Like any other industrial equipment, pipelines require regular maintenance to maintain optimal functionality. With exposure to both internal and external conditions, pipelines can undergo corrosive damage leading to contaminant buildup, structural damage, and product contamination. Regularly scheduled cleaning activities can be used to prolong the useful lifespan of pipelines.
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Maintaining industrial pipelines is critical to production operations for several reasons. To begin with, oil and gas pipelines are susceptible to wear over time, exposing them to moisture and chemical attacks. Unchecked oxidative processes will result in pipeline corrosion and the buildup of deposits within the pipeline channels. This will result in damage to the structural integrity as well as contamination of products being conveyed by the pipelines.
Regular pipeline cleaning will identify points of concern, eliminate buildup within the channels as well as inhibit negative oxidative reactions, and prolonging pipeline durability. Perhaps more importantly, routine pipeline cleaning should be an integral part of the industrial safety checklist to ensure occupational health and safety risks to personnel are as minimal as possible.
Having established the usefulness of industrial process pipeline cleaning, it is equally important to know when to implement pipeline cleaning solutions. There are various points in the lifetime of a pipeline where pipeline cleaning solutions must be applied.
Among the critical phases of pipeline operation where cleaning should be done include:
The above-mentioned scenarios mandate pipeline cleaning to ensure the safety of all persons involved in the pipeline operation. Further, careful maintenance will ensure compliance with environmental safety regulations.
Outlined below are six effective pipeline cleaning techniques available to industrial pipeline operators:
The various ways to achieve mechanical and chemical cleaning for oil and gas pipelines are described in the subsequent sections of this article.
Mechanical clearance of buildup within gas channels is done using pipeline cleaning pigs. Pipe cleaning pigging systems come in various configurations, including gel and utility pigs.
Gel pigs are a popular choice for operators in moisture and debris removal, as well as pipeline dewatering and drying processes. Gel pigs are designed for use in pipelines categorized as “unpiggable” with difficult to navigate bends and poor/absent launch and retrieval hardware.
Additional benefits of using gel pigs include:
Utility pigs are used in conventional pipe cleaning operations to achieve mechanical clearance of solid contaminants, water vapor, and debris. Utility pigs can also be used in pipeline proving operations to determine the nature of buildup within the affected pipelines and guide the approach to clearance. These pigs, however, require standard launch and retrieval hardware to function properly.
Examples of utility pigs include:
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Pipe cleaning can also be achieved using chemical means, including purging with nitrogen gas and other specialty flushing solutions.
Pipeline purging with gaseous nitrogen can be used to eliminate various types of contaminants, including oxygen, corrosion particles, and moisture. Forcing a stream of nitrogen gas through the pipeline will drive out these impurities. As an added benefit, the inert nature of nitrogen will help stabilize the internal environment of the pipeline reducing the likelihood of combustive events occurring.
This technique is a combination of chemical flushing and mechanical pigging. Mixing liquid cleaning solutions with diluents like water, isopropyl alcohol, diesel, or methanol, will produce an effective pipe cleaning solution. This specialty solution can be driven by mechanical pigs through a pipeline to clear buildups of particulate impurities. When constituting the cleaning fluid, operators must consider the following:
Regardless of the type of pipeline targeted for maintenance, there are general ways by which pipe clearance can be achieved. Some universal pipe cleaning guidelines are outlined below:
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Construction of pipelines involves route survey, ditching or trenching, transporting the pipes, fittings, and other materials to the site, stringing the pipes along the ditch, bending steel pipes in the field to suit local topography, applying coating and wrapping to steel pipes, joining pipes together either before or after they are lowered into the trench (this depends on the type of pipes used), checking for possible welding flaws or leakage at the joints, and then covering trenches by soil and restoration of the land to its original appearance. For long pipelines, construction is done in segments so that one segment of the pipeline is completed before construction proceeds to the next. This minimizes the time that any given place is disturbed by construction activities. Even for large pipelines, construction for any segment is usually completed within six months and often in much less time. Small pipelines can be constructed in days.
When a pipeline must cross a river or creek, the pipe can be either attached a to a bridge, laid on the streambed underwater, or bored through the ground underneath the river. Modern boring machines allow convenient pipeline crossing of rivers and roads.
The safety of pipelines depends to a large extent on the materials transported. Pipelines that transport water or use water to transport coarse solids, such as hydraulic capsule pipelines, do not explode or pollute the environment in the event of pipe rupture or spill. They pose few safety or environmental hazards. Crude-oil pipelines, when ruptured, do not explode but may pollute waters and soil. Natural gas pipelines and product pipelines that contain highly volatile liquids such as gasoline may explode in a spill; they deserve the greatest safety considerations. Even in this case, however, it is generally accepted that the safest way to transport petroleum and natural gas is by pipeline. To use other modes such as truck or railroad to transport such fuel would be far more dangerous and costly.
Even though pipelines have the best safety record of all transportation modes, in the United States pipeline safety is still a major concern of the government and the public owing to occasional spills and accidents. As a result, a major emphasis of pipeline operations in the United States is safety. Many measures are taken to prevent and detect ruptures and leaks and to correct problems whenever they occur.
In the United States about half of all pipeline accidents are caused by a third party, as, for instance, a builder damaging a pipe while digging the foundation of a house. Consequently, pipeline companies make special efforts to educate the public about pipeline safety and inform cities and construction groups about the locations of underground pipelines in order to reduce third-party damage.
The second leading cause of pipeline failure is corrosion, which is an electrochemical process caused by the contact of metal pipe with wet soil (external corrosion) and with the fluid in the pipe if the fluid is corrosive or contains water with dissolved oxygen, carbon dioxide, or hydrogen sulfide (internal corrosion). Pipeline companies take many measures to prevent corrosion, such as covering underground pipelines with tape and using cathodic protection against external corrosion and adding special chemicals (corrosion inhibitants) to the fluid to prevent internal corrosion. Hydrazine (N2H4) and sodium sulfite (Na2SO3) are two chemicals commonly used to control internal corrosion of metal pipes that carry water. The chemicals reduce corrosion by reacting with and hence removing the dissolved oxygen in water.
Finally, detection of leaks is done by computer monitoring of abnormal flow rates and pressure and by flying aircraft along pipelines for visual inspection. Special “pigs” are also sent through pipelines to detect possible flaws of the pipeline walls and signs of corrosion. Highly corroded pipes are replaced before a leak develops. Often referred to as “smart pigs,” these carry instruments that detect cracks and corrosion of pipeline interiors.
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Henry Liu