Sour Corrosion of C110 Steel and Its Influence by Galvanic Couple and Stress

Abstract

Combinational metals of casing or tubing string have been extensively used in deep sour gas wells because of their corrosion resistance and low costs. C110 carbon steel and G3 alloy connected by a thread joint under different stresses represent a typical application of dissimilar metals in such a case. Around the contact part, complex corrosion can occur, including general, galvanic, and stress corrosion. To evaluate such corrosion, simulation experiments were conducted. Three specimens involving (1) a single piece of C110, (2) a galvanic couple of G3 alloy and C110, and (3) an elastic-and plastic-stressed C110 were separately placed in a high-pressure and high-temperature (HPHT) autoclave containing brine water and dissolved H 2 S, CO 2 , and elemental sulfur. After corrosion at 120 °C and 65 MPa for seven days, the specimens were examined by various methods, including weight loss, potential dynamic polarization, electrochemical impendence spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectrometry (XPS). The experimental results showed that sour corrosion of C110 in the vapor is similar to that in solution. The galvanic effect on C110 corrosion by G3 was not evident based on the measurement of the limited increment of corrosion rate. Slower acceleration for corrosion was also observed for C110 when elastic stress was applied. However, plastic deformation significantly stimulated the corrosion rate of C110. The yield strain was found to change the polarization behavior of the anode and the performance of the corrosion scale. The corrosion mechanism is discussed in detail based on an analysis of the surface morphology, composition, and electrochemical performance of the scale, together with theories of the supercritical state, semiconductors, and mechano-electrochemistry.

Mechano-electrochemical modelling of corroded steel structures

“…Under external load, it has been generally agreed that the plastic strain will significantly reduce the corrosion resistance by directly enhancing the anodic reaction [7,11,14,16,[21][22][23][24][25][26] while the hydrogen evolution was reported to increase as well [21,22]. Despic et al [11] observed that a negative corrosion potential shifted by up to 30 times, with a marked increase in the anodic current density at the onset of the tensile plastic strain and reached an asymptotic value gradually.…”

A Critical Review on Corrosion and its Prevention in the Oilfield Equipment

“…Ren et al [38] evaluated the use of single piece of C110 carbon steel of casing or tubing and different stresses in deep sour gas wellsunder high-pressure (65 MPa) and high-temperature (120°C) autoclave containing brine water for seven days and dissolved H 2 S, CO 2 and elemental sulfur.The results showed that complex corrosion can occur around the contact partincluding general, galvanic, and stress corrosion and the sour corrosion of C110 steel in the vapor is similar to that in solution.…”

Corrosion Resistance of 13Cr Steels

“…This development leads to the exploitation of materials in extreme conditions [8][9][10][11][12], resulting in premature equipment failure [13][14][15][16][17][18] when operating in aggressive environments containing chlorine ions (Cl − ), carbon dioxide (CO 2 ), and hydrogen sulfide (H 2 S). Sulfide stress corrosion cracking (SSC), which is typical for materials in a hydrogen sulfide-containing environment, causes metal cracking under the action of corrosion and tensile stresses in the presence of moisture and hydrogen sulfide [9,[18][19][20][21].…”