Barney's Blog no 3 - Urban Gas Pipeline Defects and Gas Leaks

Moscow is a city of extremes; hot summers and cold winters means that utility pipes for water and gas are buried deeper than in more temperate climates to avoid extreme temperature changes.

 

Much of the housing in city and suburbs are large apartment blocks built in a hurry after the war, marginally improved now, and each housing maybe 4-5000 people.
To provide heat in cold winters, generally district heating systems are installed; They may use the waste heat from power stations to superheat water pumped around a primary network to the secondary heating station that serves several apartment blocks with central heating and hot water.
Alternatively, if no power station is nearby, a very large gas boiler will be used to provide central heating and hot water for a group of 5 or 6 apartment blocks. This is the system adopted in the suburbs of Moscow. There is also a sizeable gas feed into each apartment block for cooking.

Russia has profited from exporting much of its production from its huge natural gas reserves, and Gazprom finally has directed funds to be spent on maintenance of the urban and suburban gas networks, necessary after several gas explosions in or near apartment blocks due to gas leaks.

So suburban and regional gas companies needed a technique to pinpoint possible leak positions on their tar coated steel pipelines. Generally plastic gas pipes are not used as supply pipes to apartment blocks and only sometimes to single houses.

The methods for long distance transmission pipelines were not so successful on shorter urban pipelines. The "intensive method" required an operational cathodic protection station, and these sometimes were not working because electricity supply had failed, broken cathodic protection cables to pipeline or general neglect. Measuring the current on the pipelines, worked to some degree, but would not see small current loss faults that needed to be found unless used with A frame for measuring AC voltage gradient as the fault was approached and passed.

Seba KMT and Vivax Metrotech have a powerful low frequency transmitter, FLG 50, powered from internal batteries, external 12V (car battery) supply and mains, and this usually operated with the Seba FLE 10 system, but was adapted to work with the Metrotech i-5000 locator. Also a new development, using Signal Select directional indication with a new A frame provided very quick direction to fault. It proved successful.

The Transmitter FLG50 was connected at the cathodic protection station to the anode and cable to pipeline. With the Signal Select directional 491Hz low frequency and plenty of current up to 3Amps, the locator could first confirm that the CP was connected to the Anode and Pipeline correctly, and then the operator could start looking for faults.

Sometimes we were surprised to discover that the Anode and Pipeline connections were proved to be connected in reverse, so no doubt this added to corrosion problems.

Using the i-5000 locator and A frame allowed speedy pinpointing of even the smallest faults, by using the simple "+" forward or "–" backward direction to fault provided by the Signal Select direction method, and the intensity of the signal to precisely pinpoint the fault.

Then the gas company hammered in a bar-holing bar because of the pipe depth to create a hole above the pipeline and insert a gas detector into the hole to sniff for gas; if gas was detected they dug down to expose the pipe and repair the problem. If no gas was detected no action was immediately necessary apart to repair the coating defect.

During one of our tests we located the steel pipeline feeding the apartment block that passed just 2 Metres from a children's play area. The children were having a fine time on the swings; the parents were sitting on the benches in the sunshine having a cigarette. We found a fault just by the benches and it also proved to be a small gas leak...

The sensitivity of the i-5000 system was such that sometimes it could also find the points where the steel pipeline sections were welded and joined together. These were also sometimes gas leaks.
Anyway the suburban gas company technicians were very impressed by the results because
this whole operational system speeded up the previous method that used bar-holing at regular intervals a rather hit and miss operation.
It was made simpler for the operator by installing Russian Language Menu into the operating software of the i-5000 locator.

Long distance gas and oil transmission pipelines

Generally the long distance gas and oil transmission pipelines that run thousands of kilometres across Russia carrying product out of Siberia to Europe and through to China are well inspected by teams of engineers and surveyors and the Cathodic protection systems have maintained because of the high value of the gas and oil exported and its export earnings for Gasprom and various oil companies. But the suburban and urban systems were considered less important until there were casualties from gas explosions and the authorities were compelled to make repairs.

The intensive method for finding coating defects is frequently used, it requires good contact with the ground and it is accurate but rather slow to use, with maybe only 4 KM per day as possible measurement distance. It is terrain dependent due to trailing wire back to Cathodic Protection Station and practical difficulties at river crossings.

The Pipeline Current Measurement method that measures the current gradient at regular distances to quickly find the greatest current losses, is far quicker and permits greater distances to be covered perhaps as much as 15 KM per day, or double if 2 receivers are used in opposite directions from the same transmitter.

Vivax Metrotech produce the new Vloc Defect Mapper location system. There is a powerful 150Watt transmitter, powered by mains, 12V car battery or output from cathodic protection station. The Vloc DM locator has built in datalogging and Bluetooth and GPS for long distance pipelines and easy to understand colour LCD display.

This locator has internal software to present the graph of current loss against distance travelled, and a "walkback" system to allow the operator to return to points of interest, perhaps to use a fault pinpointing A frame, at the position of the cursor on the screen.

This new development is useful for security, so the Engineer/Surveyor does not have to mark the ground during the survey, marking the pipe position and making it easy to find for potential product thieves.

The operator can stop where the current graph begins to fall, attach the A frame and search the fault, save the small extra graph and its position for future repairs.

During the survey data can be transferred via Bluetooth interface to external datalogger or GPS system. Also at the end of the survey the data collected can be loaded into a mapping system, and generally clicking on the measuring point displays the result at the particular point. It is particularly useful if Google earth is used, as the pipe route is laid across the surface with the measuring points simply displayed.

The Vloc DM system also stores 1000 logs for later downloading to propretry PC software or Vivax own system, "vMapper Pro".

Email barney@mansls.co.uk for more info on this subject.