Leak detection
As a means of long-distance transport, pipelines have to fulfill high demands of safety, reliability and efficiency.
[1] If a pipeline is not properly maintained, it can corrode, particularly at construction joints, low points where moisture collects, or locations with imperfections in the pipe.
[1] The most common leak detection method for pipeline operators is called the Supervisory Control And Data Acquisition (SCADA) system.
This system uses a series of sensors to track data such as pressure, flow rates, temperature, and whether valves are open or closed.
The sensors relay the information to a control room where operators determine the legitimacy of the leak alarms.
This recommended practice (RP)[3] focuses on the design, implementation, testing and operation of LDS that use an algorithmic approach.
[3] System cost and complexity of internally based LDS are moderate because they use existing field instrumentation.
When a pipeline wall breakdown occurs, fluid or gas escapes in the form of a high velocity jet.
The operating principles of the method are based on the very important characteristic of pressure waves to travel over long distances at the speed of sound guided by the pipeline walls.
A complex mathematical algorithm analyzes data from pressure sensors and is able in a matter of seconds to point to the location of the leakage with accuracy less than 50 m (164 ft).
[7] Enhanced balancing methods additionally take into account the change rate of the mass inventory of the pipeline.
[3] These methods are based on state observers which are designed from fluid mathematical models expressed in state-space representation.
A common approach is the use of the hypothesis test procedure This is a classical detection problem, and there are various solutions known from statistics.
An RTTM makes it possible to calculate mass flow, pressure, density and temperature at every point along the pipeline in real-time with the help of mathematical algorithms.
[16] E-RTTM[6][7] stands for "Extended Real-Time Transient Model", using RTTM technology with statistical methods.
So, leak detection is possible during steady-state and transient condition with high sensitivity, and false alarms will be avoided using statistical methods.
[19] High quality thermographic technology accurately measures and visualizes emissivity or infrared radiation (thermal heat) of objects into gray scale imagery without the need for ambient lighting.
The addition of an analytic software component, typically optimizable to better address a specific application or environment, enables automated onsite leak analysis, validation and reporting, thereby reducing reliance on man power.
A leak appearing within an analytic region (a rule added to the camera) is immediately analyzed for its attributes, including thermal temperature, size, and behaviour (e.g. spraying, pooling, spilling).
The system's layers of filters and immunity to environmental elements, such as snow, ice, rain, fog and glare, contribute to false alarms reduction.
An electrical signal is passed through the internal conductors and is monitored by an inbuilt microprocessor inside the cable connector.
Escaping fluids pass through the external permeable braid and make contact with the internal semi-permeable conductors.
The microprocessor can locate the fluid to within a 1-metre resolution along its length and provide an appropriate signal to monitoring systems or operators.
A high-resolution infrared radiometer allows entire areas to be scanned and the resulting data to be displayed as pictures with areas of differing temperatures designated by differing grey tones on a black & white image or by various colours on a colour image.
An escaping pressurized water jet underground can create a faint noise which will be muffled on its way to the surface.
If a leak occurs, the substances to be measured come into contact with the tube in the form of vapour, gas or dissolved in water.
In addition, the distributed fibre-optical temperature-sensing technique offers the possibility to measure temperature along the pipeline.
[6][27] The DAS method involves a similar installation of fiber-optic cable along the length of pipeline being monitored.
Larger spills will typically be identified by a "sheen" in wetland or an area of dead vegetation around the release location.
Biological methods of leak detection includes the use of dogs, which are more likely to be used once a release has been identified but not located due to its small size; or by landscapers who keep the pipeline right of way clear.
