Compressors and Pressure Build-Up Capacity

Firstly, has the line been tested hydraulically to a point above this pressure?

If so, to what pressure?

If not, then why not?

Thank you for your prompt respose.

As per the specification test plan, the compressed air line shall be tested minimum 1035 KPa or 345 KPa above the working pressure by compressed air. the working pressure is 8 bars

Please see the following spec clause

"3.9 FIELD QUALITY CONTROL

2. Piping Leak Tests: Test new and modified parts of existing piping. Cap and fill

general-service compressed-air piping with oil-free dry air or gaseous nitrogen to

pressure of 345kPa above system operating pressure, but not less than 1035kPa.

Isolate test source and let stand for four hours to equalize temperature. Refill

system, if required, to test pressure; hold for two hours with no drop in pressure.

a. Repair leaks and retest until no leaks exist."

Never mind that. Has the line been tested hydraulically to a point above this pressure? If not, then why not?

Hi PWskack,

Leave the testing part. specs calls for only air or nitrogen.

My question was about air compressor. For instance ,If I buy a 2 HP or 3 HP compressor with certain CFM discharge at say 100 PSI, how can I make sure that I can build up a pressure of 12 bar from this compressor to my installed piping?

Ascertain first that the line will withstand 12 bar safely without spontaneous, explosive, and spectacular self disassembly that could injure, maim or kill, by carrying out a hydraulic test to a higher pressure!

_{Is there no sense in this world?}

<unsubscribes from topic>

PWS is right and you must take what he said seriously.

When you want to test the pipeline with compressed air or any other gas, it must be checked with liquid first.

In case of failure and leakege, the expansion of the comrpressed volume is not only potentially but extremely hazardous. It will explode like a bomb.

Hence plese ensure the hydraulic testing of the line at the required over pressure and proceed only after ensuring.

As far as the second part is there, the compressores are rated for what pressure? If these are for 10bar, it must easily be able to pick up the extra 2 bars provided you check the over pressure settings (at least our shop floor compressors have the relays as well as the reliefs) and reduce the flow.

If it is a lower rating one say 6 bar then whether it can or not depends on type of compressor and also the motor rating. If it is any positive displacement (screw compressors or any of various other rotary compressors) it must not be a problem.

Else the other choice will be putting an inline booster compressor.

But first follow PWS.

12 bar is 175 PSI. Thats standard issue commercial compressor pressures. Typically they are two stage units though. The small portable cheapo single stage ones are likely what your finding that have a 100 - 130 PSI top end limit.

There are countless small two stage units on the market. Check with your local site workers and find someone who has a truck mounted engine driven commercial unit. they typicaly run with 175 PSI or slightly higher top end pressures.

Another option is to get a tank of nitrogen from a welding supply center and rent the correct regulator that goes with it. Typical nitrogen tanks are around 2200 - 3500 PSI.

However seriously look at doing the hydro testing first! And if its not legally required at least get every body out of the building during the testing! Odds are you will be fine but sometimes stuff happens!

You can try to increase the pressure with adding an preesure booster temperarily.

PWS and SB,

Agreed doing hydro prior to pneumatic is a good engineering practice, but it is not mandatory. In many plants sometimes we only do pneumatic, typically for gas fuel and comp air lines. It is also allowed by code under special circumstances and client requirement is one of them. The major concern is the corossion caused by tell tale water left after hydro on lines which normally handle gases.

Reg getting 12 bar, it is not a problem for most of the compressor packages, particular screw or recip. The key is how would you isolate the air receiver which normally has a PSV set at 10 barg. Have you got a bypass around it?

The PRVs can be reset to 12 bar, unless it is a Safety valve.

The PSVs normally are also spring loaded and can be reset and then checkd for setting.

At least most of the ones that we have in our lines have that feature (our standby compressors- usually used for testing when common line pressure 5bar do not suffice- are normally at 6bar but some times we do go up to 8-10 bar and reset the PSV on those occasions and remember to reset back once it is over. We use pressure gauges for this purpose, a couple of them (in addition to the header gauge).

The PSV set pressure can be varied within a range. But each time it is reset you got to retest in the shop and re-certify it, which is a pain. What is the practice there?

Just a bit easy for us, since we have our own calibration labs. (This setting for the air line portion is only a bit less than a fraction, those guys have to do all the things around with the PRVs etc used for the actual product).

In fact we have earlier thought about having a couple of these with different set values, but the requirement of the resetting is not very often.

Now what we do is to have an adjustable pressure controller which trips the compressor when the pressure reaches 6 bar (or 10 bar) as the case may be. All the lines are any way sufficiently over-rated so no safety hazard (in fact these are all Seamless SS tubing with swagelok fittings and will take hydraulic pressures several times higher), and since it is only equipment testing (operation on set pressure) a bit plus/minus are acceptable.

But then if it is pressure testing then it is another matter.

I guess if the need arises then we will go for sets of Safety valves set at different pressures.