Manual Aqua M300D
page 32
16.1.2.2 Pinpointing the Leak by Using a Ground Microphone
If you have managed to detect a defective pipe section using the stick
microphone, you can use the ground microphone to pinpoint the leak.
Always make sure that the distance between any two points that you
have selected for the ground microphone are not too far apart as
otherwise you might miss the leak. As a rule, the distance apart should
not be more than one metre.
16.2. Leak Detection with Trace Gas
16.2.1 Functional Principle
The optionally available H2 hydrogen hand sensor is excellently suited
for trace gas detection in combination with the Aqua M300. In such
cases, the pipe subjected to inspection is flooded with forming gas, type
95/5 (95 % nitrogen, 5 % hydrogen). Due to its specific structure,
hydrogen is able to penetrate almost all materials such as earth,
concrete, tiles, etc.. It can then be easily traced at the surface with the
Aqua M300 and the connected hydrogen sensor. Forming gas, type
95/5, is neither toxic nor inflammable. Therefore, it can be considered
harmless for leak detection operations and can even be used in fire-
protected industrial areas. However, please make sure that you follow
the rules and regulations that apply to such areas.
16.2.2 How to Carry Out Leak Detection with a forming Gas
After the pipe subjected to inspection has been emptied, the gas bottle
is connected and the pipe is then filled slowly from one end until the
hydrogen sensor at the other end of the pipe section or at a control point
along the pipe signals that gas concentrations have been detected.
Then the second end is sealed and the pressure is gradually increased
until the inspection pressure has been reached. It might then take
several minutes or even hours for the gas to reach the surface. This
depends on the leak and on the type of ground and surface. It takes
approximately 60 minutes for the gas to reach the surface when ground
in green areas, for example, is slightly moist and the pipes are about
1.5m under the ground. You have to follow the path of the pipe
repeatedly until the gas escapes through the surface. Then look for the
highest concentration within the area where the gas has escaped and
mark this point as the position of the leak.
16.2.3 Determining Correct Quantities Using Experience Gained in
the Field
Wif a pressure test with water has already been carried out on the pipe,
then the pressure at which water no longer escapes through the leak ca
be used to calculate the required quantity of gas — if not, the operating
pressure can be used.
On this basis and with the help of the volume table below, it is possible
to calculate the maximum amount of forming gas required to locate the
leak:
Formula: G = VL x L x D
with
G =
Amount of gas with regard to inspection pressure (L)
VL =
Volume in litres with regard to 1 metre of pipe length (L)
L =
Length of pipe (m)
D =
Inspection pressure (bar)
Example:
A DN 125 pipe is 300 metres long and is to be filled with a pressure of
approximately5 bar:
Volume per metre x length =
12.27 litres x 300 metre =
3,681 litres at a pressure of 1 bar.
At a pressure of 5 bar: 3,681 litres x 5 bar = 18,405
litres
As a standard 50l bottle contains 10,000 litres of gas at 200 bar,
approximately two such bottles of forming gas are required for the above
example.
You should also keep in mind when planning how much gas you will
need that in addition you will need a reserve for the gas that escapes at
the leak.
Volume table of various pipe diameters for calculating the gas amount
Pipe diameter
VL (volume in litres with regard to the
length of the pipe section in metres)
in mm
40
1.26
50
1.96
60
2.83
80
5.02
100
7.85
125
12.27
150
17.66
200
31.40
250
49.06
300
70.65