Burst location and leak detection in the supply network in Vienna, Lower Austria and Burgenland

Key facts at a glance

For water suppliers

The call usually comes the same day: the pressure in a part of town drops, a service connection reports discolouration, or the service reservoir no longer reaches its level. What you need is not a guess but a chalk cross on the asphalt: the damage is marked on the surface, and the trench can then be planned for that one point instead of opening the run along its length. How deep the main lies we do not state – that is in your asset records. CFT does not excavate and does not repair. We work in Vienna, Lower Austria and Burgenland with our own staff: a short journey and appointments at short notice.

For you as a business

On industrial sites, in fire main rings and on association mains, further constraints are added: machine noise that makes a low-noise time window necessary, arrangements with the works fire brigade, access rules and safety inductions. That is settled before the job, not at the gate. For framework agreements the service can be described by segments and days on site, separately from the water loss analysis that precedes it.

How the job runs

1. Narrow down. From consumption volumes, pressure traces and valve positions, the section carrying the loss is determined. If a leakage profile from a water loss analysis is available, the job starts there.

2. Settle the route. Where the main lies and what material it is made of is known to your water supply supervisor. This information comes from you and is the basis for everything that follows. If it is not known, or only imprecisely handed down, the location work takes longer – that is the most common reason for a job running beyond its frame. On request we record the route ourselves, with ground penetrating radar.

3. Prelocation under operating pressure. The segments are correlated, or we listen our way forward fitting by fitting – from surface box to surface box, with the Saalbach listening stick on the spindle. Where the noise level rises against the neighbouring points, the section is narrowed down. Where background noise is high, a low-noise time window is agreed.

4. Pinpointing. On the narrowed-down stretch the ground microphone follows on a close grid until the noise maximum is unambiguous. If no leak noise appears at all, it goes no closer – then the decision on tracer gas is due, and that one needs preparing.

5. Mark and hand over. The point is marked on the surface and recorded in the report. You get the documents before the trench is opened.

Equipment and methods

Correlation measurement under operating pressure

Two sensors are placed at accessible points on the same section, for example at gate valves or hydrants; from the difference in travel time of the leak noise, the position along the line is calculated, even where plastic damps the noise at the surface. What is needed is two points at which the sensors can be coupled, and reliable data on pipe length, material and diameter.

Preliminary listening at the fittings

Where no correlation is made, listening is done: from surface box to surface box, every fitting individually, with the Saalbach listening stick standing on the spindle and carrying the noise from the main upwards. The comparison is not against an absolute value but against the neighbouring points – a raised level says in which direction to carry on. This is the prelocation, not the point itself: it narrows down the section in which the ground microphone then works.

Pinpointing with the ground microphone

Escaping water produces a flow and friction noise at the damage that spreads through the pipe wall and the ground. The ground microphone is set down on a close grid over the route and searches for the maximum; that is where the mark is set. PVC and HDPE damp the sound strongly, low operating pressure makes the noise quieter, and machine noise masks it.

Leak location with tracer gas

Sometimes no leak noise appears at all: the loss is too small, or the main lies in a low point where the escaping water produces no usable sound. Then the way through is the gas. The section is charged with tracer gas; it rises through the ground and emerges – depending on how sealed the surface is – directly above the leak, where the detector shows it.

The section has to be taken out of service for this. That is not a side condition but the actual effort of the method: beforehand the section is shut off, all service connections are closed, and every adjoining property owner has to have been notified. Only then can the gas be introduced.

The notification is not our business. It lies with the municipality, the water supplier or the water supply supervisor – that is, with whoever knows the connections and their owners. Without this preparatory work no measurement is made; it therefore belongs in the scheduling and not on the day of measurement.

Route locating with ground penetrating radar, on request

As a rule the route and the material come from your asset records. If they are missing, we can search for the main ourselves: ground radar records layer boundaries and objects in the subsurface and so makes visible even runs that appear on no plan and take no signal. In cohesive or wet ground the penetration depth decreases, and the radar image is interpreted, not read off. This is a separate item and not part of the leak location.

Costs and effort

The effort depends on the network section, the pipe material, accessibility and on whether a prelocation is available; the cost range is agreed by telephone before the job. Buildings insurance does not usually apply here, because the damage is in the supply network.

Frequently asked questions

Contact and opening hours

CFT Group GmbH, +43 (0) 2252 53169, Monday to Thursday 8:00–16:30, Friday 8:00–12:00. Outside office hours in writing to office@cft.at; we will come back to you on the next working day.