Tank Question..

[Superlyte27]

Guys:

Did I read somewhere that there was an issue getting PST tanks to pass hydro? Was this HP or LP tanks? Anyone know the scoop?

[Walter Pickel]

Never had an issue with mine

[Sludge]

Was this HP or LP tanks?

Neither. It's the E-Series.

The E-Series is simply a LP cylinder with different numbers stamped on it. But the problem is, they are still hydro tested to 5/3 working pressure. So instead of being tested at 4000psi they're tested at 5700psi, where they're much more likely to fail.

If I have some of these numbers wrong, someone correct me. But that's the gist of it.

[JS1scuba]

Rus,

The E series is not the same cylinder as the LP cylinder.

PST made three series of cylinders prior to 2005.

The LP Series was a service pressure of 2400 psi plus a 10% over fill to get the rated volume. These would get a 5/3rds working pressure hydro test.

LP-45, LP-80, LP-95, LP-104, LP-120

The MP Series was a servide pressure of 3300 psi plus a 10% overfill to get the rated volume. This would get a 5/3rd working pressure hydro test.

MP-72

Then the HP Series (also known as Genesis series) was introduced in 1988 and was the first exemption series. This had a 3500 psi working pressure and no overfil. It would get a hydro at 3 / halfs working pressure or 5250 psi. These used the 7/8 14 small neck thread and were required to have a 300 bar din outlet valve.

HP-65, HP-80, HP-100, HP-120

All of the above worked well for many years. However ...... around 2002 Thermo introduced the Convertible Pro Valve and wanted to get big sales out of it. Thermo was heavily involved with CGA advisory panels, NFPA advisory panels etc and carefully looked at the Valve requirements for scuba. If a cylinder had a working pressure of less than 3450 psi it could use a "K" or "Yoke" Style valve. But if it was 3500 psi or more it was required to have a 300 bar din valve. .......... Since Thermo wanted to sell a lot of valves it was important to get tanks that were rated at less than 3500 psi ....... welcome 3442.

BTW this applied to PST, Faber, Heiser etc. (Faber sold the most) Worthington was not in the scuba cylinder market then.

For the HP series this would just mean changing the neck size from the smaller 7/8 14 thread to the standard 3/4 thread and slightly changing the height. That made the E series for PST for the 7.25" cylinders. For the larger 8" diameter cylinders they would need to make complete new engineering drawings, get new DOT testing etc. so that this whole new series of cylinders would meet DOT requirements. (Faber too)

Now the E series is both the 7.25" and the 8"

In 8" you have

E8-119 (similar in size to LP 95)
E8-130 (similar in size to LP104)
E8-149 (similar in size to LP 121)

Here is a tank chart from our website that pretty much has all the cylinders on it. http://www.tdl.divebiz.net/pub/tanks.html


The reason scuba cylinders fail hydro from time to time is because they have lost their elasticity. The biggest way a cylinder will lose its elasticity is to constantly over-fill the cylinder beyond it's working pressure AND leave it full. The "sustained load" is what wrecks the cylinder. I'm not a metalurgist so i dont know the exacty reason why it loses its elasticity but its like bungee-- stretch it long enough and keep it under tension and sooner or later it does not come back.

.... High Pressure steel cylinders tend to fail more often than Low Pressure industrial cylinders. (we have some we have tested as old as 1915) I've seen PST and Worthington's fail on first hydro. And fail badly (in the test range) when I ask the owners about overfilling and HOW long the cylinders sit between use - invariably they are filled fat and then sit for a month or more before use. Or they are filled fat daily and just generally abused.

Scuba cylinders are like car tires. They need to be replaced every once in a while. I know it sucks when a cylinder fails hydro but it is just part of the game. This year alone I had 5 of my own cylinders fail hydro. I think they served me well over the years. 3 were aluminum, 2 were steel.

This may have been a longer reply than you were looking for but .... what the heck. It's good info.


Cheers
JDS

[Sludge]

Jo,

I was told, off the record by someone at PST, that the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

It was off the record so I can give no citation.

[JS1scuba]

Jo,

I was told, off the record by someone at PST, that the LP and HP used different steel alloys, and that the 3442 E-Series was the same alloy they had been using on the LPs, so the E-Series was for all intents a HP with a 3/4 neck.

It was off the record so I can give no citation.

It most probably was the same alloy but the wall thickness is different. It may not be a lot thicker (like the MP cylinders) but it is different. I've had a chance to view a lot of the Faber specs, engineering drawings etc (I was big distributor for a few years) and each and every cylinder goes through a lot to get that spec approved for manufacturing. Remember these are big bombs if not made correctly.

Cheers
JDS

[cavemark]

There is a unique procedure for hydrotesting some PST tanks the if not followed will result in a higher failure rate.

[gasdiver]

I'm not a metalurgist so i dont know the exacty reason why it loses its elasticity but its like bungee-- stretch it long enough and keep it under tension and sooner or later it does not come back.

It's called work hardening or strain hardening. If you have ever tried to break a coat hanger by bending/twisting it, you've seen work hardening in action. After bending the coat hanger a few times it starts to bend at a different place because the material in the first bend area got stronger. After a while, it will break because the material is no longer ductile. As the steel tank becomes harder, it looses it ductility and this is what the hydrostatic test is measuring. During a hydro, you fill the cylinder up with water and then compress a very small air space to say 5/3 of the tanks working pressure, the hydro is measuring how much volume is displaced (tank expansion). When the pressure is released the final volume is compared to the original volume. The final volume must be within a small percentage of the original volume or the tank fails. In other words, if the tank expands and does not come back to its original size, it has work hardened. Keep doing this to a tank and it gets progressively worse until, kaboom...

[go62onair]

Guys:

Did I read somewhere that there was an issue getting PST tanks to pass hydro? Was this HP or LP tanks? Anyone know the scoop?

There is no issue if people doing hydro know what they are doing and follow the proper procedure. Ask first. See below.

PST Technical Bulletin D101 Retesting DOT-E9791 or TC-SU4349-241 Advanced Technology Cylinders Revised 3/20/2000
High pressure steel SCUBA cylinders manufactured by PST must be reinspected and retested at least every five years in accordance with the Code of federal Regulations Title 49 CFR 173.34 (US) or CSA B339 (Canada).
PST high pressure (3,500 psi.) cylinders must be retested in accordance with DOT-E9791 or TC-SU4349 and have special test requirements based on their design and the DOT/TC requirements. This bulletin provides the necessary information.
1. The retester must have a current copy either DOT-E9791 or TC-SU4349.
2. Use a test adapter that matches the MS 16142(SH) port in the cylinder. Hydrotest Products Part No. 100-58 with o-ring is a suitable adapter. Adapters designed for 4,500 psi. Fireman's cylinders may not seal properly and should not be used.
3. The test pressure is 5,250 psi. DOT requires a test pressure of 3/2 times service pressure for all newer designs.
4. The wall calculations of CGA-C6 are not applicable to these high-strength steel cylinders. For the purposes of inspection criteria, the minimum wall for a new cylinder is 0.179 inch, the estimated actual wall at time of manufacture is 0.195 inch and the minimum wall in service is 0.172 inch.
5. Almost all PST high pressure SCUBA cylinders are hot-dip galvanized for protection from corrosion. Specific procedures must be followed for cylinder preparation and retest checks to obtain accurate results in retesting hot-dip galvanized cylinders. These are described in PST Bulletin D100, Procedures for Hydrostatic Retesting for Hot Dip Galvanized Scuba Cylinders.
Following these procedures will assure an accurate retest for PST SCUBA cylinders. If you experience any difficulty in obtaining acceptable readings, please contact PST SCUBA customer service.
These bulletins are provided free to all retesters approved by the US DOT or Transport Canada.

PST Technical Bulletin D100 Procedures for Hydrostatic Retesting of Hot Dip Galvanized Scuba Cylinders Revised 3/20/2000
Steel SCUBA cylinders manufactured by PST must be reinspected and retested at least every five years in accordance with the Code of federal Regulations Title 49 CFR 173.34 (US) or CSA B339 (Canada).
This bulletin describes procedures that must be performed prior to retesting each cylinder. The cylinder must be prepared and test system checked in order to obtain accurate results in the hydrostatic expansion retest of galvanized steel cylinders. All PST AquaAire SCUBA cylinders and older PST SCUBA cylinders made starting in 1952 are protected from corrosion by a hot dip galvanized coating. This hot dip galvanized coating may affect the readings from the hydrostatic test, therefore failure to prepare the cylinder and perform the test system check in accordance with this procedure may result in rejection of perfectly acceptable cylinders.
Cylinder Preparation Procedure:
1. Remove the plastic boot.
2. Remove any crusty white corrosion deposits. Crusty deposits are most likely to form inside the removable plastic boot if the owner has not routinely rinsed saltwater residue from this area.
3. Do not use aggressive acidic or caustic metal cleaners on the galvanized surface. The mottled gray-white appearance of used galvanized cylinders is normal.
Test System Check Procedure:
1. Visually inspect the cylinder, fill it with water and place it in the water jacket, as is your normal practice for any cylinder.
2. Zero the burette or expansion measuring system and pressurize the cylinder to between 85% and 90% of the prescribed test pressure. Warning: Do not exceed 90% [49CFR 173.34(e)(4)(v)] of test pressure.
3. Hold the pressure and determine that the system is free of leaks.
4. Release the pressure to zero.
5. Zero the burette again if necessary.
6. Proceed to retest the cylinder at the required test pressure.
7. Repeat this procedure with each hot dip galvanized cylinder to be retested.
This test system check procedure is specifically authorized under the provisions of 49CFR 173.34(e)(4)(v) and CGA C-1, Methods for Hydrostatic Retesting, 1.4.
This procedure is necessary to obtain accurate test results. The provisions of the PST Warranty therefore require that the cylinders are prepared for test and the system check is performed in accordance with these procedures. If these procedures are not followed in retesting hot dip galvanized cylinders, the owner should be given prior notice by the retester that the warranty may be invalidated by the retest.
Related test bulletin: PST Bulletin D101, Retesting DOT-E9791 or TC-SU4349-241 Advanced Technology Cylinders. PST high-pressure (3,500 psi.) cylinders have special test requirements based on their design and the DOT/TC requirements. This bulletin provides the necessary information.
Following this procedure will assure an accurate retest for PST SCUBA cylinders. If you experience any difficulty in obtaining acceptable readings, please contact PST SCUBA customer service.
These bulletins are provided free to all retesters approved by the US DOT or Transport Canada.

[JS1scuba]

There is no issue if people doing hydro know what they are doing and follow the proper procedure. Ask first. See below.

PST Technical Bulletin D101 Retesting DOT-E9791 or TC-SU4349-241 Advanced Technology Cylinders Revised 3/20/2000
High pressure steel SCUBA cylinders manufactured by PST must be reinspected and retested at least every five years in accordance with the Code of federal Regulations Title 49 CFR 173.34 (US) or CSA B339 (Canada).
PST high pressure (3,500 psi.) cylinders must be retested in accordance with DOT-E9791 or TC-SU4349 and have special test requirements based on their design and the DOT/TC requirements. This bulletin provides the necessary information.
1. The retester must have a current copy either DOT-E9791 or TC-SU4349.
2. Use a test adapter that matches the MS 16142(SH) port in the cylinder. Hydrotest Products Part No. 100-58 with o-ring is a suitable adapter. Adapters designed for 4,500 psi. Fireman's cylinders may not seal properly and should not be used.
3. The test pressure is 5,250 psi. DOT requires a test pressure of 3/2 times service pressure for all newer designs.
4. The wall calculations of CGA-C6 are not applicable to these high-strength steel cylinders. For the purposes of inspection criteria, the minimum wall for a new cylinder is 0.179 inch, the estimated actual wall at time of manufacture is 0.195 inch and the minimum wall in service is 0.172 inch.
5. Almost all PST high pressure SCUBA cylinders are hot-dip galvanized for protection from corrosion. Specific procedures must be followed for cylinder preparation and retest checks to obtain accurate results in retesting hot-dip galvanized cylinders. These are described in PST Bulletin D100, Procedures for Hydrostatic Retesting for Hot Dip Galvanized Scuba Cylinders.
Following these procedures will assure an accurate retest for PST SCUBA cylinders. If you experience any difficulty in obtaining acceptable readings, please contact PST SCUBA customer service.
These bulletins are provided free to all retesters approved by the US DOT or Transport Canada.

PST Technical Bulletin D100 Procedures for Hydrostatic Retesting of Hot Dip Galvanized Scuba Cylinders Revised 3/20/2000
Steel SCUBA cylinders manufactured by PST must be reinspected and retested at least every five years in accordance with the Code of federal Regulations Title 49 CFR 173.34 (US) or CSA B339 (Canada).
This bulletin describes procedures that must be performed prior to retesting each cylinder. The cylinder must be prepared and test system checked in order to obtain accurate results in the hydrostatic expansion retest of galvanized steel cylinders. All PST AquaAire SCUBA cylinders and older PST SCUBA cylinders made starting in 1952 are protected from corrosion by a hot dip galvanized coating. This hot dip galvanized coating may affect the readings from the hydrostatic test, therefore failure to prepare the cylinder and perform the test system check in accordance with this procedure may result in rejection of perfectly acceptable cylinders.
Cylinder Preparation Procedure:
1. Remove the plastic boot.
2. Remove any crusty white corrosion deposits. Crusty deposits are most likely to form inside the removable plastic boot if the owner has not routinely rinsed saltwater residue from this area.
3. Do not use aggressive acidic or caustic metal cleaners on the galvanized surface. The mottled gray-white appearance of used galvanized cylinders is normal.
Test System Check Procedure:
1. Visually inspect the cylinder, fill it with water and place it in the water jacket, as is your normal practice for any cylinder.
2. Zero the burette or expansion measuring system and pressurize the cylinder to between 85% and 90% of the prescribed test pressure. Warning: Do not exceed 90% [49CFR 173.34(e)(4)(v)] of test pressure.
3. Hold the pressure and determine that the system is free of leaks.
4. Release the pressure to zero.
5. Zero the burette again if necessary.
6. Proceed to retest the cylinder at the required test pressure.
7. Repeat this procedure with each hot dip galvanized cylinder to be retested.
This test system check procedure is specifically authorized under the provisions of 49CFR 173.34(e)(4)(v) and CGA C-1, Methods for Hydrostatic Retesting, 1.4.
This procedure is necessary to obtain accurate test results. The provisions of the PST Warranty therefore require that the cylinders are prepared for test and the system check is performed in accordance with these procedures. If these procedures are not followed in retesting hot dip galvanized cylinders, the owner should be given prior notice by the retester that the warranty may be invalidated by the retest.
Related test bulletin: PST Bulletin D101, Retesting DOT-E9791 or TC-SU4349-241 Advanced Technology Cylinders. PST high-pressure (3,500 psi.) cylinders have special test requirements based on their design and the DOT/TC requirements. This bulletin provides the necessary information.
Following this procedure will assure an accurate retest for PST SCUBA cylinders. If you experience any difficulty in obtaining acceptable readings, please contact PST SCUBA customer service.
These bulletins are provided free to all retesters approved by the US DOT or Transport Canada.

This is a standard procedure for hydro testing. What PST is asking is that the technician perform a "system leak test" for each cylinder. This essentially does a pre-stetch on the cylinder but because it does not go above 90% of test pressure the cylinder can't be failed if it does not come back to it's original shape. It can then be tested to full test pressure and in some cases the cylinder may come back.

Hydro test facilities calibrate their test equipment multiple times in a day with a specific calibration cylinder. It's important that the area where testing is being done maintains consistent temperature. If the temp changes during the day, a recalibration is usually done.

Cheers
JDS

<i own a hydro test facility - i dont personally test - we have technicians for it>