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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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, ~

q>~

Q-

,

.. I J:J ~ ~

::>

... ..i' "

)

VACUUM METHOD

... 1 ~ e

", l

~ 'f- r- ....

,

II

r-:--

r-I-<

VI c 0

:.:: .... .. '" ... ...

§

,

t--

-.....

WORKSHOP SITUATION.

I

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FIG 2

.. '" -,. :.

II'

Q,

E

l)~ '- ~ 7 >

,

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leaking liner section

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V ACUUM METHOD

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PLANT SITUATION

U tube .--

v~cuum

pump

__ 6 -t.., ,_, . , :,~ . . ,_,_,.;:OJ ,'=, .• '_

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FIG 1

'-­

ammonia

. - ....ater

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FIG 3

PRESSURE METHOD

'v.-c: - It ,[::

~./ J ~ ~V~V ' ~~M

CE '- ... , ~ , , ,

AI "c , , , -a... , '" )I

g ( ,-) '§

, , '" , , .... , ,

I V I-~ , 1

I

~ , . , . , .

7

" '" ~./ I '~ "" e '" •

, , . , , ,

I • • .

a... / ,

, , , , ,

I

t:( V V ~ V V V v/

~ l/ ~

-

WORKSHOP SITUATION

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PRESSURE METHOD

'-17~-

-~~ - V PI ,

?-~ 1/ V V / VJ"V , , ' ,

, T , , ' ,

I

I I ,..., .... , I

I . , ,

I L--

I ammonia

, ' , , I

I , . , , . , I

• A .. V '/ r/ V V V V '/

~ ~ r/

. .,ELANT SITUATION

..,.".-

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FIG 4

~ ,...,...,

l.-

nitrogen

runninq ',later

f