External leak detection systems employ special equipment not normally connected to the pipeline.
Electrical cable sensors. Cables coated with a specialty chemical are buried directly in the ditch close to the pipeline. When a leak occurs, the hydrocarbons from the leak contact the cables, changing the properties of the chemical coating. This in turn affects the electrical resistance or capacitance of the cable, indicating a leak. Unfortunately, any external hydrocarbon, natural or spilled, will trigger alarms. Also, the sensors generally have to be replaced after an alarm.
Fiber optic sensors. These sensors are also buried in the ditch directly with the pipe. Three different fiber optics technologies exist for detection of leaks. One depends on temperature change caused by escaping liquid or natural gas. The escaping fluid lowers the temperature of the surrounding area and the nearby fiber, indicating a leak.
A second technology depends on the escaping liquid to induce very small curvatures, called microbends, in the fiber. These can be detected and located with an optical time domain reflectometer. One other technique uses chemical changes in the fiber optic cable caused by the presence of hydrocarbons.
Vapor and soil monitoring. These two approaches place leak detection devices in select locations along the pipeline or vapor-gathering tubes along the pipeline. Both monitor the surrounding soil for hydrocarbon vapors caused by leaks. Vapor samples are gathered from the tubes and hoses and analyzed for the presence of hydrocarbon vapors.
Optical. There are active and passive optical methods. Some techniques use either a laser or a broadband device to generate an energy source above the pipeline. Any natural gas particles will absorb or scatter the energy. Sensors detect the absorption or scattering to indicate a leak. Another passive optical technique uses thermal imaging to look for differences in temperature caused by leaks.
New leak detection technologies are constantly emerging, so, once again, this is hardly an exhaustive list.
Conclusion
Clearly, SCADA and leak detection require large investments. The level of commitment to each is motivated by different but overlapping factors. Many SCADA features are productivity items that generate return from more efficient (probably less labor-intensive) operations. They also allow delivery of important commercial information to shippers, suppliers, and customers.
Leak detection has a large element of profitability—reducing lost product, cleanup costs, and associated fines and penalties. It is also imperative for environmental and civic reasons that pipeline companies quickly detect, locate, and respond to leaks of all sizes.
But, as the Bard said, “Therein lies the rub.” Large leaks are relatively easy to detect with current systems and are more damaging than smaller leaks. Smaller leaks are more difficult to detect and require more sensitive and costly leak detection systems. Detecting small leaks quickly before they become large leaks makes intuitive sense. However, the prevailing view, though based on somewhat sketchy information, seems to indicate small leaks either remain small leaks or turn quickly into large leaks. That presents a dilemma to pipeline companies when deciding how much to invest in small leak detection. As a consequence, it is possible some leak detection investment decisions are made just to “take the high ground” morally.
Energy is the essence of life. Every day you decide how you are going to use it by knowing what you want and what it takes to reach that goal, and by maintaining focus. —Oprah Winfrey (1954– )
For pipeline companies, maintenance is about under- standing the condition of the asset. They perform necessary inspections, correct potentially unsafe conditions before they cause failures, and repair failures after they occur. Still, even though maintenance and operations are two different functions, the same people often perform them.
Pipeline maintenance has evolved over time. It started out as “fixing components when they break,” just as a driver changes a tire when it blows out. As technology improved, the industry began to appreciate the value of avoiding failures and their associated costs. Public expectations heightened. The definition of maintenance broadened to include preventive maintenance—replacing components before they break— based on the average life expectancy and visual inspections of components. Similarly, more attentive drivers change their tires when they look worn or the tread depth is below a certain level, but certainly before the tire experiences a blowout.
Maintenance
Nowadays, the concept of maintenance in the pipeline industry also includes predictive maintenance. This goes beyond maintenance based only on component life expectancy and elementary inspections. Maintenance plans now use sophisticated data collection and interpretation technologies to prioritize maintenance activities. Pipeline companies, just like car owners, rely on com- puterized analysis to determine what is happening “under the hood.”
Pipeline assets can conveniently be divided into the components inside the pump stations, compressor stations, and meter stations, and those out- side. Equipment inside the stations is maintained much like equipment in manufacturing plants. Other books cover the topic of maintaining plant equipment. This chapter focuses only on maintaining pipelines outside the station. It covers releases, what causes them, how to prevent them, and how to find potential problems before they become failures. It also discusses how to allocate resources to repair the most critical potential problems, and finally, how to repair problems if they occur.