can you say... burst!

[8dust]

Always a good idea to remember and thank, heartily, those members of the LDS community who indulge (put up with) our little fascination connected to vintage dive equipment...
Photo below is of a burst disk, one of the huge USD 9/16” ones that, well, burst...
Didn’t crack and fail… but friggin’ b.u.r.s.t... notice the substantial amount of missing material from the center... It took out a chunk... well, more accurate to say, put a chunk into, several chunks into really, my friend and good-natured LDS operator... as, if you are not familiar with them, those large 9/16” bolts are equipped with big, too big, vent holes on the flats of the bolt head. FYI - These vent holes are large enough to pass multiple razor-sharp shards flying at 3000psi... probably has something to do with them not being made quite that way anymore...

My friend shook it off as business as usual, as is his nature, but I’m sure it rattled him good when it blew, and I saw the bloody paper towel and the multiple penetrating wounds in his forearms... I just absolutely thank God it didn’t bite him any worse than it did.

Moral of the story... Be extra kind to your LDS man/woman… since they don’t have to put up with our eccentricities, and many of them won’t!
Show the ones who will and do, a little extra love every time you can!!! AND always, ALWAYS, wear a good pair of safety glasses... for pretty much everything that you do short of taking a poop, and maybe even then too... just to be safe...

[crimediver]

I have had a couple of experiences with a disc going and had one of the old school lead plugs let go. Not sure where it went but often wondered how it would have felt.
Reminds me of Christmas Story where Ralphie asks Santa for a scuba tank and says "Are you crazy kid? You'll shoot your eye out!"

[Scubaengineer]

The disc you shown bursting looks unusual. I test burst discs on cylinder designs and "normal " fractures usually tear resulting in a disc that looks like a toilet seat. It looks like your disc maybe wrong material. They usually do not shatter but tear.
ED

[luis]

Great observation.

I agree, all the burst discs that have seen let go are sheared around the perimeter. The inside edge of the bolt behaves as a calibrated cutter.

Modern burst disc are sold with a new bolt. It seems logical to replace the bolt in order to have a new fresh cutting edge to go with the new disc.

[8dust]

Well, I'm certainly no engineer like you fellas, but I am an art school grad...

Yall may make the connection right off, but for folks less experienced with metal and its varying array of properties and peculiarities... let me e'splain... and possibly stick my foot in my mouth for getting into a discussion of metallurgy with a couple of engineers...

So, you know how if you bend a steel coat hanger a dozen or so times, it bends easier and easier, and it then breaks pretty much right at the site of the bending... well steel is like that, it gets softer when fatigued, more or less, and when you want/need it hard again you have to heat it up and quench it.

Copper, however, works pretty much the opposite way... If you need a short piece of scrap wire and you strip a length of romex and then start bending away on a strand, what happens.... it bends a few times, then gets harder to bend and the bend moves a 1/2" or so, then another, then another, and it won't ever break like the coat hanger... shouldn't have left the cutters in the truck... Anyway, copper gets tougher, and more brittle when repeatedly fatigued. When you shape a copper bowl with a mallet, you need to keep heating it up to "release" or soften it.

All of which is to say, that the disc failure is completely my fault for waiting until after midnight to start on my projects, forgetting to replace the disc although I was sure I had, and leaving one in place that I'm sure over the course of 40 years or so had more than a few fills and stresses on it, so with each little stretch, it got more brittle, and more brittle, and more brittle, and eventually failed as it did, in flying shard fashion, rather than as you would expect a new disk placed under excessive pressure to fail... in more of a tearing or punching-out type of way...

That's my diagnosis, but then again I could be completely wrong... I'm definitely not the smartest guy in the room. Either way, it did what it did, which was multo-bad, and I'm lucky to have not hurt my friend as a result of my mistake. All the more reason, PSI Inspector or not, to work on these projects on Sunday afternoons and NOT at 1:30 am on a Thursday, AND to be super kind and appreciative of your LDS who tolerates you and your "old junk."

[antique diver]

Nice explanation, Freddo!

[swimjim]

Being from Tennessee and all, I'm sure working stuff like copper tubing it's just in your blood Fred. Heck, I remember driving I-40 East of Knoxville one day and I swear I could smell that sour mash coming down the mountain!

[luis]

Hi Fred
Well, there are a few technical and terminology errors...

Obviously, your general observations are correct... I will never argue against a physical observation, but your terminology and explanation are not technically correct. Technical terms are often not used with their precise meaning. As most of you know, English is not my first language, but when it comes to technical communication, I try to be precise (key word “try”).

Copper is a very ductile material and doesn't tend to work harden like steel does. That is why the wire you are referring to flexes so easily and it doesn’t tend to fracture (or crack). Work hardening tends to make a material more brittle and prone to fracture (like the coat hanger). Note that I am using relative qualifiers like "tends to". I don't know that there are any absolutes in metallurgy.

Steel doesn’t get softer when it fatigues. Working steel actually work hardens it, which increases it yield strength, but it makes it more brittle and prone to cracking/ fracturing.

A brittle material is one where the yield strength is close to the ultimate strength.

When you heat steel (to red hot) and let it cool down slowly (not quenching) it tends to anneal it, relieving the work hardening effect.

In any case, there are a number of explanations of why the disc failed the way it did, fatigue would not be in the top of my list, but I am not ruling it out.

BTW, I am not a metallurgist or material science expert in any way. I just have a working knowledge of some materials.

I was going to make a guess and try to explain the disc behavior, but I think I am going to wait until next week. On Monday I should be able to talk to one of my officemates, who actually has some credentials in welding and material sciences. He is our material go to guy (he doesn’t like to call himself an expert either).

And while I am at it, I will also stay clear from making any explanations about art.
Just kidding…

[luis]

I did talk to my officemate and showed him the picture.

He pretty much ruled out a true fatigue failure. Keep in mind that this are not reversing load cycles. The pressure load only cycle from zero to a positive. The load never reverses. Fatigue failure can occur without having reversing cycles, but the fatigue curve (S-N curve, Stress versus Number of cycles) is different (many more cycles needed).

Also the number of cycles is very low for a true fatigue failure. Even if you filled it and emptied every day for years, the cycles are very low for a fatigue failure when the stresses are in the elastic region.

The coat hanger example we all know about is not exactly a elastic stress fatigue failure (elastic stress range). The coat hanger is bent into a high stress plastic permanent deformation condition, which work hardens the bending spot.

When the stresses on a metal piece are below the yield strength, the part deforms elastically and will return to its original shape when the load/ stress is removed. This called elastic deformation. When the load causes stresses that exceeds the yield strength, the piece will have some permanent deformation. This is called plastic deformation.

In the case of the coat hanger the plastic deformation is extremely high if it bent into a very tight radius. It doesn’t take very many cycles of this extremely high stresses to initiate a fracture.

I hope my explanations are clear.

In any case, I am still puzzled (and to a lesser degree so is my office mate). If you still have the disc, I would like to examine it. If you could mail it to me, I would like to take a look at it.

I would also like to see the bolt. Is the inside edge rounded?

We are both thinking there might have been a flaw toward the center of the disc were the ruptured started. My thought is that corrosion might have caused some pitting that created a crack starter, but I am not even sure about that possibility.

Do you know at what pressure it let go?