hydrotest VS pneumatic test

[Ahmedfromkuwait]

why hydrotest @ 1.3 X design pressure and pneumatic test @ 1.1 X design pressure.

[arcpro]

This is because of the difference in stored energy.
Pneumatic test has much more of stored energy due to air medium as compared to the test conducted with water.
Code limits pneumatic testing to 1.1 times design pressure as it would be sufficient to check the mechanical integrity of the system.

[mechcolor]

I agree with arcpro.
It must be having some safety reasons behind it due to stored energy.

[Ahmedfromkuwait]

The test pressure is dependent on design pressure. I dont think any relation with stored energy . Stored energy is calculated by P X V which will be depedent pressure & volume.

[ashfaqanwer]

Yes Ahmed, you are right. The test pressure depends upon design pressure but the reason of restricting the pneumatic test pressure to 1.1 times design would be having the only reason of stored energy. Code guys must have retained this factor to the minimum; otherwise I do not think there might be any other reason for that.
Code recommends pneumatic testing in lieu of hydrostatic testing when conducting hydro is not practical but at a reduced pressure as the failure would cause huge losses as compared to the failure during hydrostatic testing. Pneumatic testing is much much dangerous and extreme safety precautions be taken during the test.
Additionally, another reason of reduced factor of 1.1 would be the sensitivity of pneumatic test which is higher than that of hydrostatic test.

[SOHAIL CHAUDHRY]

Continuing previous discussion, i want to ask the feasibility of Hydro or Pneumatic test ? I mean where hydro/pneumatic tests are conducted (is there any service restriction) & pls provide me procedure of hyrdo test (methods of getting tank/vessel pressurized).

[ashfaqanwer]

Dear Sohail,
As per ASME B31.3 for process piping and ASME Sec. VIII for pressure vessels, hydrostatic test is recommended for the integrity check but there are few instances where conducting hydrostatic test is not a feasible option and is to be replaced with pneumatic test. Below are the few situations:
1. For cryogenic services, moisture is not desirable - complete drying not possible, freeze susceptibility
2. Piping or pressure vessel involving internal lining, refractory
3. Water level with acceptable chloride levels not available
4. Water cannot be readily dried and testing water cannot be tolerated
5. Environmental concerns - supply & disposal of water

[SOHAIL CHAUDHRY]

Thanx Ashfaq bhai for prompt responce ... but my one part of question is left that whether whether vessel in pressurized by high pressure pump or after filling with water we can get that pressurized by air compressor & one more important term is used that is air binding ? Pls explain

[ashfaqanwer]

I could not get your point properly. But will try to answer. Vessel can be pressurized by any high pressure pump suitable enough to build the required test pressure. Air binding inside the vessel shall be avoided while pressurizing. Vents must be sufficiently provided to serve the purpose.
You may clarify what exactly you want to know about so that I may better understand your point.

[SOHAIL CHAUDHRY]

Thanks Ashfaq bhai, i got what i wanted to have n sorry for late reply as i was on project site.