Evaluation of EDTA and GLDA Corrosion on S13Cr-110 Metal Alloy at High Temperature and High Pressure With and Without Salt

As the petroleum industry has moved to deeper formation at high temperatures (>200°F) in more corrosive environments, both stimulation fluids and well tubing metallurgies have changed. Traditional well stimulation fluids such as HCl have been replaced by chelating agents such as ethylene diamine tetra-acetic acid (EDTA). In offshore environments, where environmental regulations are stricter, biodegradable and environmentally friendly chelating agents such as glutamic acid N, N-diacetic acid (GLDA) are preferred over EDTA. Well tubing designs have progressed from low carbon steel alloys such as L-80 and P-110 to corrosion resistant alloys (CRA’s) such as S13Cr-110 to account for acidic and sour environments. There is a need to understand the corrosion of CRA alloys such as S13Cr-110 with chelating agents (EDTA and GLDA) as they interact with the metal during stimulation work (approximately 6 hr). In this work, the corrosion rate of 20 wt% EDTA and 20 wt% GLDA on S13Cr-110 is analyzed at high temperature (300°F and 350°F) and high pressure (>1000 psi) for 6 hr. In addition, the effect of a 5 wt% brine (NaCl) solution investigated. All pH values were held to 4 with the exception of EDTA in the presence of salt (pH = 9). This was due to the low solubility of EDTA in acidic solutions with high ionic strength. The results show that corrosion rate increases with temperature, GLDA is more corrosive than EDTA under the same conditions, and that EDTA at pH 9 is more corrosive than EDTA at pH 4. All corrosion rates calculated are