4 replies to this topic

[deltaChe]

Dear Sir/Madam :


I have difficult in understanding test pressure in tightness test. Tightness test is applied to the piping system whichhandling harzdous, chemical, and hydrocarbon process fluid. (Note. vent, drain or piping open to atm, pressurevessel,heat exchanger, pump, turbines, compressor, blower is not included)In my case, air test pressure is used 5kg/cm2g when the normal operating pressure is 5 kg/cm2g or more. First,connecting air supply to point, and pressurizing the system up to 5 kg/cm2g, then disconnectting the air hose, then checking all joints (such as threaded, socked-welded, butt-welded and flanged) for any leaks by spraying soap suds.But, it confuse me that the difination of test pressure written in ITB pneumatic test.

1. Preliminary air test not more than "1.7 barg" may be made to locate marjor leak befroe a hydrostatic test.

2. Pressure to "0.5 barg" and hold for a sufficient length of time to allow piping to equalise strains.

3. pressurise gradually in 10% steps to 60% of the specified test pressure and holdfor a sufficient lenghth of time to allow piping to equalise strain.

4. Reduce pressure to 50% of the specified test pressure and visuall inspect all joint leaks.

5. The test pressure shall be helld for 2 hours and then reduced to design pressure after wich all joints shall be inspected for leak with soap sud.

6. The pneumatic "test pressure" sahll not exceed "110% of design pressure".

As the operating pressure in pipe is greater than 5 kg/cm2g, I am not quite sure 5 kg/cm2g as test pressure is right or not.
If there is a pipe whtich operating pressure is 10 kg/cm2g, which is correct test pressure to be used for air tightness test?

Should I used 5kg/cm2g or 110% of 10kg/cm2g as air test pressure or hydraulic tightness test instead of air tightness test in this case? And, why is that the liquid testing medium always be instroduced at the system low point? How can this to avoid air pocket formation ?

Your generous help is always appreciated.

Edited by deltaChe, 24 December 2011 - 04:50 AM.

[ankur2061]

deltaChe,

Pneumatic test should be conducted at low pressures and not at high pressures. Refer the links below for some explanation on pneumatic testing:

http://www.cheresour...__fromsearch__1

http://www.cheresour...1579#entry41579

Hope this helps.

Regards,
Ankur.

[kkala]

http://www.cheresour...rleaktest.shtml gives also guidelines for leak test.
-Final test pressure should not be lower than 1.1xdesign pressure (1st link of previous post).
-Air pressure is gradually increased to final test pressure, intermediate results are assessed (my info).
-I understand use of liquid does not concern a pneumatic test and (when needed) it has to be introduced at the lowest point, with a vent open at the highest point of piping. Just to have all pipe full of liquid, avoiding air trapped in the pipe.

[deltaChe]

Dear Sir/Madam

There is a air tightness test pressure rule setting by the senior engineer (in the following),

1. If the normal operating pressure <5barg, the test pressure should be used design pressure or

safety valve set pressure - 1.5barg (depend on the design pressure or PSV set pressure which one is

lower)

2. If the normal operating pressure > 5barg, the test pressure shoud be used 5barg. But, this rule

seems contridict the description in ASME B31.3. The following description is extracted from ASME

B31.3

1.The pneumatic test pressure shall not exceed 110% of the design pressure.

2.The preliminary air test to not more than 17barg may be made to located major leak before a

hydrostaic test.

For example, the design pressure is 2barg, and operating pressure is 1barg. So, is that mean

that the test pressure for air tightness test is 2-1.5 = 0.5 barg ?

I am not sure that the test pressure (0.5 barg) will be too small for air tighntess test or not.

Your help is much appreciate. Please help me to correct my understanding if I have any wrong.

Thank you very for your time

[kkala]

Having no practical experience (only limited office info), I can only tell opinion / comments, for want of more precise information from somebody having the knowledge. Direct communication with the senior engineer could clarify points.

There is a air tightness test pressure rule setting by the senior engineer (in the following),
1. If the normal operating pressure <5barg, the test pressure should use design pressure or safety valve set pressure - 1.5barg (depend on the design pressure or PSV set pressure which one is lower)
2. If the normal operating pressure > 5barg, the test pressure should use 5 barg.
Are above "rules" written? Do they aim at a rough preliminary leak test (not the final)? They may not be clearly expressed, ask for aritmetic examples. Applicable code can also play a role (ASME B31.3 or other?).
But, this rule seems to contridict the description in ASME B31.3. The following description is extracted from ASME B31.3
1.The pneumatic test pressure shall not exceed 110% of the design pressure.
http://www.cheresour...-test-pressure/ - post No 10 specifies pneumatic test pressure between 1.1*design pressure and "1.3*design pressure, or pressure causing 90% of yield stress, whichever is lower" per ASME B31.3 (2010). Clarification from "experts" is welcomed.
2.The preliminary air test to not more than 17barg may be made to locate major leak before a hydrostatic test.
OK, this is preliminary test, it seems you can chose a pressure up to 17 barg (even 5 barg), taking design pressure into account. Final leaking test will be contacted at the proper pressure.
For example, the design pressure is 2barg, and operating pressure is 1barg. So, is that mean that the test pressure for air tightness test is 2-1.5 = 0.5 barg ?
I am not sure that the test pressure (0.5 barg) will be too small for air tighntess test
If normal operating pressure is 2 barg (para 1 speaks of operating, not design pressure), design pressure can be 2+2=4 barg and test pressure 4-1.5=2.5 barg. Test pressure would be same considering design pressure, or PSV set pressure (being the design pressure in all but exceptional cases).

Edited by kkala, 01 January 2012 - 08:20 AM.