Corrosion rates of API 5L X-52 and X-65 steels in synthetic brines and brines with H₂S as a function of rate in a rotating cylinder electrode

This paper investigates the importance of the hydrodynamic conditions in the corrosion rates in steel type API 5L grade X-52 and X-65 in synthetic brine with and without H₂S at 30 and 60°C, tested in a rotating cylindrical electrode (RCE) under hydrodynamic flow conditions within a rotation range of 0 to 7500 rpm (4.319 m/s). It was found that the rotation rate influences the electrochemical process which takes place in the steel surface because it increases the corrosion rate with increasing rotational rate. As expected, it was observed that at a temperature of 60°C, corrosion rates higher than the temperature of 30°C were obtained, this effect being more evident in media with H₂S. And the effect of H₂S in the steel, was the one of increasing the corrosion rate drastically as a function of the rotational rate. In the absence of H₂S, the corrosion products formed on the steel surfaces were composed mainly of iron oxides, and in brine containing H₂S the corrosion products were composed mainly of iron oxides and some sulfur (mackinawite) which was nonadherent and cracks easily. The steel has the best behavior under absence of H₂S at 30°C is the API 5L X-52 as it has the lowest values of corrosion rates not so when the temperature is increased to 60°C where the steel has the best behavior is the API 5L X-65. Under presence of H₂S at 30 and 60°C the steel has the best performance with respect to the corrosion rate by exhibiting lower values is the API 5L X-52.