This paper is about a study on the impact(s) of elemental and ionic mercury (Hg) to carbon steel corrosion in sweet and sour environments with and without Corrosion Inhibitor(CI) injection.
Evaluation on the effect of Hg deposition and the corrosion behavior via Corrosion rate using Linear Polarization Resistance (LPR), solution properties, surface profile and corrosion product analysis are performed. Low pressure bubble test and autoclaves test are conducted under multiple variables to study the corrosion rate behavior. Fluid Analysis is performed using ICP-OES and XRD to analyse the chemical reaction of the fluid. Surface analysis is conducted using Visual inspection and XRF.
The bubble test analysis shows that elemental and ionic Hg does not affect the corrosion rates under CO2 environment. Likewise, in H2S-containing environment, elemental Hg do not effect H2S corrosion evidence by the low pre-corroding corrosion rate. However, ionic Hg is observed to influence H2S corrosion where higher corrosion rate is measured. This is potentially due to the reaction between ionic Hg and H2S lead to the formation of HgS, depriving carbon steel inhibitive effect by H2S. The addition of Corrosion Inhibitors is observed does not reduce the corrosion rate probably due to the reaction between the ionic Hg and the sulphide element from the CI resulted into decreasing of filming tendency. HPRCE Autoclave result shows that CI had successfully reduce the corrosion rate to the targeted corrosion rate provided higher CI injection dosing is introduced.Significant HgS spectrum observed during XRD analysis reflecting ionic Hg mighthave reacted with H2S and CI. This supported that the presence of ionic Hg might have interfered the inhibitive mechanism of the CI and delayed the formation of passive layer on the metal. ICP-OES and XRF indicated Hg traces potentially due to high reaction rate between ionic Hg and injected CI thus accelerated the formation of HgS.
CI formulation without any sulphide composition should be used if ionic Hg is present in order to ensure the CI effectiveness and it consumption during operation. In the event where the CI formulation cannot be changed, an enhanced pre-qualification evaluation as conducted in this study is to be carried out if ionic Hg is detected in the system to ensure the CI is effective and compatible to be injected.