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Choice of Buffer Solution for Stainless Steel OCTG at Laboratory Corrosion Test to Carry Out SSC and SCC Resistance

This paper reviews a theoretical background of buffer solutions for stainless steel oil country tubular goods materials at laboratory corrosion test, and then the concept is applied to NACE-TM0177-based solution and modified solutions.

 

Product Number: 51317--9288-SG
ISBN: 9288 2017 CP
Author: Yasuhide Ishiguro
Publication Date: 2017
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Corrosion environment in real oil/gas well is very stable and can be regarded as equilibrium state. Therefore pH is very stable at each depth level of well from wellhead to bottomhole. The pH tends to stay the same in formation water and in condensed water as well. Buffer solution should be used to evaluate corrosion resistance for OCTG materials and the stability of buffer solution which corresponds to the capability to keep targeting pH throughout test duration is important to carry out laboratory corrosion testsThis paper reviews a theoretical background of buffer solution for stainless steel OCTG materials at laboratory corrosion test and then the concept is applied to NACE-TM0177-based three kinds of solution: (1)solution-A-based buffer solution (0.5%CH3COOH with CH3COONa) (2)solution-B-based buffer solution (2.5%CH3COOH + 0.41%CH3COONa with CH3COOH or CH3COONa) and (3)solution-C-based non-buffer solution (0.4g/L CH3COONa with HCl or NaOH). Through these comparative discussion it is made clear that the stability of each buffer depends on targeting pH in test condition. When compared between Solution-A-based “0.5%CH3COOH/ CH3COONa” solution and solution-C-based “0.4g/L CH3COONa/HCl” the buffer stability changes at around pH3.4-3.5. At over the pH the former has higher buffering stability than the latter but at below the pH the latter is much stable than the former.In addition to theoretical approach SSC test results are compared and reported when using different buffer solution. Also bicarbonate and high-pressurized CO2 buffer system will be also discussed.

Key words: buffer solution, acetic acid, acetate, bicarbonate, buffering stability, buffering capacity, sour environment, H2S-containing environment, NACE-TM0177, NACE-MR0165, ISO15156, EFC-17

Corrosion environment in real oil/gas well is very stable and can be regarded as equilibrium state. Therefore pH is very stable at each depth level of well from wellhead to bottomhole. The pH tends to stay the same in formation water and in condensed water as well. Buffer solution should be used to evaluate corrosion resistance for OCTG materials and the stability of buffer solution which corresponds to the capability to keep targeting pH throughout test duration is important to carry out laboratory corrosion testsThis paper reviews a theoretical background of buffer solution for stainless steel OCTG materials at laboratory corrosion test and then the concept is applied to NACE-TM0177-based three kinds of solution: (1)solution-A-based buffer solution (0.5%CH3COOH with CH3COONa) (2)solution-B-based buffer solution (2.5%CH3COOH + 0.41%CH3COONa with CH3COOH or CH3COONa) and (3)solution-C-based non-buffer solution (0.4g/L CH3COONa with HCl or NaOH). Through these comparative discussion it is made clear that the stability of each buffer depends on targeting pH in test condition. When compared between Solution-A-based “0.5%CH3COOH/ CH3COONa” solution and solution-C-based “0.4g/L CH3COONa/HCl” the buffer stability changes at around pH3.4-3.5. At over the pH the former has higher buffering stability than the latter but at below the pH the latter is much stable than the former.In addition to theoretical approach SSC test results are compared and reported when using different buffer solution. Also bicarbonate and high-pressurized CO2 buffer system will be also discussed.

Key words: buffer solution, acetic acid, acetate, bicarbonate, buffering stability, buffering capacity, sour environment, H2S-containing environment, NACE-TM0177, NACE-MR0165, ISO15156, EFC-17

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