stainless Cooking Pot

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).

RE: Catastrophic Failure of Stainless Cooking Pot

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).

RE: Catastrophic Failure of Stainless Cooking Pot

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.

RE: Catastrophic Failure of Stainless Cooking Pot

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.

RE: Catastrophic Failure of Stainless Cooking Pot

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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Catastrophic Failure of Stainless Cooking Pot

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."

RE: Catastrophic Failure of Stainless Cooking Pot

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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Catastrophic Failure of Stainless Cooking Pot

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).

RE: Catastrophic Failure of Stainless Cooking Pot

Crackpot designer in my professional opinion.
Sorry.

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

RE: Catastrophic Failure of Stainless Cooking Pot

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.

RE: Catastrophic Failure of Stainless Cooking Pot

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

RE: Catastrophic Failure of Stainless Cooking Pot

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.

RE: Catastrophic Failure of Stainless Cooking Pot

(OP)
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?

RE: Catastrophic Failure of Stainless Cooking Pot

(OP)
The place was located in Oldham, County Texas.

RE: Catastrophic Failure of Stainless Cooking Pot

(OP)
The restaurant name is:
Twisted Tulip
1208 W Main St, Vega, TX 79092
Phone: (806) 340-4245

RE: Catastrophic Failure of Stainless Cooking Pot

AdamPrince2

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

It does not take much stress. I have the example of an oven used in a pharmaceutical process made from flat 304 sheet where the cleaning agent used contained chlorides and was not thoroughly rinsed. That cracked cracked completely throughout.

RE: Catastrophic Failure of Stainless Cooking Pot

Quote (Dhurjati Sen)

Residual stresses at the time of forming has caused CSCC...wow!
Yes, and the magnitude in this case is more than sufficient to provide one of the three prerequisite conditions for SCC.

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

RE: Catastrophic Failure of Stainless Cooking Pot

p.s., at the right (i.e. wrong) temperature and with a susceptible austenitic stainless steel, chloride SCC has been observed with Cl- concentration in the ppm range.

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

RE: Catastrophic Failure of Stainless Cooking Pot

Mrfailure, at second glance, I believe you are correct. The sheen on the outside of the pot does look much more like stainless than aluminum. The rolled lip could be on both the inner pot or the liner, but the liner is generally not intended to be removed, at least not in normal use. Interesting failure to say the least!


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

For this particular cooking pot, two things are assumed:

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

I would assume such a pot would be cold drawn from annealled sheet. Why would it sensitize?


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

SCC in austenitic steels is not dependent on carbon content and happens with the right exposure in low-carbon versions of stainless as well.

RE: Catastrophic Failure of Stainless Cooking Pot

mrfailure,
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

They confuse the two because in many environments sensitized material is more susceptible to SCC.
Actually in a part that is heavily formed higher C can be good since it is an austenite stabilizer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Catastrophic Failure of Stainless Cooking Pot

For metallurgists stress corrosion cracking (SCC) is such a broad term to define cracking related to three conditions (environment, susceptible material and tensile stress), which must be present simultaneously. You have subsets of SCC, like intergranular stress corrosion cracking (IGSCC) because of sensitization, you also have transgranular stress corrosion cracking (TGSCC) associated with chloride exposure, and hydrogen related and even sulfur related, which can result in SCC (transgranular or intergranular) or SSCC, respectively.

RE: Catastrophic Failure of Stainless Cooking Pot

My theory about sensitization is that it is the only thing many non-metallurgical engineers retain from their 2nd year material science course, and so it perennially arises when discussing anything to do with stainless steel.
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 bigger name is EAC (environmentally assisted cracking).
The curious thing is that there are environment that will cause cracking in all known alloys (even gold will crack in HF).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Catastrophic Failure of Stainless Cooking Pot

Would we really expect a component with residual stress from deep drawing to have cracks ONLY in the axial and none in the radial direction? And no cracks on the rolled lip either, except through the lip?

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

Yes we would expect cracking that that direction, because the stresses are much higher in the hoop than in longitudinal.
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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Catastrophic Failure of Stainless Cooking Pot

Typical SCC often occurred on deep-drawn brass and 3xx SS! critical temperature > 70 degree C.

RE: Catastrophic Failure of Stainless Cooking Pot

It’s SCC failure where the strees comes mainly as residual from the fabrication (and use, of course) due to a deep drawing deffect like wrinkles or microscopical scratches. Thermal cycles in cooking, chlorides in the food and soap contrbuted to the mechanism.



RE: Catastrophic Failure of Stainless Cooking Pot

It appears to be case closed, based on the reports of high residual stress from deep drawing, and propagated cracks appearing to run parallel to axis, not hoop.
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.

hourglass

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

I'm totally ignorant about SCC. I'm going to Google it now, but...

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]

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close