Type 304L stainless steel (304L) tray floors and shells in Diglycolamine (DGAR) regenerators often fail from general corrosion. The DGA units remove CO2 from natural gas using a 65 wt% aqueous solution of DGA. The raw gas contains 6 mol% CO2 and 2~3 ppm H2S.

In order to mitigate this corrosion problem through alloy selection, corrosion coupons of seventeen alloys were fixed on tray floors in a DGA regenerator to evaluate their corrosion resistance.

Based on these test results and price, Alloy 20Cb3 and Commercially Pure titanium (CP Ti) were selected to compare their corrosion and resistance mechanisms with those of 304L in the laboratory employing dynamic Jet Impingement testing.

The changes in corrosion rate were monitored by the polarization resistance technique, and the corrosion mechanisms were studied by the interpretation of electrochemical impedance data.

CP Ti had the best corrosion resistance in all the environments tested. In the most severe test condition, the original passive film of CP Ti was initially degraded. However, a new passive film rapidly formed and the corrosion resistance returned. Alloy 20Cb3 showed corrosion resistance marginally better than 304L.

Judging from the plant evaluation and the laboratory research study, CP Ti was the most suitable candidate material for the DGA regenerators.

Subject
Electrochemical impedance spectroscopy, Materials, Electrochemical cells, Corrosion rate, Wall shear stress, Gas pressure, Nyquist plots, Test environments, Sulfides, Corrosion resistance, Stainless steel, Titanium alloys, Linear polarization resistance
Keywords:
materials evaluation, dynamic conditions, CO2 removal, DGA, polarization resistance, electrochemical impedance
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2002
GOV
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