Failed Hydro

[rob.mwpropane]

Overexpanded by 2 PSI is nonsensical.

Since I don't understand the test, can you elaborate a little?

Thanks.

 

[James79]

Since I don't understand the test, can you elaborate a little?

Thanks.

As I understand it, for a hydro test they pump with water (for safety, since it can't compress. If a tank pops with air it goes boom, with water it just leaks) and it stretches a little (and they measure how much). When they relieve the pressure, they measure how much it relaxes back (by measuring the water that comes back out). With those, they get the elastic and plastic expansion numbers on it and that determines pass or fail. PSI is a measurement of pressure, not volume, so it doesn't compute as a expansion number.

Respectfully,

James

 

[rob.mwpropane]

Ok, so let me share my limited understanding of what a hydro shop does and maybe someone can shed some light on what I don't know. I know that they pump it with water (as someone pointed out earlier, water doesn't go boom under pressure). What I see online though is that they fill around the scuba tank with water also? I don't understand the reason for this?

Also, what exactly is the "roundout procedure" and why is it needed? I'm going to go out on a limb and say that it has something to do with the galvanic coating causing something to fail that really shouldn't. From my very limited understanding they pressurize the tank to 85%-90% of the test pressure and then bleed it off and repeat? @runsongas was nice enough to post the bulletins earlier in this thread, but I'm still trying to figure why this is needed and how exactly it's done?

I'd like to pick my tanks up tomorrow and have a generally good understanding of this so I can at least talk apples to apples with the guy. The tank has failed, there's no getting around that. I just want to gain some knowledge to "hopefully" not have to experience this again and to be able to know that they did what they were supposed to do.

 

[James79]

I believe I may have been mistaken on measuring the water inside... the measurement of expansion may be done by measuring the water level rise and fall in a water jacket around it.

Regards roundout procedure, if I get that right it's that the coating method used on those tanks can put them slightly out of round at rest. Which distorts the internal volume (reduces it). So the round out pressure puts it back into a true cylinder so they get an accurate measurement of expansion.

Of course, my advice is worth what you payed for it! lol. I could be off a little on the details, but this is my over all understanding of it.

Respectfully,

James

 

[greeniguana]

Your hydro facility sounds like most fire extinguisher places in my area. I take my beer CO2 tanks there, but they've screwed me on scuba cylinders. I have PST and worthingtons which will never see a fire extinguisher hydro place.

When you drop galvanized tanks off for hydro, you need to ask the person you give your tanks to; "Do you do 90% roundout?".

Then, look that person in the eyes. If they look at you funny, have a puzzled look, blank stare..... Walk out.

90% roundout is really just a prestretch of the tank done before actual hydro. This is the exact worthington criteria for rejection:

For hot-dip galvanized cylinders, in lieu of the 10% permanent expansion rejection criteria detailed in §180.205, cylinders are to be condemned if the elastic expansion exceeds the REE that is marked on the cylinder.

When you pick up the tank, you can ask them what measured elastic expansion (EE) was. EE and relative elastic expansion (REE) are in cubic centimeters, not PSI, so it sounds like that shop might not know what they are doing.

My galvanized tanks' EE have never even got close to their REEs.

 

[rob.mwpropane]

I believe I may have been mistaken on measuring the water inside... the measurement of expansion may be done by measuring the water level rise and fall in a water jacket around it.

Regards roundout procedure, if I get that right it's that the coating method used on those tanks can put them slightly out of round at rest. Which distorts the internal volume (reduces it). So the round out pressure puts it back into a true cylinder so they get an accurate measurement of expansion.

Of course, my advice is worth what you payed for it! lol. I could be off a little on the details, but this is my over all understanding of it.

Respectfully,

James

So when they test do they test @ 85%-90% as the paper says and then let off and test to 100%? Or are they not supposed to exceed 90% of what's stamped on the tank?

If Alabama was closer payment would be at least a round on me!

 

[rob.mwpropane]

Your hydro facility sounds like most fire extinguisher places in my area. I take my beer CO2 tanks there, but they've screwed me on scuba cylinders. I have PST and worthingtons which will never see a fire extinguisher hydro place.

When you drop galvanized tanks off for hydro, you need to ask the person you give your tanks to; "Do you do 90% roundout?".

Then, look that person in the eyes. If they look at you funny, have a puzzled look, blank stare..... Walk out.

90% roundout is really just a prestretch of the tank done before actual hydro. This is the exact worthington criteria for rejection:

For hot-dip galvanized cylinders, in lieu of the 10% permanent expansion rejection criteria detailed in §180.205, cylinders are to be condemned if the elastic expansion exceeds the REE that is marked on the cylinder.

When you pick up the tank, you can ask them what measured elastic expansion (EE) was. EE and relative elastic expansion (REE) are in cubic centimeters, not PSI, so it sounds like that shop might not know what they are doing.

My galvanized tanks' EE have never even got close to their REEs.

It is a fire hydrant facility, but it's my understanding that they take care of all the LDS. It was actually harder to get in there as they don't deal with the public. I had to setup a business account. It was easier and less expensive going through them for $25 / tank as opposed to the $50 at the LDS. (The LDS does fill / VIP but I have my own compressor).

So with the roundout do they ever exceed 90% of the stamped test pressure? I'm trying to follow you...

 

[Johnoly]

Couple of years ago when testing my tanks my hydro tester text msg me and told me the time to be at his place to watch my tanks get hydro tested. He really wanted me to see (and tell others in our club) that they have nothing to hide and it's a straight forward measuring process. You should set up an appointment with your tester and watch him test a fresh tank. You should do the same with your repair tech when they service your regulator and they'll happily show you the guts and what's good and bad inside.

Don't go and you won't know.

 

[Divin'Papaw]

Bummer! I've owned galvanized steel tanks for 15 years. At one point I owned 12 of them. Now I'm down to 4. I've never had one fail hydro. All 4 of my existing Worthington HP tanks have seen their 3rd hydro without issue. I always use dive shops that run a large volume of galvanized steel tanks through their hydro vendor. That helps me to feel comfortable that the facility is used to dealing with galvanized steel scuba cylinders. So far so good.

 

[greeniguana]

Not sure I understand question.

1 tank is pressurized to 90% of TP.
2 tank is depressurized.
3 tank is pressurized to 100% of TP
4 cubic centimeters of elastic expansion are recorded
5 tank is depressurized.

If the measuremt in step 4 is greater than REE, tank fails hydro. Unless I'm mistaken....