Many factors can cause pipeline failures, including overpressure, weld resistance, joint issues and construction damage. Yet, in the last 15 years, almost 60% of oil and gas production pipeline incidents in Canada have been caused by internal corrosion.
Corrosion is the deterioration of a substance, usually a metal, due to interaction with its environment. Oil and gas pipelines are vulnerable to corrosion in part because of the use of carbon and low-alloy steels.
Adding corrosion inhibitors, or chemical substances that decrease corrosion rates, is one of the most effective methods to control internal corrosion of pipelines. However, no single inhibitor suits all situations, which creates a challenge for industry when it comes to selecting the best product for the job.
To help oilfield and refinery industries select and use the best corrosion inhibitors, Natural Resources Canada’s CanmetMATERIALS, CanmetENERGY-Devon laboratories and industry partners have developed five standards for the testing and use of corrosion inhibitors.
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| A close up of the CANMET corrosion test flow loop at an operating oil wellhead |
“Before the standards, each laboratory used a different methodology, and each ranked the inhibitors differently,” says Dr. Sankara Papavinasam, Senior Research Scientist at CanmetMATERIALS in Hamilton. "The development of standards was imperative to help identify which methodologies are ideal and to ensure that the results are reproducible.”
Identifying the Best Methodology
The ideal methodology to identify the best corrosion inhibitor reproduces four elements of an operating pipeline: the composition of the fluid transported (oil, water and gas), the pipeline material (e.g., carbon steel), the in-wall pipeline pressure, and the temperature of the fluid and the flow conditions.
The flow conditions are the most important, as well as the most difficult to measure. They depend on the flow rates of gas, oil and water, temperature, and pressure. To simulate the flow, scientists use a parameter called wall shear stress. The shear stress is the measure of the force with which the fluid knocks on the wall of the pipeline and influences the corrosion rate.
After several experiments in the field and laboratory, CanmetMATERIALS and CanmetENERGY identified three top-ranked methodologies that simulate field operating conditions and provide consistent results: the rotating cage, the rotating cylinder electrode and jet impingement. Standards were then developed prescribing the use of each.
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| Diagram of Jet Impingement methodology |
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| The rotating cage,one of the three top-ranked methodologies |
“The rotating cage, for example, is simple, compact and simulates most pipeline operating conditions (typically between 20 and 200 Pascal (Pa)) of wall shear stress,” says Sankara. The rotating cylinder does not simulate extreme field operating conditions, but can effectively be used to evaluate inhibitors up to 20 Pa of wall shear stress. "When operating conditions are extreme, typically above 200 Pa, the jet impingement apparatus is effective,” he adds.
To develop the standards, CanmetMATERIALS and CanmetENERGY-Devon collaborated with an industry consortium that gave technical advice. Experiments were conducted in other labs to ensure that the methodologies, procedures and results are reproducible.
Standards Now Recognized by ASTM
The American Society for Testing and Materials (ASTM), a globally recognized body that develops international standards for improving safety standards, recently approved and published the last of the five new corrosion inhibitor standards proposed by CanmetMATERIALS.
“Now that industries can use standardized methodologies, corrosion inhibitor selection will be more reliable,” says Dr. Alebachew Demoz, Research Scientist at CanmetENERGY-Devon. “Selecting the best corrosion inhibitor will contribute to reducing oil and gas production pipeline leaks and increase their safety.”
Source: http://www.nrcan.gc.ca/science/story/1385
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