A challenge: leak detection on long-distance pipelines
The locating of leaks on long-distance pipelines is one of the major challenges for service providers and measuring instruments. With the “Ortomat MTC” correlating datalogger and the Hydroport system from the vonRoll hydro company some astounding results can be achieved. In contrast to local networks, there are usually only a few access points to the pipeline, meaning that measurement sections can extend over extremely long distances. In the circumstances, leak noises are not picked up or, because of the insufficient radio range of the correlators, cannot be measured. A role is also played by the different operating states of the pipelines – from standstill to high volume flowrates, occasionally also with widely fluctuating pressure ratios.
Transfer structures with interference noise from pumps or pressure reducers represent further challenges. Additionally, smaller losses of water are usually not recorded at all by the water meters as these fall below the measurement range of the metering devices.
Correlation with noises
The “Ortomat MTC” correlating dataloggers offer several advantages which make leak detection on such pipelines easier – and, in fact, possible in some cases where it was previously not possible at all. Correlation is done with noises which are recorded at night. This means that ambient noises from traffic and similar are minimised. A direct line of sight, as needed by normal correlators between the two transmitters, is not necessary thanks to the automatic synchronisation of the datalogger. This means that the dataloggers can also be used independently of each other and so bridge long distances.
The following data are recorded by the noise loggers:
– lowest noise level at night
– noise level every 30 min
– nightly noise recording at 2 am to listen and correlate
The first step is to evaluate the noise. Are there any particularly loud sections in the pipeline? However, especially with long measurement distances, often over 1,000 m, the noise level is only one indicator of a leak. In this case, correlation of the noise recorded at night is particularly helpful. Under good conditions (ambient noises, pressure in the pipeline) the correlation makes some astonishing measurement results possible with pipeline lengths of up to 2,000 m. On the basis of the measurement results, a rapid pinpoint location of the leaks can then be carried out on the spot, for example using ground microphones.
Example: The Oberfranken water supply company (FWO) in Kronach
There was a known leak on a DN 500 (ductile cast iron) transport pipeline with a small volume of water escaping to the surface. The measurement points were located 924 m and 1,066 m from the leak. Measurement conditions were good: the pipeline is in a rural, field area and the pressure was approx. 6 to 7 bars. Once the measurement section had been installed and set up in the Hydroport, good measurement results were able to be achieved even by the 2nd day. In the end it turned out that the leak was just 2 m away from the correlation result; with a measurement distance of almost 2,000 m, a creditable result! For the human ear, however, there was no perceptible leakage noise at either of the measurement points, even with a listening device. After excavating it was found that a collar with screwed socket joints had started to leak, probably because of subsidence. The water loss was around 2 to 5 m³/h.
Example: The Siegen-Wittgenstein water association (WVS)
A pilot project has been carried out by the Siegen-Wittgenstein water association in which numerous sections of pipeline were checked. But here again, good measurement results were able to be achieved. The first leak was measured on a section of pipeline which crosses a motorway and a very busy main road between two access points. Despite two changes of material (AZ-GGG-AZ) and radio connection being made impossible by buildings and noise protection barriers, a leak was successfully able to be detected. The “Ortomat MTC” was set up in the existing manholes by the motorway and in the main road; the pipe cover depth was approx. 6 m. Meanwhile the WVS has repaired the leak. The point along the trench determined by leak detection lay precisely above the damage location.
A second leak was able to be detected with pinpoint precision alongside a railway line; the distance between the measurement points here was 467 m. This was a pipeline of DN 200 ductile iron pipes of the first generation with inadequate corrosion protection. The repair, which was initiated immediately, was successfully achieved.
Correlating noise loggers make effective monitoring of drinking water transport pipelines possible. This means that, in the context of noise transmission, amazingly long measurement distances are investigated, which would have been unthinkable with previous methods.
The measurement results are continuously documented in the Hydroport. If it should actually come to cases of major damage, the constant monitoring of the pipeline can be documented for insurance purposes.
Manuel Görzel, vonRoll hydro (service) gmbh