Hydro Test

Oh Yes, besides the welded joints there are flanges and couplings.

In one practical instant pipes buried 5 feet below ground qualified welding tests, however the pipe lengths were resting on sand bags in order to provide room for rust protective coatings which was done but somehow the areas in contact with sand bags were left uncoated and could not be detected in spot tests. There had been a delay of few months in commissioning, by that time the unprotected spots were sufficiently corroded, and when the pumps started, water shot up even from under a cover of soil.

Absolutely yes

In all codes and standards, the radiography can't be substituted or in lieu of hydrostatic test pressure, but in certain cases, the pneumatic test can be carried out in lieu of hydrostatic test.

I'm guessing...Pneumatic test is mostly done in the case of low MAWP.

Where can I find a basic procedure of the Radiography test..?

"Pneumatic" testing should NEVER be used- a system failure could be catastrophic with the compressed air in a dramatic rupture. Additionally, any "leak" would not necessarily be found because the pressure loss of significant compressed air will not often be high enough tp be observed.

HYDROSTATIC testing involves filling the pipes / tanks, etc to be tested with water and then applying a small amount of compressed air pressurization of the flooded system. System failure will be easy to find because the pressure will fall quickly and the leaks will be small drops of water- easy to spot. Also- catastrophic failure will only dump a bunch of water somewhere, because the pressure will be released almost immediately.

Hi..

Theoretically we can do either hydro or pneumatic tests. However high pressure pneumatic tests are best avoided for safety reasons unless it is mandatory to use air as the testing media in any special application.

In large diameter low pressure overhead lines we resort with air leakage tests wherein the leakage is checked over a 2hour or 4hour period e.g. the overhead Blast Furnace & Coke Oven Gas lines in Indian steel Plants are of 2 meter or more in diameter and subject to air leakage tests only.

I am sure that the reason for pneumatic-only testing only is that the piping supports were not designed for the extra weight of a flooded pipe.

I once witnessed a pressure test of an approx. 50CM piping system that was SUPPOSED to have been hydro but the mechanic didn't want to deal with the water draining. Aside from a longer time to DO the test- compressed air, then several cylinders of nitrogen- near the end of the test set-up, one of the pipe joints failed. It was at the base of a 12 meter riser. That 12-meter riser was launched like a toy rocket and went over 75 meters up before crashing back to the ground. Fortunately, no one was injured but the launch caused over $US 10,000 damage to the superstructure holding the pipe.

A hydro failure would have just been a bunch of water at the base of the riser.

Line sizes of up to 3 and 4 meters?

When you are talking industrial grade many things change. The systems are designed knowing how they will be tested.

Not sure where lines 3 or 4 meters came from. Post 8 spoke of lines 2 meters and over, and my comment was regarding a line 20-inches (~50 CM) in diameter.

In response to your statement that hydro tests HAVE to be used otherwise things will blow up.

Hydro tests should be used where they are practical and possible.

Hi..yes, the pipe supports are not designed to carry the weight of water. An old style 3500 cubic meter capacity Blast Furnace is able to supply lots of waste gas rich in carbon monoxide. The low pressure gas is extensively used in reheating furnaces. At Bhilai there are several kilometers of 2.2 meter dia BF gas & Coke Oven gas lines: operating pressure = 800mm of water column. These lines are pneumatically tested at test pressure=2000mm of water column for leakage over a 2hour period for out door lines. Max allowable leakage was 2% in 2hours. The test formula was the same old Boyle's Law P1/T1=P2/T2 wherein P & T were absolute pressure & temperature. Extra test precaution is necessary because the gases are toxic.

Further more in such large diameter lines finding enough water to fill-up is a problem especially in arid zones and where the sea is far away. Although in an atomic power station we had to hydro test large dia underground cooling water lines as these were operating under pressure.

Thanks for the qualifier.

A test at 250% of likely operating pressure will definitely show any risk of leakage.

Never heard of 250% - 1.5 * design pressure is the norm and perfectly adequate.

The testing norms in this case were acc to GOST - Russian Standards of the former Soviet Union !

Your question "where can you find a basic procedure of the Radiographic Testing. There is no standard format available in any Code. You would have to develop yourself. Same like WELDING PROCEDURE QUALIFICATION. In Radiographic Testing Procedure you prepare a sample Radio graph on the pipe weld, the radiography is going to be applied with the radioactive source that you plan to use. In Radiographic Testing Procedure you make a record of the following information and shoot a weld joints or castings, with type of film you are going to use. Since sensitivity of the Radio graph is very important to evaluate a defect present in the weld or casting, Radiographic Testing Procedure is required to give assurance to the Client that similar radio graph would be prepare on your project. Prepare a demography with following information. 1) Radiographic Contractor name, Radiographer name and Level according to ASNTC 2) Buyer/purchaser/client name 3) Project name 4) Date on which procedure established 5) Type of source X-Ray or Gamma Rays 6) Source strength (Curies or Watts in case of X-Ray) 7) Type of Film, film size and number of film on each joint used. 8) Type of film cassettes, thickness of front and back lead screen 9) Type of penetrameters, number - source side penetrameters and film side penetrameters. Penetrameters should be of same metal as of object being radio graphed. 10 Source film distance 11) Type of Image (DWSI or DWDI - Double wall single image or Double wall double image or Panoramic shot. 12) Detail of object being radio graphed - welds joint, thickness pipe wall, forged item etc. 13) Exposure time 14) Processing chemical temperature 15) Processing time, immersing time in developer, fixer and wash. 16) and then the last is readable sensitivity of the radio graph in H & D unit (Hurter and Draffield) I am sorry if I have spell name of two scientist wrong. You make a record of the above information and this is your Radiographic Testing Procedure.

Radiography test is conducted for the purpose of detecting any possible opening/unsealed joints while hydrotest is used not only to detect possible leaks from the pipe but also to check if it can withstand the pressure in the pipe.

RT is just done on welding joint, but if the defect is on the base metal??! ihad experienced this situation before.

Oh yes yes. The hydro test is done to determine the integrity of all the components in the system. If the materials do not have sufficient strength they will not be able to hold the applied pressure hence failure. Remember your material certificates represent the samples taken. Anything can happen during manufacturing and the product might not be as strong as the samples.

As someone pointed out - large diameter process gas lines (inside the plant battery limits) and large process equipment, even if it could be considered a pressure vessel, are subjected to an air pressure test.

Case in point being an iron ore direct reduction furnace of up to 7.5 meters diameter with connecting ducts of 2.5 to 3 meters diameter.

If practical a pressure test using water is always the preferred method.

Pressure Vessel is designed to ASME Sec VIII Div 1 or 2 which ever, similar to BS and EN or JIS standards the Hydrotest is mandatory. RT is limited to the weldment not the overal integrity of the vessel to which it is designed. Certain cases Pneumatic test is adopted in lieu to hydrotesting. Futhermore would like to advise you that is you are dealing with big vessels, the foundation settlement is also an issue for which on-site hydrotest becomes the only method to ensure that the vessel satisfies the design and purpose.

Regardless the applicable Code, there is a main difference that will make you understand why these two are different and therefore one of them doesn't substitute the other:

Hydrostatic test is a "strength" test, in which you put a Code required pressure, usually expressed as "1.x" times the design pressure, to check the strength of the vessel is enough to be accepted under that Code.

Radiographic NDE of weld just give you information on the absence of heterogeneities inside the weld seams, but nothing about their strength.

Kind regards

Yes, one is a non-destructive test the other is a destructive test in ways ie.. a failure while performing the hydro. Its not like api 1104 pipelines where radiography @ times can be used instead of bend test.

Defining hydrostatic test as destructive testing is not correct. You may call it as strength test. Destructive testing is the one when applied, the material under test is either disintegrated, broken, change original shape or lost. This is well witnessed when you cut coupons from a 'test-weld' and subjected to tensile, root bend, face bend, side bend and V notch etc where as radiographic testing is nondestructive testing.

RT is only for weld seam. Base material also should be tested by hydro test.

I think itis necessary