ammonia leak test

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1. Introduction.

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Leaks can be traced by using ammonia as a tracer and allowing it to react ~.th a developer. A leak will show up by change of colour of the ~Suitable developers are ammonia sensitive paper, paint or spray.

developer.

The helium test is more sensitive than the ammonia test, but the ammonia test is preferred for its performance in moist spaces, where the helium test just does not work. The helium test shall be done before the pressure test. the ammonia test shall be done preferable after the pressure test.

The sensitivity of the ammonia test is greater than that achieved in a freon test; also the presence of freon at higher temperatures (e.g. in case of welding) forms chlorides which might lead to stress-corrosion cracking of stainless steel.

No te: bar is understood to mean the absolute pressure.

2.Teat methods. The ammonia test can be applied in two different ways,depending on the particular circumstances:

2.1 Vacuum method 2.2 Pressure method

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2.1 Vacuum method

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This method is based on the use of pure amoonia and may be applied to spaces that a re not too large, the air within which can be evacuated down to app r oximately 70 millibar. The method is particulary suitable for loose liner vessels, where the test pressure must be not too high in order t o avoid buckling of the liner.

2.2 Pressure method This method is based on the use of a mixture of nitrogen and about 15 % by volume of ammonia.It is applied when large spaces have to be filled, e.g. to check tube to tubesheet welds and a vacuum less than 70 millibar is not permitted.

In order to avoid explosion hazards, spaces must first be purged With nitrogen bef ore ammonia is admitted.(explosion limits of ammonia in air are 15 and 29 Yo by volume)

Do not use copper or copper alloys for parts coming in contact with ammonia.

3. Cleaning Before the ammonia t est is started, the surface on which the developer is to be applied must be carefully cleaned with a detergent or a solvent and dried. This is to remove oil, grease and alkaline substances (welding slag) to avoid misleading detection.

4.Safety For safety reasons this specification should be completed by the person and/or company performing the test and this should be done in accordance with local regulations and laws. The recommandations are therefore by no mean. complete and the relevant regulations should be studied.






S.Description of test procedures.

S.l.Vacuum method -Make connections in accordance with either figure 1 or 2.

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If there are more than two leakdetection holes per liner section, all other holes may be connected to the vacuuc pump. However, it is also possible to use only one hole and to plug the others.

-Evacuate the air between pressure shell and liner with the vacuum pump until a pressure of 70 millibar is reached.

-Supply gaseous ammonia until it emerge8 from the outlet of the vacuum pump.

-Stop the vacuum pump and continue to supply ammonia.

-Open the valve in the line to the U-tube as soon as the pressure becomes atmospheric.

-Now the ammonia pressure may be increased to 1.03 bar. Note: take care to ensure that no liquid ammonia enters the equipment. For this reason, the ammonia cylinder should be positioned vertically and ammonia should be admitted only gradually via a pressure reducing valve.

o.:.,~u Ll.~ LeoL Iv. "."0"".", L\,e .""I'VU"" dW"i..~ V H)' .. mall leaks wl1~ be rather long. about 10-12 hours. Therefore, :lpply the developer to the weld seams inside the equipment only during the last two hours of the test. Check for leaking ammonia during the response time. Note: before entering the vessel adequate safety precautions should be taken.

-Upon completion of the test remove the ammonia by means of the vacuum pump (U-tube valve to be closed), the outlet of. the pump running to a safe location or into a tray filled with water.

-Disconnect the 3t1l111onia' cylinder and admit air. When all ammonia is removed stop and disconnect the vacuum pump.





5. 2.'Pt:easure met;hod - Make connections in accordance with either figut:e 3 or 4.

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-Rais e the pressure around the tubes with nitrogen to 3 bar and depressurize . Repeat this procedure so as to be sure that the ammonia pe r centage is outside the explosion range.

-Raise t he pressure to 2 bat: by means of nitrogen.

-Supply ammonia until the pressure is 2.3 bar. Note: take care to ensure that no liquid ammonia enters the equipment. For this reaSon the ammonia cylinder should be positioned vertically and ammonia should be admitted only gradually via a pressure reducing valve .

-Given the low test pt:essure, the response time for very small leaks will be rather long, about 10-12 hours. Therefore apply the developer during the last two hours of the test. If ammonia sensitive copying paper is used and the tubesheet has protuding tube ends, it is not possible to localize leaks round the tubes; when an indication is found, the developer should be applied ca refully to the area in question to localize the leak more accurately. Check for leaking ammonia during the response time. Note: before entering the equipment adequate safety precautions should be taken.

-Upon completion of the test, the equipment should be depressurized by means of a tube dipped into a tray containing running water. Open the

-When the pres sut:e has reached a value of 1 bat:, removal of ammonia should be continued by purging with nitrogen so that the pressure is raised to 3 bar and deprssurize; repeat thiB to ensure that the ammonia concentration is out side the explosion range, follo~ed by purging ~ith air untill all the ammonia haB been removed









6.Developers The f ollowing developers have been succesfully in the past.

6 . 1.Ammoni3 sensitive copying paper.

6.2.Ammonia sensitive paint

Supplier Societe Sud Me.rine 41 Boulevard Gay Lussac 13309 Marseille, Cedex 3 Fr3nce tel. 989025 telex 41679

6.3.Ammonia detecting spray

Supplier American Gas and Chemical Inc. 5 Tenakill Park Cresskill New Jersey 0726 USA tel. (201 ) 569-52000

6.4.Ammonia sensi~ p~\ste

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the following recipe produces a makeshift substitute which may be used in the abs ence of the above mentioned products. 1 dm3 water 150 gram barium sulphate 50 em3 phenolpht3line (1.5 r. solution in spirit) 20 gram cellulose wall papering powder.

Colour change: white to purple.

The sensitivit y decreases after 2-3 hours, due to )ollli)

pasta drying out. p",~~ P' er r;me = 3-4- hl"

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ammonia leak test

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