Invisible Fractures in Glass

appling a dye should show any cracks. i believe a marker pen will do the trick.

Use black light. Set it so it shines down through the the edge at the top. Any cracks and imperfections will show up.

I have heard that the the type of glass used for Pyrex changed about 20 years ago.

The date of manufacture of your potential planter may therefore be important.

Pyrex = borosilicate (vs soda-lime) glass. It has been around for a long time. If there have been recent changes, some specifics would be nice.

Once upon a time, all Pyrex glassware was made from borosilicate glass. Since 1998 Pyrex consumer products have been made from tempered soda-lime glass. The laboratory glassware is still borosilicate glass, however.

http://en.wikipedia.org/wiki/Pyrex

I had to discard a one-pint Pyrex measuring cup purchased in the late 1940's because it shed little glass shards in the microwave. I have had no such problem with its 2001 replacement, presumably made from tempered soda glass. I suppose the science of glassmaking has advanced somewhat in the course of time.

Welcome to CR4.

Replacement might be more viable than diagnosis on this occasion.

any type of glass will crack if you subject it to rapid temperature changes. i think u should replace your caraffe immediately before the inevitabe happens. do not rinse it while it's hot.

Passingtongreen, I'm with you. I didn't ask the question because I cannot afford to replace the carafe. I asked it because I am puzzled and I want to know if glass, under heat and pressure, can form a crack that is wide enough to let out liquid, and then seemingly "heal" when cooled, so the crack cannot be found. Maybe I just will write a thesis...

Thanks, everyone for your comments.

GA

And if it is actually Pyrex - it's "soft" so will 'fall apart' more than 'shatter explosively' - but be cautious, a lot of those things are regular glass just very thin and annealed to cope with the mild thermal 'shock' of room temperature to 100⁰C

Gloves, eye protection, during playing.

great answer! I particularly enjoyed the "write a thesis" part...

I was just cleaning a french press the other day and it had a quarter size piece pop out of the side. I had never leaked but the way it broke was very odd. I pushed the plunger down with hot water in it and it fell apart.

Just to be clear you guys are talking about these;

Yes?

If so, the origin is a Pyrex laboratory beaker and gauze.

It is not a 'pressure vessel' and many tend to 'plunge' with excessive force, specially when cleaning.

Obviously it should be hand washed - like you best lead crystal - as it is 'soft' compared to regular glass.

And as it is soft, any small handling mistake, like a tap on the bench or sink, will cause a small flaw (fracture) which will grow with thermal or physical stress. Sometimes it runs around the entire bottom, sometimes forms it's own circle, sometimes is a spiral line mid way up.

It obviously grows faster, if instead of using a bit more than the weight of your hand - which the coffee also prefers, after sitting for 3 to 4 minutes* - for the 'slow 30 second plunge'.

But as said above, these things are now mass market and not necessarily Pyrex.

*^{_{Not that I, a mere male would presume to tell you ladies how to make coffee}}

Yes that a french press. I had been using it for weeks. It was my girlfriends and I was cleaning up from making her coffee. It was always hand washed and no excessive force.

The piece came out of the middle of the side. It was a going away gift from a close friend of hers. I felt worse than she did about it. I have washed my hand blown wine glasses for years and never seen anything like it.

Dear engineerswife:

It looks that used up trapped coffee comes out when steam comes in contact and it can come from top to bottom. Hot steam under pressure can release the trapped old coffee easily by loosening it from solid state and making it liquid after dissolving it in steam. Time delay is just to get enough hot water also trapped at the same place.

This does not mean there is some crack. This only means there is some space between glass and metal where some coffee gets trapped while poring, cleaning etc.

Dip the metal in hot water in reverse way and you can see the color coming out.

I think your engineering husband is right and in some way you are also good observer and only that you are unable to link information to the source properly.

In fact it is a cleaning problem. If you clean it by ultrasonic then on next coffee making this magic show will go away for sure. More dirty pot means more magical appearance. Just you are unable to spot the dirty area.

WHAT! (where is Sue & and the umbrage button, when I need her?)

HURRUMPH!!!!

(sue's proxy, to keep 34point5 happy...)

Hi. That's what my husband thought, too, that there might be some old coffee trapped, but since I take the carafe out and wash and dry both the glass carafe and the frame separately, then dry them, I don't think it is possible.

Yeah tap it "hard-ish" with the edge of a soft wooden spoon, and if it's whole, it will "ring" and if it's cracked.. it will give a flat note.

I had one get a knock and go the same way with a circumfrential crack that went around body of it, along a change of section.

If it's cracked... dump it.

Wrap a tissue or blotting paper around the carafe and help it with a paper tape from unwrap. Pour coffee near fill and keep in a micro oven, preferably on a piece of tissue. Heat it with care with several intervals, every time inspect for leak. Take care such that the heating time is not too long and boil the content to spill over. Hope this might expand the glass (not because of microwave on glass but on content) and opens the crack. If you are Lucky, the spot and extend also could be visible. Good luck...

Heat it in the microwave??? I would check before hand that there are no metal parts!! It is about 6 months until 4th of July, and too early for fireworks.

Bill

Dear engineerswife, Welcome to CR4. If it is a crack whether visible or invisible on Pyrex,

you would have lost it long back. You see so many inputs are coming from our expert team in CR 4 Group. Good Luck

P.Rangasamy

GA

My thoughts exactly.

Ah...

Until 1905, professors of physical sciences around the world could not imagine that measuring sticks would change length, or that clocks would change speed.

Thank you! What a wonderful analysis. That is the sort of thing I had envisioned, but could not put into words. I will save the carafe and continue to try to find the flaw, but meanwhile, I am taking everyone's good advice and buying a replacement on the Bodum website.

How much does a new coffee press (or cafetiere) cost?

My sister-in-law was using one at work and although it looked in good condition, it broke and badly scalded her legs. If these things break they will tend to do it when they are hot and full.

Is it worth it? I tend to be careful with my money when it comes to buying replacements, using things until they are "risky". But I wouldn't risk using a glass container of hot liquid if I suspected there may be a hairline crack in it, even if I couldn't find it.

See post #11

No kidding! I believe you have answered my question, and I will try to verify it by testing the beaker in a container of water. I don't expect to have much luck, because as you said, I will need to simulate the use pressure, but without using hot water, and heat is a factor as well. But it is worth a try. If I succeed in producing bubbles from a leak, I will let you know. Either way, thanks!

Please stay safe when you perform this test. We estimate the actual use pressure. In your case it should be less than 1 atm or 14.7 psi. We obtain a lid for the beaker and attach it to the beaker. Silicone sealant is good for this. Through a hole in the lid, we attach a piece of tubing and pressurize the beaker with compressed air using a pressure regulator. When the pressure reaches the test pressure, we immerse the beaker in water and look for the bubble stream. If you are careless and exceed a critical pressure, the beaker will explode and glass fragments will fly everywhere, so use caution, especially since you expect a defect.

Viscosity relation water/air is only 50!

Density relation is near 800.

With very small leaks there are no bubbles as very small bubbles rapidly dissolve in water.

The pressure inside the bubble is raising with 1/r with r= radius. So there is pressure enhanced dissolution of air in water.

Only if leakage rate is above dissolution rate there will be a bubble seen.

In vacuum technology it is well known that the bubble test is working only with coarse leaks.

RHABE

You are correct. However, op is inquiring about a leak large enough to have coffee seep through with a small pressure differential. This is a large enough leak to easily detect and locate as I described. Using pressurized gas and fluorocarbon liquid we are able (under ideal conditions) to locate leaks as small as 1e-10 atm cc He/sec. This is on the sensitive side of mass spectrometer capability.

I'm curious, because it seems you work with teeny tiny leaks, I was taught early on that "air tight" does not mean "water tight", but "water tight" does imply "air tight", and the courses in chemistry learning about molecular sizes seemed to confirm that. Have you ever run across an example of such?

Lots of examples. The important point here is that when we talk about tiny leaks, we are usually thinking water vapor. The water vapor molecule is the smallest molecule one normally encounters in air. So if a connection is water vapor tight, it won't leak liquid or air.

Hi RHABE; you wrote; "In vacuum technology it is well known that the bubble test is working only with coarse leaks"

Wouldn't a vacuum tend to close such a leak as described here?

I don't know about invisable fractures in glass. However, I've got one of those French presses and I always put it in the sink before pressing. We've had a few failures and a hot mess to clean up. Using it in the sink solves the problem.

Throw French Press into air....if it shatters when it hits floor.....it was cracked.....if it just cracks....then it was OK.

Welcome to the forum Engineers wife. I notice you are carefully reading our suggestions and responding to them.

Looking at the original post, it seems that you are looking to prove to your husband that you are not 'nuts' by getting us to show there can be an invisible leak in the carafe.

This is one of those cases where both can be true. There may be an invisible leak, but you may still be nuts. We really don't know you well enough to say.

Calling yourself 'Engineers Wife' suggests you have an identity problem for a start.

Just kidding

Psychotherapists Husband

First, among my many problems, my identity is not high on the list. Second, I admit I may well be both correct as to the cracked carafe, and cracked myself. Thank you for the free session and the clarification of my logical conundrum. In future I will call myself Competent Individual.

Dear Competent Individual (GA for that)

Thinking on Weldermans' test using air;

I'm thinking you could try covering the plunger with plastic wrap and using a little Vaseline (petroleum jelly) as a lubricant, making it a 'piston' to pressurize the air in the beaker.

If this was done in a sink of hot water, full to say an inch less then beaker height (and perhaps made hotter by addition of some boiled) it might replicate both heat and pressure.

I.e. hold the beaker submerged for a minute or so to let it heat, then "plunge" (cautiously) looking for bubbles.

Obviously use protection for both glass and scalding - should it catastrophically fail.

And don't forget the video for Doctor Professor and associated .......s above

I notice that there seem to be quite a few participants from Guru.

I find that interesting, I have driven past Guru many times, but not thus far had opportunity to visit.

I currently reside in Melbourne, but drive to Townsville every couple of years - I grew up there and still have quite a few friends there.

Is Guru still a mosquito farm, as my Father used to refer to it?

No. But you're already 10% into being be sent there.

What I say?

What I say?

I propose to use photoelasticity effect! to find crack position, the frange will become black near violet zone Best Regards

You could hold it, empty, upside down under water. It need only be a centimeter deeper than the bodum. change the temp of the water (say, by pouring a kettle of boiling water over it and see if bubbles come out.

Here's an idea. Notice the plunger gets harder to press. this isn't causing pressure, it is caused by something. What is causing the plunger to get harder to press? Is the glass deforming in some way rather than expanding evenly all round? I can see how a sealed crack in a round beaker would be a leaking crack at the sharp end of an oval beaker, but how does the beaker get to be oval? I something wicking away the heat from one area?

"Is the glass deforming in some way rather than expanding evenly all round?"

If that were the case then the glass would almost certainly brake when it got hot.

So far I think the suggestion by Rixter in post #25 and the guests in post #51 to use photoelasticity is by far the safest and most elegant solution to date.

You will however need a couple of polarizing filters and some imaginative positioning to create a setup similar to that shown in the image below.

However, it wouldn't be too difficult and would almost certainly show the lines of stress that would be present around a flaw that was opening with an increase in pressure and temperature in a similar way to the image below.

It would also be a darn side safer than adding hot water and pressure to a container that is suspected of having a flaw.

PS: Thanks to Wikipedia for the images.

Thank you for your suggestion, but this is way beyond my abilities. That's why I asked you engineers for your opinions.

If you have an old pair (alternatively pick up a cheap pair from the local service station or chemist) of polarizing sun glasses and a flash light you have all you need.

What you do is pop one lenses out of the frame and then tape it to the flashlight so you have a polarized light source. You then use this to backlight the area in question while viewing it through the lens that's still in the frame. By rotating the light source and object being viewed you will get rainbow like patterns that will reveal the lines of stress that would almost certainly be present around a flaw like the one that is suspected of being present.

It would be a bit fiddly and cost a few dollars but it would give you results that you could be used to show your other half that there was indeed something very much amok with the coffee maker.

Then again, if you are going to replace the coffee maker it's primarily an academic exercise that will add extra cost.

"It would also be a darn side safer than adding hot water and pressure to a container that is suspected of having a flaw"

Ok - I'll bite.

1. The vessel has been routinely subjected to hot water and pressure - so what is so perilous in 'duplicating the conditions' in a controlled and aware manner?

2. What level of certainty is there in the experimenter first learning the polarizing art, then applying it successfully enough to guarantee the detection of a fault, in absence of the heat and pressure it 'apparently requires' to manifest?

G'day 34point5

"so what is so perilous in 'duplicating the conditions' in a controlled and aware manner?"

Fractures and faults like the one that is suspected of being present have a nasty habit of slowly propagating until without warning they fail catastrophically. Unfortunately it's very difficult to predict when such a catastrophic failure is going to occur so every time you pressurize the container with hot water there is a risk of catastrophic failure that could have dire consequences.

A case in point were the explosive decompression and breakup of the DeHavilland Comet aircraft during the early days of jet travel.

"What level of certainty is there in the experimenter first learning the polarizing art, then applying it successfully enough to guarantee the detection of a fault, in absence of the heat and pressure it 'apparently requires' to manifest?"

That's a good point and pictures are worth a thousand words so I decided to have a paly and see what could be achieved and how difficult it was to do.

What I did was to tape and old CD cover to the LCD screen on my computer. LCD screens use a polarized light source so you don't need to mess about with sticking a lens over a torch if you have and LCD screen, all you need to is get a blank white image on the screen.

I then viewed the CD cover through a polarizing filter that I rotated to achieve the maximum contrast and recorded the images on my mobile phone.

Here are the results.

Subsequent close inspection of the cover revealed a small difficult to see crack that radiated from the upper left corner downwards parallel to the edge. It also showed a small inclusion (bubble) near the bottom edge where the colours appear to be radiating from.

So, considering how easy it was to do and how dramatic the results were, I would hazard to say that with a little experimentation any flaw like the one described would show up like a neon sign even without the added heat and pressure.

I like your sig line

Surely if there was a crack and hot coffee had passed through there would be some residue left behind which would be visible, similar to putting a dye though it. Chances are this residue would infact propageate the crack further upon cooling and contraction resulting in failure.