Standards specify oilfield corrosion protection

Edited by the Engineeringtalk editorial team Mar 22, 2006

New standards on thermal spraying fills a void in zinc and tin alloy industry.

ASTM International Committee G01 on Corrosion of Metals has an ongoing commitment to help the oilfield and refinery industries adopt and use state-of-the-art techniques to select corrosion inhibitors.

As part of this commitment, two new standards developed by Subcommittee G01.05 on Laboratory Corrosion Tests have recently been published: G184, "Practice for evaluating and qualifying oilfield and refinery corrosion inhibitors using the rotating cage", and G185, "Practice for evaluating and qualifying oilfield and refinery corrosion inhibitors using the rotating cylinder electrode".

These standards are the result of almost three years of close collaboration between Task Group G01.05.11 and oil companies, inhibitor suppliers, researchers, consultants, and educators.

The two standards support the optimised selection of inhibitors by end users and the development and formulation of more efficient inhibitors by suppliers.

Oil and gas pipelines are vulnerable to corrosion.

Corrosion results, in part, from the use of carbon and low-alloy steels in pipeline construction.

Although these materials are cost-effective, they characteristically exhibit poor corrosion resistance.

To control corrosion, the industry uses corrosion inhibitors, primarily in upstream pipelines carrying oil and gas from the wells to the processing plants.

The annual inhibitor market in North America alone is approximately 1.6 billion dollars.

No single inhibitor, however, suits all situations.

The efficiency of an inhibitor depends not only on the volumes and properties of the produced fluids and on the properties of the inhibitor itself, but also on the way it is applied and the operating conditions of the system, such as temperature, flow rate, and pressure.

"Inhibitors should be screened using quantitative methods (rotating cylinder electrode, rotating cage, or jet impingement)".

"Among the quantitative methods, the rotating cylinder electrode is used only up to a wall shear stress (a parameter to correlate the flow effect in different geometries) of 20Pa, whereas the rotating cage can be used up to 200Pa", explained Dr Sankara Papavinasam, Canmet Materials Technology Laboratory, Natural Resources Canada, Ottawa, Ontario, Canada.

"Publication of standard practices G184 and G185 provides the oilfield and refinery industries with a common procedure to conduct experiments for evaluating corrosion inhibitors", he added.

ASTM standard G170, "Guide for evaluating and qualifying oilfield and refinery corrosion inhibitors in the laboratory", published in 2001, describes procedures to evaluate corrosion inhibitors (including inhibitor efficiency and secondary corrosion inhibitor properties), whereas G184 and G185 prescribe procedures to perform rotating cage and rotating cylinder electrode experiments, respectively.

"In the absence of the standards, agreement between the inhibitor supplier, the inhibitor user, and any third-party evaluation laboratory on the merits of specific corrosion inhibitors has often been quite difficult to achieve", explained Dr Milan Bartos, Nalco Company, Sugar Land, Texas.

"In extreme cases, each laboratory would identify a different inhibitor as the number-one choice".

"The three laboratories could not agree on which inhibitor would be the best, because each laboratory used a different methodology, or a different procedure".

"Utilising standard methodologies, such as Practices G184 and G185, to evaluate corrosion inhibitors will be extremely useful in achieving consistency of results among different laboratories".