How does HydroTesting unit work? I searched online alot but just found vendors who are selling it 2

[masieh2004]

Hello Guys:

I am curious to know how hydro testing units work. From the websites of the vendors, I found that it has compressor, pumps, valves, regulators, guages. I actually want to know whats happening inside of it. If you can provide me a link that has the working principle of hydro tester, I will really appreciate it.

Thanks
Mas

 

[racookpe1978]

What do you know about plant testing, and when did you learn it?

What is your foundation and experience?

 

[masieh2004]

I have almost no experience just have BSME.

 

[moltenmetal]

OK, this sounds like a very fundamental question. So I'll answer it the way you've asked it:

A hydrotesting device applies liquid pressure to the internal or external of device under test, to expose gross flaws in manufacturing or materials which may lead to leakage or premature failure.

It consists of a source of liquid pressure (generally a small tank and a pump), a means to regulate the output of the pressure source, a tight shutoff valve, a means to remove or vent the air that the thing under test used to contain, and a device to measure pressure.

 

[masieh2004]

MoltenMetal:
Thanks for your response. Your last paragraph helped me a lot actually. Do we really need air in this whole process? whats its role?
Does the liquid move inside the cylinder during the hydro test? Do we need a compressor too??
I know I am asking a lot that's why I asked for a link to source where I can simply read about this whole process.

 

[chicopee]

You do not want air in the liquid which would normally be water.

 

[Gilmiril]

During hydrostatic testing (aka shell testing), you want to fill the item being tested (e.g. a valve) with the test fluid (we use a water/glycol mixture) and evacuate all air from inside it. You then apply the test pressure, which is usually 1.5x the rated working pressure at room temperature, and hold it for a specified time (note: for API-6A 2000 and 3000 psi rated equipment, the test pressure is 2x the rwp). There's will only be liquid movement during the fill step and later while emptying the device after the test is complete. The intent of this test is to confirm the integrity of the pressure boundary.

You shouldn't need a 'compressor' unless you're doing a hydrostatic test using a gas as the test medium. I suppose there may be cases where that's required, but in the petroleum industry, that's not normal...at least not for a shell test.

 

[masieh2004]

Gilminil:

Thanks a lot. What about piston accumulator? Do we need that during this test? How will a piston accumulator help during this whole process?

 

[moltenmetal]

A poor, but sometimes inevitable, way to do a hydrotest, is the so-called "air over water" method. You fill the vessel with water, then introduce compressed air at a high point from a cylinder. Cheaper than a pump if you don't already have a pump capable of the pressure you need, but the resulting test is much less sensitive and can be more dangerous. While the water reduces the volume of compressed gas to a negligible amount IF you design the test properly, in any hydrotest the goal should be to have ZERO air in the vessel under test itself- limiting the stored air and hence the source of dangerous quick-release stored energy to the tubing or hose supplying the compressed air from the cylinder.

In a test entirely water-filled and without air, the test becomes truly sensitive: even a tiny amount of leakage will result in a large drop in pressure of the (nearly) Incompressible water and (somewhat) inelastic vessel.

It is better to think of both the water and the vessel as springs with really high spring rates, such that very small changes in distance (volume change resulting from compressing the water or elastic stretching of the vessel) result in huge reaction forces (pressure)- or vice versa. In practice the energy stored in those springs is quite small in a water-filled system, and is rapidly released by even small changes in dimension of the vessel under test, and hence that energy is not of much risk of danger upon failure- until the vessel under test becomes very large indeed. That is NOT true of a vessel tested pneumatically, which is why pneumatic tests must be done so much more carefully and to a smaller fraction of the design pressure.

An accumulator with diaphragm or piston can be used to allow you to apply air pressure to the water without having the air in direct contact with the water. This is important because air dissolves in water, which can tend to make pressure bleed away without the need for a leak, making the test look like a failure when there aren't any leaks or flaws in the vessel. But in this case, the diaphragm or piston system need to be capable of safely withstanding the results of a vessel total failure, where the air pressure on one side of the diaphragm/piston is the full pressure required in the test but the water side drops suddenly to near zero. It's not really all that practical unless the test pressure and/or volume are quite small. A pump is safer, and if you do a good job of removing air (sometimes that may require a vacuum pump) prior to the test, even a tiny high pressure pump will easily provide enough water to accomplish the test.

 

[1gibson]

Gilmiril, what kind of pump do you use to pressure up? I typically see air operated diaphragm pumps, which are driven by compressed air, meaning you need an air compressor if it is a self contained unit.

A link to whatever the OP was looking at, might help focus the discussion.

 

[moltenmetal]

The pumps we use are MaxP or Haskell air-operated piston pumps. They "multiply" pressure by having a large piston or diaphragm on the air side coupled to a very small piston on the water side, and can develop pressures up to 10-15,000 psig.

 

[zeusfaber]

There are two other methods - both quite similar and both commonly used for testing smaller vessels.

In one, the vessel under test is filled with liquid and then immersed in a liquid-filled container that is sealed except for a burette to measure the expansion of everything inside it.

Pressure (1.5 WP is still favourite) is applied to the inside of the vessel and the rise of liquid in the burette is used to determine how much the pressure has made the vessel expand. The pressure is then removed and the burette is read again to check that the vessel has recovered to its original volume. Anything more than (typically) 2% of permanent set is treated as a test failure (as is a burst or a leak).

The other variant seeks to measure directly how much liquid flows into the vessel when you pressurise it and compares this with the amount that comes back out afterwards.

A.

 

[bellowsmfg]

I highly recommend contacting the Compressed Gas Association (CGA) and obtaining their directives regarding Hydrostatic Testing.
They provide very detailed written and schematic information that will give you the guidance you need.

Bellows Manufacturing and Research, Inc.

https://bellowsmfg.com

 

[racookpe1978]

I will return to my first question, and your answer to that question.

Because you have no experience with the very dangerous, very complex minor issues and problems associated with deliberately filling and then OVERPRESSUIZING your plant system with water, gasses, and non-vented residues during complex procedures irregularly performed, but performed at the end of long outages on new piping and new systems while udner extreme time and budget pressures ...... You are asking for trouble and probable plant loss if you do the testing wrong.

the REASON many companies on-line are "selling" their services and their expertise is because they have knowledge and experience that you (your company!) does NOT HAVE. Yes, their services are expensive. These companies frankly do not want to give you their knowledge for free. Our experts here have attempted to help - but your experience level is not sufficient to let me believe you (your operators) know enough to do the job safely and to the proper pressure WITHOUT EXCEEDING the correct test pressure.

Yes - If you go too far, you will damage your plant. If you do not go to a high enough pressure far enough through the system for a long enough periof of time, you have not certified your plant.

These companies are expensive.

But many million dollars less than destroying your plant doing the hydrotest lineup, filling, venting, pressurizing, testing, certification, venting, draining, and restoration of normal startup valve and pump and vent lineup properly.