Technology of Pipelines – Industry R&DThe evolution of pipeline technology parallels advancements in pipeline safety and involves improvements to just about every aspect of pipelines.
Materials –The earliest crude oil and natural gas pipelines in North America were made either of wrought iron or cast iron. Wrought iron is almost pure iron and cast iron has a high carbon content. Both of these materials are weaker and more brittle than steel pipe. Steel pipe was introduced in the latter half of the 19th century and by 1900, was the primary pipe material. It is still 98 to 99 percent iron, but also contains 0.001 to 0.30 percent by weight carbon and 0.3 to 1.5 per cent by weight manganese, and may contain trace amounts of columbium, molybdenum, vanadium and titanium depending upon end use. All of these alloying materials add strength, toughness, ductility and weldability.
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Pipe Making – Pipe is made by forming hollow cylinders from flat sheets of steel and welding the lateral edges together. Early processes, called furnace welding, involved drawing red-hot steel through a tapered form which forced the lateral edges of the sheet together creating the circular cross section and sealing the seam. Seams formed in this manner had a burst strength on the order of only 70 per cent of that of the steel.
The first improvement on this method was to taper the lateral edges to increase the surface area of the weld, which improved the burst strength to 90 per cent of that of the pipe material.
Electric welding allowed the steel sheets to be formed into tubes at much lower temperatures. As the lateral edges were forced together, an electric current was applied to heat only the weld area and bond the edges together. Using this process, the strength of such seams exceeded that of the pipe material.
Seamless pipe was made by rolling solid round “billets” into ovals. As the core of the oval began to fail, a round mandrill was longitudinally forced through the billet, creating a round tube.
In the mid 1940s, arc welding, where the edges are joined by an electric arc between the pipe material and an electrode of filler metal, was introduced to pipe making. Initially, the seams were welded only from the outside surface, but by the late 1940s, welds were made on both the inside and outside surfaces of the pipe.
Since the 1950s, stronger grades of steel have been introduced, as well as improved welding, inspection and quality control practices.
Pipe Joining – Pipe sections in early pipelines were joined together using screwed collars, but as pipe diameter and operating pressures increased, other means such as bolted flanges, were implemented. Another method involved using rings to hold packing seals in place.
Acetylene welding was first used around 1911 to join pipe segments together (girth welding) and just prior to 1920, arc welding was introduced. Initially, welding techniques required the pipe be rolled as the welds were made. Later advances made it possible to weld in an overhead position.
From the late 1940s, radiography was used to inspect welds. Since then other methods such as magnetic particle inspection and ultrasonic inspection have been developed and implemented.
Corrosion Control – Steel pipe is subject to corrosion when buried in soil, so early pipelines were coated in tar or asphalt as they were being installed. Later advances included epoxy and polyethylene coatings applied at the manufacturing plant.
Following the discovery of corrosion as an electro-chemical process, cathodic protection was introduced. Cathodic protection involves applying a weak direct current of electricity to the pipeline to prevent corrosion. The current flows into the pipe through breaks in the outer coating and protects the bare metal from water and other corrosive agents.
Maintenance – To ensure the integrity and safety of their pipelines pipeline operators monitor their pipelines 24 hours per day, seven days per week from central control centres and use aircraft to visually inspect their right-of-ways looking for signs of leaks.
Maintenance programs include scheduled inspections of valves and other components, regular pipeline integrity testing and regular inspections of crossings.
Pipelines are cleaned internally by bullet-shaped devices known as “pigs” because of the squealing noise they make as they travel through the pipeline. They remove wax, paraffin and water from the pipeline. Smart pigs contain instruments which measure and record various aspects of pipeline integrity.
Should a pipeline need repair, valves in the pipeline are used to isolate the section and the damaged area is either repaired or replaced. Valves are located at regular intervals along the pipeline so that only small sections and not the entire line need to be purged.
Pipeline Inspection Tools
Although ‘pigs’ have been used since early in the history of pipelines to keep internal walls clear of wax and other foreign material; ‘smart pigs’ with recording instruments were introduced in the 1960s. Smart pigs use ultrasonic waves or magnetic resonance to detect and record pits, fatigue cracks and other thickness variations in the pipeline walls before problems occur. Ongoing advances in smart pig technology provide for detection on a smaller and smaller scale. Most smart pigs now have GPS capabilities, improving the ability to locate such potential problems.
Use of Draft Reducing Agents – When fluids flow through a pipeline, friction with the pipe causes turbulent flow near the pipe wall. Draft reducing agents (DRAs) composed of long-chain polymers were developed in the 1940s to reduce this turbulence. They are injected into the fluid stream at pump stations. Continuous research and development has increased the efficiency of DRAs such that the amounts used are on the order of 10 to 20 parts per million. Leak DetectionMost pipeline systems are monitored remotely from computerized control centres. Control valves located at regular intervals along the line close automatically if pressure drops are detected to limit the amount of throughput spilled. Pipelines are also monitored by low-flying aircraft and ground crews with specialized detection equipment. In-line inspection equipment is also used to detect potential problems with the pipe and joints or welds. Pipeline operators can also “walk the line” and locate any leaks with highly sensitive detection equipment.