Faster Safety Inspection of Natural Gas Pipes

Bar hole drilling has been reduced by half at Gasnätet Stockholm, since the utility started using the INFICON IRwin® infrared gas detector last year.

Previously, a small team was required to arrive on-site to drill through the road surfacing material and take samples whenever a gas leak was suspected.

Now, the position of a gas leak is verified by the same person identifying the leak, using a unique vacuum bell to draw gas through the road surface without drilling holes.

The operator walks the route of the network, using a gas sampling device under a rubber carpet supported by wheels. When gas is found, the tool at the end of the sampling hose is changed from a carpet probe to a vacuum bell.

The vacuum bell is pressed against the surface to form an airtight seal. A pump in the instrument draws air through the road surface and into the detector. Once a steady flow is established, the true concentration of gas can be determined. The whole procedure takes 10-20 seconds, much faster than drilling a hole in the pavement.

"When I first saw the vacuum bell, I must admit I was very skeptical," says Robin Kronesäter, operations manager at Gasnätet Stockholm.

"I didn't think it would work. So during a training course, where we were learning how to use the instrument, I took the group and the instructor to a place where I knew there was a small gas leak. I was very surprised when the instructor was able to pinpoint the location straight away. The leak was just below the spot he pointed out. Now, I'm a great supporter of using the vacuum bell."

As excavation work is costly, Gasnätet Stockholm focuses on preventive maintenance of its network, aiming to eliminate small problems before they escalate. Every summer, the company hires seasonal workers, mainly students on their summer break, to survey the network. Last year, the company replaced the semiconductor instruments it had previously used, with infrared IRwin detectors from INFICON.

The field workers pinpoint any leaks they find in the company's mapping system. When summer is over, all reports are followed up by repair teams.

"Our seasonal workers walk the route of the network, using IRwin with the carpet. This works well. They find gas and we get very few questions from them. The instrument is self-explanatory," says Robin Kronesäter.

"We still need to drill some of the time. For instance, in the winter, the ground is frozen and then it isn't possible to draw gas through the road surface. But most of the time, we can rely on the vacuum bell to deliver accurate results."

The instrument is easy for one person to carry. With the built-in GPS tracking system, it does not require a second operator to handle the documentation.

The pump in the IRwin unit quickly draws gas, using the bell probe, through all types of surfaces, including tarmac and concrete. The infrared sensor gives a rapid response if any gas is present, which prompts the operator to stop and make further tests. This includes pinpointing the exact location by finding the point of maximum concentration.

Gas is becoming increasingly popular in the Stockholm area, particularly with the restaurant trade, where it is used for cooking and also as a fuel for patio heaters. With heaters, restaurants can extend their outdoor season by two months in the autumn and two months in the spring. Gas heaters are more efficient than electrical ones and their output is not limited by the capacity of the electricity supply.

The gas in Stockholm's gas network is a mix of natural gas and biogas. As much as 70% is biogas, produced from processing of food waste and from sewage treatment.

"So in a small way we help Stockholm's restaurants be more sustainable, by converting biogas from for example food waste into heating for their outdoor areas and gas on their stoves," says Robin Kronesäter.

For more information on how IRwin can help make pipeline surveying easier for you, contact us at reachus@inficon.com.