Identifying Leaks from Natural Gas pipelines at a Safe Distance

The use of natural gas, of which methane is the principle component, is increasing worldwide. It also has many industrial uses, such as the manufacture of chemicals like ammonia, methanol, butane, ethane, propane and acetic acid; it is also an ingredient in products as diverse as fertilizer, antifreeze, plastics, pharmaceuticals and fabrics.

Natural gas is transported in several ways: through pipelines in gaseous form; as liquefied natural gas (LNG) or compressed natural gas (CNG). LNG is the normal method for transporting the gas over very long distances, such as across oceans, while CNG is usually carried by tanker trucks over short distances. Pipelines are the preferred transport choice for long distances over land (and sometimes offshore), such as between Russia and central Europe. Local distribution companies also deliver natural gas to commercial and domestic users across utility networks within countries, regions and municipalities.

Regular maintenance of gas distribution systems is essential. Identifying and rectifying gas leaks is also an integral part of any maintenance programme, but it is notoriously difficult in many urban and industrial environments, as the gas pipes may be located underground, overhead, in ceilings, behind walls and bulkheads or in otherwise inaccessible locations such as locked buildings. Until recently, suspected leaks from these pipelines could lead to whole areas being cordoned off until the location of the leak was found.

Precisely because conventional gas detectors – such as those utilising catalytic combustion, flame ionisation or semiconductor technology – are not capable of remote gas detection and are therefore unable to detect gas leaks in hard to access pipelines, there has been a lot of recent research into ways of detecting methane gas remotely.

Remote Detection

Cutting edge technologies are now becoming available which allow the remote detection and identification of leaks with pinpoint accuracy. Hand-held units, for example, can now detect methane at distances of up to 100 metres, while aircraft-mounted systems can identify leaks half a kilometre away. These new technologies are transforming the way natural gas leaks are detected and dealt with.

Remote sensing is achieved using infrared laser absorption spectroscopy. Because methane absorbs a specific wavelength of infrared light, these instruments emit infrared lasers. The laser beam is directed to wherever the leak is suspected, such as a gas pipe or a ceiling. Because some of the light is absorbed by the methane, the light received back provides a measurement of absorption by the gas. A useful feature of these systems is the fact that the laser beam can penetrate transparent surfaces, such as glass or perspex, so it may be possible to test an enclosed space prior to entering it. The detectors measure the average methane gas density between the detector and target. Readings on the handheld units are given in ppm-m (a product of the concentration of methane cloud (ppm) and path length (m)). In this way, methane leaks can be quickly confirmed by pointing a laser beam towards the suspected leak or along a survey line, for example.

An important difference between the new technology and conventional methane detectors is that the new systems measure average methane concentration, rather than detecting methane at a single point – this gives a more accurate indication of the severity of the leak.

Applications for hand-held devices include:

  • Pipeline surveys
  • Gas plant
  • Industrial and commercial property surveys
  • Emergency call out
  • Landfill gas monitoring
  • Road surface survey

Municipal Distribution Networks

The benefits of remote technology for monitoring pipelines in urban settings are now being realised.

The ability of remote detection devices to monitor gas leaks from a distance makes them extremely useful tools in emergencies. Operators can stay away from potentially dangerous leak sources when checking the presence of gas in closed premises or confined spaces as the technology allows them to monitor the situation without actually gaining access. Not only is this process easier and quicker, but it is also safe. Moreover, it is not affected by other gases present in the atmosphere since the detectors are calibrated to only detect methane – therefore there is no danger of getting false signals, which is important in emergency situations.

The principle of remote detection is also applied when inspecting risers (the above-ground pipes carrying gas to the customers’ premises and normally running along the building outside walls). In this case, the operators point the device towards the pipe, following its route; they can do this from ground level, without having to use ladders or access the customers’ properties.

Hazardous Areas

In addition to detecting gas leaks from municipal distribution networks, explosion-proof, ATEX approved devices can be used in Zone 1 hazardous areas such as petrochemical plants, oil refineries, LNG terminals and vessels, as well as certain mining applications.

When inspecting an LNG/LPG underground tank, for example, an explosion-proof device would be required within 7.5 metres of the tank itself and one metre around the safety valve. Operators therefore need to be fully aware of these restrictions and equipped with the appropriate equipment type.

GPS Coordination

Some instruments now allow spot methane readings to be taken at various points around a site – such as an LNG terminal – automatically generating GPS tracking of the measurement readings and locations. This makes return trips for additional investigations far more efficient, while also providing a bona-fide record of confirmed inspection activity – often a prerequisite for regulatory compliance.

Aerial Detection

Moving beyond hand-held devices, there are also remote methane detectors which can be fitted to aircraft and which detect leaks from gas pipelines over hundreds of kilometres. These systems can detect methane levels at concentrations as small as 0.5ppm up to 500 metres away and include a real-time moving map display of gas concentrations as the survey is conducted.

The way these systems work is relatively simple. A remote detector is attached beneath the aircraft’s fuselage (usually a helicopter). As with the handheld device, the unit produces an infrared laser signal, which is deflected by any methane leakage within its path; higher methane levels result in more beam deflection. These systems also utilise GPS, so the pilot can follow a real-time moving map GPS route display of the pipeline, with a real-time display of aircraft path, gas leaks and concentration (in ppm) presented to the crew at all times. An audible alarm can be set for a desired gas concentration, allowing the pilot to approach for closer investigation.

Conclusion

The range of remote methane detection systems is increasing rapidly, with new technologies being developed all the time. All these devices, whether hand-held or fitted to aircraft, allow quick, safe and highly targeted identification of leaks – whether beneath the pavement, in a city or across hundreds of kilometres of Alaskan tundra. This not only helps prevent wasteful and costly emissions – it also ensures personnel working on or near the pipelines are not exposed to unnecessary danger.

Because the use of natural gas is increasing worldwide we foresee rapid technological advances in remote gas detection in applications as diverse as leak survey, transmission integrity, plant and facilities management, agriculture and waste management, as well as process engineering applications such as coke and steel production. Each of these areas have situations where access may be difficult, combined with the need to put personnel protection at the top of the agenda. Opportunities for remote methane detectors are therefore growing all the time.

 

Explosion hazards in inerted tanks and how to avoid them

Hydrogen sulphide (H2S) is known for being extremely toxic, as well as highly corrosive. In an inerted tank environment, it poses an additional and serious hazard combustion which, it is suspected, has been the cause of serious explosions in the past.

Hydrogen sulphide can be present in %vol levels in “sour” oil or gas. Fuel can also be turned ‘sour’ by the action of sulphate-reducing bacteria found in sea water, often present in cargo holds of tankers. It is therefore important to continue to monitor the level of H2S, as it can change, particularly at sea. This H2S can increase the likelihood of a fire if the situation is not properly managed.

Tanks are generally lined with iron (sometimes zinc-coated). Iron rusts, creating iron oxide (FeO). In an inerted headspace of a tank, iron oxide can react with H2S to form iron sulphide (FeS). Iron sulphide is a pyrophore; which means that it can spontaneously ignite in the presence of oxygen

Excluding the elements of fire

A tank full of oil or gas is an obvious fire hazard under the right circumstances. The three elements of fire are fuel, oxygen and an ignition source. Without these three things, a fire can’t start. Air is around 21% oxygen. Therefore, a common means to control the risk of a fire in a tank is to remove as much air as possible by flushing the air out of the tank with an inert gas, such as nitrogen or carbon dioxide. During tank unloading, care is taken that fuel is replaced with inert gas rather than air. This removes the oxygen and prevents fire starting.

By definition, there is not enough oxygen in an inerted environment for a fire to start. But at some point, air will have to be let into the tank – for maintenance staff to safety enter, for example. There is now the chance for the three elements of fire coming together. How is it to be controlled?

  • Oxygen has to be allowed in
  • There may be present FeS, which the oxygen will cause to spark
  • The element that can be controlled is fuel.

If all the fuel has been removed and the combination of air and FeS causes a spark, it can’t do any harm.

Monitoring the elements

From the above, it is obvious how important it is to keep track of all the elements that could cause a fire in these fuel tanks. Oxygen and fuel can be directly monitored using an appropriate gas detector, like Gas-Pro TK. Designed for these specialist environments, Gas-Pro TK automatically copes with measuring a tank full of gas (measured in %vol) and a tank nearly empty of gas (measured in %LEL). Gas-Pro TK can tell you when oxygen levels are low enough to be safe to load fuel or high enough for staff to safely enter the tank. Another important use for Gas-Pro TK is to monitor for H2S, to allow you judge the likely presence of the pryophore, iron sulphide.

Servicing for safety… A visit to the oil refinery

Working in the office makes it easy to focus on the individual tasks and get detached from how our products are making a difference to people’s lives. One of our customers was kind enough to facilitate an onsite visit so that Andrea (our Halma Future Leader on a marketing placement) could see first-hand how our products are used and who the end users are. This meant a visit to an oil refinery to see where our Crowcon portable gas detectors are used.


“The main thing that surprised me was the sheer size of the site. The oil refinery was very spaced out and it took us 10 minutes to walk from the entrance of the site to where the Crowcon engineer’s based. The engineers and employees around different parts of the refinery wore Hi Vis jackets, big safety boots, hard hats and all appeared to have personal gas detectors. During a quick site tour, I learned the products of the oil refinery are not limited to gas or petrol, but also tar, asphalt, lubricants, washing up liquid, paraffin wax and much more.

The products are all stored in big containers with pipes all over the site. Most of the products are highly flammable which explains the big focus on safety. In the distance, there were a few dome shaped containers which are pressurised vessels. If one of them were to explode, it would have a 10 mile blast radius. Suddenly I had the urge to leave and drive about 10 miles.

Crowcon’s engineer base was full of orange T4s, Gas-Pros as well as an army of “Daleks”, I mean Detectives, awaiting calibration and service. While the harshness of this industrial environment was evident from their appearance, they were otherwise in good working order, and the service engineer worked through the devices quickly.

The end users think of them as a simple device they have to wear to do their job, and they like the simplicity and reliability of Crowcon devices. The Detectives get thrown around and Gas-Pros are almost black is comparison to the usual orange, which just showcases how important the robustness of our devices is. The dangers of this working environment are not generally a big concern to the users, this is everyday life to them. Our devices help ensure they go home after a tough shift. Ensuring the devices are functioning properly is down to the service engineers, and they need to think for the users to ensure that the devices are being used properly.

Seeing Crowcon’s devices being used and the number of times someone enquired if the devices are calibrated and ready to go back into action, highlighted just how important use of portables as part of the safety regime  is considered. “Quality” and “robust” is how users describe Crowcon products and even though they may now treat them like the life saving devices they are, the devices are regularly used and valued. They make a very flammable and dangerous environment a safer place to be.”

Facts on Fixed Detection

Optimal placement of fixed gas detectors requires thorough risk assessment. This short video highlights some of the questions you need to ask before buying or installing a fixed system at your plant or site.

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The simple steps to looking after your gas detection equipment this winter.

Gas detectors are there to save your life, whether it is a fixed system or a portable detector, keeping them well maintained is an important part of ownership.

Our guest blogger this week, Julian, has put together simple steps to ensure your gas detector is up for the job as and when it’s required.

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Hydrogen Sulphide: toxic and deadly – Chris explains more about this dangerous gas

Many of you will have come across hydrogen sulphide (H2S). If you have ever cracked a rotten egg the distinctive smell is H2S.

H2S is a hazardous gas that is found in many work environments, and even at low concentrations it is toxic. It can be a product of man-made process or a by-product of natural decomposition. From offshore oil production to sewerage works, petrochemical plants to farms and fishing vessels, H2S presents a real hazard to workers.

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Why do we calibrate?

I’ve talked about bump testing your instrument, so it seems natural that we now cover the importance of calibrating.

There are two main reasons for calibration. Firstly, gas detectors often operate in harsh environments: high and low temperatures and/or humidities; they may be exposed to contaminants, such as solvents, silicone etc; gas exposure; as well as the age of a sensor; any of which can result in the degree to which the detector responds to a given gas concentration changing, for example, the detector may read 46% LEL when the true level is 50% LEL.

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