Service vs working pressure

[EHowe]

I obtained a couple of steel 72 tanks with 1971 production dates. They have current 2019 hydro stamps. I don’t see that they have ever had a + rating so fill pressure is 2250. I also have a set of LP steel 50’s produced in 2013 with a + rating that I am comfortable filling to 3000. How risky would it be to fill the older ones to a working pressure of 2475?

[tbone1004]

they passed hydro at 3750psi, their burst pressure is far higher than that. Burst test minimum is 2.25x service which is 5100psi. I think you'll be just fine at 2500, but I'd probably fill it to 3k if it were mine and wouldn't think twice about it

[captain]

I find it odd that the original hydro date does not have a +.

[EHowe]

When getting a hydro can you request a + rating?

[captain]

You can ask but will not receive. Two things would be required, 1- the original manufacture's (PST) documentation of the tanks REE, not available if it even ever existed. 2- Using the procedure described in the CFR for measure wall thickness and computing the REE from the measurements to determine wall stress. That also ain't happening. Not because it is impossible but because the average hydro shop does not have the equipment or expertise to do it.

[luis]

Are you saying that there is no + stamp next to the original manufacturing hydro date?
Are they stamped 3AA?
If they are stamped 3AA, check carefully for the original + stamp.
Without the original + stamp you are out of luck.

If they are PST, there is actually a document with the REE number, but there is an obvious typo in the document and therefore many hydro facilities will not recognize it. It is obviously a typo and the document seems to be legitimate.

Calculating the REE is not that difficult, but you need some data. Like Captain said, you need the average wall thickness among other data.

You will also need a precise internal volume for that particular cylinder. This is measured by filling the cylinder with water and measuring the weight of the water. You will be surprise in the variation in actual volumes from one steel 72 to the next. Most of them are actually around 70 cu ft at 2475 psi.

To measure the wall thickness is a lot easier than it used to be. Now you can buy ultrasound measuring devices for a little as $80.
I don’t own one yet since I had access to the ones at work (with the help of a certified technician that operated it), but I have been thinking about buying. I have a cut-off cylinder that I can use to calibrate it the ultrasound device against section of the same type of steel with a wall thickness that I can verify with a dial indicator.

Here are some ultrasound thickness measuring units:

https://smile.amazon.com/Ultrasonic-Thi ... B07FL2FRNH

https://smile.amazon.com/dp/B07QGZ94D3/ ... _lig_dp_it


https://smile.amazon.com/dp/B07FL2FRNH/ ... _lig_dp_it



Here is the document from PST with the REE number: