Trace gas for pipe defect detection

Every defect in the pipeline, usually a water supply, will negatively affect the operation of the household or company. Whether it is an accident or a minor long-term leak, the requirement of the owners of the building is, of course, the quickest possible removal of the defect. First of all, however, it is necessary to find the place where it is located. And the method using a mixture of hydrogen and nitrogen seems to be the most accurate technology today to locate such defects.

Detail of a part of a PVC pipe, water supply to a foil pool, damaged by frost.

AKVAHELP METAL, with a 25-year tradition, designs, manufactures and installs stainless steel pools and pool technologies in both the private and public sectors. In their field, they increasingly encounter the need to locate problems related to water pipe leaks. Whether it is new buildings or older buildings of swimming pool operations, the owners find that the water leak usually occurs only when ten or more cubic meters are lost. This is a financial risk, but also a technical one. Defects caused by moisture are manifested, for example, on floors and plasters, often the load-bearing walls and partitions of the building become wet. And if water penetrates for a long time, the damage can be really extensive.

Causes of defects

Pipes often burst due to freezing water in the pipes. When the pipe is backfilled, it may come into contact with stones, which in turn push on the material. The stone can easily damage a piece of pipe. Defects also occur due to mere wear and tear. Conventional pipes used for swimming pools, for example, sometimes seal on the principle of a rubber seal. However, the rubber degrades over time and several leaks can appear on a single route. Faults are also caused by the work done in a hurry (improperly laid pipes, insufficient compaction ...) or non-compliance with work procedures. The subsoil of the pipeline can be flooded in the event of heavy rainfall, which will cause the soil to shift and the faults to be mentioned.

Diversity of localization methods

Whatever the accident, the result is a leak from the pipeline. It is necessary to start finding the place where the defect occurred. There are several methods for this. One of them is acoustic, which is used to detect the fault using audible signals, the distance from the defect of which is determined by the computer. It is also possible to detect the fault location by listening to "fault noise" through the microphone. Another method uses optical mapping with special cameras. Alternatively, the pipeline can be examined using so-called trace gas.

Trace gas wins

During its practice, AKVAHELP METAL conducted an evaluation in which the use of trace gas is the most important detection technology. During the trial period of several years, its technicians did not come into contact with a situation in which this method would fail. It even overshadows the optical method, which surpasses especially in the localization of smaller defects. And how is this type of search performed?

Workflow

Upon arrival at the construction site where the water leak is detected, the plot or building is inspected and project plans are examined (if available). Subsequently, it is necessary to decide which parts of the distribution can be pressurized separately. The second important and difficult step is to design a procedure for closing a given branch, as branches are often terminated by nozzles that do not have a thread. Special sealing bags are used for this, it is necessary to proceed to an individual solution and production of a special seal. Subsequently, it is possible to perform a classic air pressure test, which clarifies the tightness of the branch. If she is successful, other divorces will be approached. But the moment the workers come across leaking pipes, they approach the main working part. The detection gas is let into the branch.

There can be multiple defects in a single branch. At this point, it is time for a very sensitive surface detection sensor (set to a suitable gas concentration), which is manipulated on the surface by a company employee. Without the need to cut or cut, it traces the place (s) where the gas from the pipeline passes into the soil, masonry, etc. At the moment when the branch can not be pressurized at all, it means that the worker encountered damage more). With such a large damage, all the detection gas escapes through this defect, and the gas no longer has a chance to get to any other damage. Therefore, it is necessary to proceed to the immediate repair of this damage and look for further damage after repairing the defect in the given branch. The trace gas is let in again and another defect is sought. This is done all the time until all defects in the specific branch have been located and repaired and the piping has passed the final pressure test.

Sealing the drain from the gutter with a special flow sealing bag for DN up to 300 mm before pressurization

Gas composition

The tracer gas is a mixture of hydrogen (about 5-15%) and nitrogen. Hydrogen, as the lightest element on Earth, has a low viscosity. It is able to penetrate almost any material (except impermeable waterproofing foils, where the material needs to be cut) upwards. In the place of its increased concentration (where the leak in the pipe comes out) it is thus tracked by the mentioned device.

The difficulty is often due to the lack of accurate project plans at the sites of implementation work, and therefore the complex traceability of pipelines. It is thus impossible to copy its route on the surface and look for a gas leak. Workers are often forced to traverse large plots of land here and there with the device in hand, and research takes much more time. It is therefore in the interest of the owner (customer) to know at least the rough location of the pipeline, ideally 2 meters wide, where it is possible to determine the location of the defect effectively with respect to time. Even a five-meter scatter greatly slows down work procedures.

Reliability and efficiency

This is a very effective and reliable method of locating a defect in a pipeline. For example, during the contract in Uničov, AKVAHELP METAL employees found out that they are already the third company that was asked to locate the defect, but which was the first to achieve successful results. Previous companies have not even succeeded with the optical camera method (which, among other things, carries the risk of breaking the pipe as the equipment passes through less penetrating places).

Often, along with the location of the problem, the primary cause of the pipe rupture is clarified. For example, in a children's pool at a swimming pool in Ostrava, where AKAVHELP METAL applied the tracing gas method, a construction error was discovered. The pipe was sloping inappropriately, water remained in it and it froze inside. This allowed the owners to correct the root cause, instead of just removing the consequences.

No side effects

The mixture of hydrogen and nitrogen is completely safe, the proportion of hydrogen is minimal, so there is no risk of explosion, flammability or any toxicity. Of course, safety rules are strictly observed when carrying out the work. There is no waste either. In conclusion, we can also mention a very interesting possibility of repairing the pipeline without the need for mechanical interventions (excavation, uncovering of concreting or backfill ...). Often, the conventional repair method is so expensive that it is better to use this alternative for economic reasons. In this case, AKVAHELP METAL will repair the pipeline using a special liquid with dissolved mineral crystals. It is left in the pipe for about 10 days to circulate. Gradually, the escape points are permanently blocked.

Repaired PVC pipes together with the "replaced" piece.

Conclusion

Metoda lokalizace defektů v potrubí pomocí trasovacího plynu je v současnosti bezkonkurenčně nejpřesnější. Přináší spolehlivé výsledky a rychlý postup. Nemalou výhodou je minimální nutnost mechanických či destrukčních zásahů na stavbě. Důležitý je jistě i výběr dodavatele a jeho zkušenosti. Těmi však třinecká firma AKVAHELP METAL bezpochyby disponuje. Za dlouhé roky, po které tuto metodu využívá zejména jako subdodavatel jiných bazénových společností v rámci servisních služeb, ale také jako dodavatel individuálních provozovatelů objektů či přímo majitelů, nedošlo k jediné neúspěšně zakončené zakázce.

The method of locating defects in the pipeline using trace gas is currently unrivaled. It brings reliable results and fast progress. A significant advantage is the minimal need for mechanical or destructive interventions on the construction site. The choice of supplier and his experience is certainly also important. However, the Třinec-based company AKVAHELP METAL undoubtedly has these at its disposal. For many years, during which he uses this method mainly as a subcontractor of other pool companies in the field of services, but also as a supplier of individual operators of buildings or direct owners, there has not been a single unsuccessfully completed contract.

Trace gas for pipe defect detection
28.01.2020