Delivery Pipelines are the most important component of a natural gas distribution system. Over the past few years, the demand of natural gas has increased rapidly, and at a same time the distribution system infrastructure has been aging with time. Thus, natural gas pipelines are often susceptible to leakage. Since natural gas is transported to long distances, it is important to have robust leak detection techniques in place. CGD companies in India conduct regular Leak Detection Test to check for leakages in pipelines.
Pipeline leak detection methods can be classified into various categories such as Non-technical methods, Hardware based methods, Optical & Non-optical methods, Software based methods etc.
- Visual Inspection & Non-Technical Methods
- The most common method used for leak detection is visual inspection. Although this method is not accurate & reliable, it is the preliminary check for detection of leakages in pipelines.
- Other Non-technical method which are in use are use of Dogs & use of soap bubble solution. Trained Sniffer dogs are used across the world for detecting leaks. A trained dog can locate & pin-point small quantities of gas of a magnitude as low as 0.07 ml, which is usually undetectable by conventional methods. The dog can detect gas escaping from pipelines buried up to 31 inches below the surface, & are capable to inspect up to 5 km of pipeline per day. However, the effectiveness of this method is dependent upon the fatigue level of dog and the person handling the dog. Soap solution is very widely used for detecting leaks in India. Various CGD companies use soap solutions to pin-point leaks at joints and valves. This technique helps in localization of leaks, but is only applicable to pipelines which are easily accessible.
2. Hardware Based Methods
- Special sensing devices handled by trained personnel are used for detecting gas leakage. These methods are also referred to as External methods. Leak finder devices are used widely in India. Sensing methods can be of various types such as fibre optics, acoustic, gas & soil sampling, flow meters etc.
- Optical methods are widely used for leak detection and can be divided in two categories viz. passive & active. The active methods require illuminating the scanned area using a radiation source while passive methods do not require a source and rely only on background radiation or the radiation emitted by the gas.
- Various types of passive leak detection systems in use are thermal imaging, multi-spectral imaging and gas filter correlation radiometry.
- Active method such as Light detection & Ranging (LIDAR), diode laser absorption, millimetre wave radar systems, backscatter imaging, broad band absorption and optical fibre are also in use.
- Acoustic methods use acoustic emission sensors to detect leaks. When gas leaks from a pipeline, it generates a signal (acoustic) at the location of leak. The sensors then analyse the changes in the background noise pattern and thus detect leaks.
- Flame ionization detectors are widely used in India for detection of methane or ethane. This method is quite accurate but not reliable for very long distances.
- Tracer based leak detection methods are also used, where a small amount of tracer is injected in the pipeline. As leakage starts, the tracer leaks along with the gas and the change in background of soil can be easily detected. This method can only be used for buried pipelines and it expensive due to continuous addition of tracer.
- Other hardware based methods in use are flow monitoring devices that measure the change in pressure & flow rate in various segments of a pipeline, thereby detecting a potential leak. The biggest advantage of this method is that, it does not interfere with pipe operation.
3. Software based Methods
- Software based dynamic modelling is a popular technique in use now-a-days. The variation in various flow parameters such as temperature, pressure, flow etc. at different locations along the pipeline is monitored & analysed through a mathematical model.
- Negative pressure wave & Pressure point analysis are robust methods which analyse the change in pressure of an operating pipeline, which indicates leakage.