Development of Green Corrosion Inhibitors for Preventing Under Deposit and Weld Corrosion
- A.E. Jenkins (Baker Petrolite) | W.Y. Mok (Baker Petrolite) | C.G. Gamble (Baker Petrolite) | G.E. Dicken (CAPCIS)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium on Oilfield Corrosion, 28 May, Aberdeen, United Kingdom
- Publication Date
- Document Type
- Conference Paper
- 2004. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 4.3.4 Scale, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 4.2 Pipelines, Flowlines and Risers
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Under-deposit/scale, pitting and weld corrosion are a major cause of localised corrosion failure in oil and gas production systems. Since advancement in instrumentation and the successful development of the localised corrosion test protocol in 2002, the technique has been widely used to study the inhibition of localised corrosion. The latest examples of its application are presented. Green corrosion inhibitors have been screened and their ability to inhibit under scale pitting has been determined. The work has allowed the key monitoring parameters in the inhibition of localised corrosion to be identified, which has resulted in a refinement of the test protocol. Additionally, the ability of corrosion inhibitors in preventing weld corrosion was also assessed. The ability of the corrosion inhibitors to be effective against weld corrosion and under deposit corrosion was demonstrated. The results established that specialised laboratory tests should be used to qualify inhibitors prior to field deployment.
Corrosion inhibitors are widely used within the oil and gas industry to prevent corrosion within pipelines due to the presence of CO2 and H2S. Laboratory corrosion inhibitor selection traditionally uses electrochemical techniques that determine inhibitor effectiveness in preventing general corrosion. Such tests include kettle tests, rotating cylinder electrode (RCE) and jet impingement1,2,3. However, within oil field pipelines and downhole tubing, carbon steel can be susceptible to several types of corrosion. These include pitting, under deposit and corrosion of weldments.
Field experience suggested that not all inhibitors are effective in inhibiting these forms of corrosion. In fact it is possible that some inhibitors, if injected at insufficient quantity, can accelerate the pitting rate and weld corrosion. Care must be taken when changing out inhibitors or starting inhibitor injection for the first time that the inhibitor will prevent or reduce the type corrosion that is present.
For fields where general corrosion is not the predominant type of corrosion present it is advisable that other tests be performed to investigate inhibitor performance against the form of corrosion present. For example, it is possible to assess inhibitor performance against pitting corrosion in sour environments by using weight loss coupons and visually inspecting coupons with a microscope for the presence of pits4,5. It is also possible with this technique to measure the maximum pit depth present in treated and untreated coupons. With this information it is possible to qualify inhibitor performance.
Additionally, an ambient pressure technique has been developed where an artificial pit electrode has been used to evaluate corrosion inhibitor performance in preventing localised corrosion6. Tests were able to distinguish between inhibitors which gave similar levels of protection against general corrosion.
The use of corrosion inhibitors can also enhance weld corrosion. Rothwell7 has reported based on field data, that corrosion inhibitors can have a detrimental affect on weld corrosion at low dose levels. Furthermore, a considerably higher dose level of inhibitor was required to inhibit weld corrosion compared to inhibiting the general corrosion rate.
Corrosion of weldments and under deposit pitting corrosion beneath barium sulphate scale deposits were recognised to be an important aspect of corrosion risk in an oil and gas production facility in the North Sea. Due to the awareness of minimising environmental impact, a laboratory test programme was initiated to identify more environmental friendly candidate corrosion inhibitors as potential replacements for the incumbent inhibitor. This paper gives details of how the artificial pit technique, weldment corrosion test and traditional test methods have been used in selecting a ‘green' corrosion inhibitor that is effective against under deposit and weldment corrosion.
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