The effect of H2S concentration on the corrosion behavior of carbon steel at 90 °C

Corrosion behaviour of carbon steel in different concentrations of HCl solutions containing H2S at 90 °C

The work reviews existing corrosion field testing and laboratory experiments in geothermal environment. The search covers all published research on the corrosion behaviour of carbon steel and corrosion resistant alloys (CRA) subjected to corrosive geothermal fluids at high temperature conditions. The objective is to gain better understanding of corrosion damage to commercial carbon steels normally used as a construction material for geothermal wells and surface facility. Corrosion-resistant alloys are likewise evaluated for performance as they are more and more being considered as alternative construction material. The different corrosion evaluation methods are also given with the advantages and their disadvantages discussed. The factors controlling the corrosion rate of geothermal fluids are salinity, pH, temperature, fluid flow velocity, dissolved gases and the formation of a stable protective passive film. The review shows that; while laboratory experiments mostly mirrors the field testing results. Laboratory testing generally fails to duplicate the mineral scale and corrosion products that provide the protective film. Field testing is recommended for material selection in new geothermal fluid environment.

Corrosion in geothermal environment Part 2: Metals and alloys

The effect of the surface roughness of carbon steel on corrosion properties was investigated using electrochemical tests, and surface and Kelvin probe force microscopy (KPFM) analyses. The results of electrochemical tests show that the corrosion rate of carbon steel is increased as the surface roughness increases. It was estimated using KPFM measurement that the difference in the Volta potential between the peak and the valley increased with increasing surface roughness. As the peak has a lower potential than that of the valley, the peak acts as an anode. The surface roughness affects the Volta potential, and the Volta potential difference is inversely proportional to electron work function (EWF). The larger difference in Volta potential between the peak and valley on the rougher surface and the smaller EWF accelerated the micro-galvanic corrosion between them. The surface analyses reveal that corrosion initiated along the peak lines. The results from this study suggest that an increase of surface roughness leads to a decrease of the corrosion resistance.

Influence of surface roughness on the electrochemical behavior of carbon steel

A potentiostatic double-step method for measuring hydrogen atom diffusion and trapping in metal electrodes—II. Experimental

The corrosion rates of low-carbon steel, and 304, 316 and 410/420 stainless steels in simulated geothermal media containing hydrogen sulfide have been measured by means of the polarization resistance technique. Good agreement was found between weight-loss and polarization resistance measurements of the corrosion rate for all the metals tested. Carbon steel formed a non-adherent film of mackinawite (Fe1 + xS). The lack of protection afforded to the steel by the film resulted in an approximately constant corrosion rate. The stainless steels also exhibited corrosion rates that were independent of time. However, the 410 and 420 alloys formed an adherent film consisting mainly of troilite ( FeS ) which provided only limited passivity. In contrast, the 304 and 316 alloys appeared to be essentially protected by a passive film which did not seem to involve an iron sulfide phase. However, all the stainless steels, particularly the 410 and 420 alloys, showed pitting, which indicated that some breakdown of the passive films occurred.

M. P. Glucina

Papers

The Corrosion of Carbon Steel and Stainless Steel in Simulated Geothermal Media

Corrosion of Carbon Steel and Stainless Steel in Simulated Geothermal Media.