Sulfide inclusions are preferred nucleation sites for the localized corrosion of carbon and stainless steels. Thus, inclusions distribution and composition are important for the occurrence of pitting, crevice and the different forms of stress corrosion cracking. Amines are usually used for the removal of sulfides, with the precipitation of carbamates by the production of environmental friendly fuels with low S contents. On the other hand, amines are also used associated to formation/injection waters simultaneously to CO₂ reinjection by the offshore oil production at high pressures, usually under the assumption that it will act as a corrosion inhibitor, as well.

In the present work, we show that amines, usually seen as corrosion inhibitors may enhance the attack to sulfide inclusions in unalloyed carbon steels. For this, artificial galvanic elements with carbon steel (AISI 1006) and MnS tablets (Figure 1.a and 1.c), simulating an inclusion, were studied by SVET (scanning vibration electrode technique) (Figure 1.b and1.d) and other techniques to evaluate the influence of amine (1% tetraethylenepentamine-TEPA) on the corrosion in Na₂SO₄solutions. Carbon steels (e.g. SAE1006) exposed to dilute sulfate solutions show the typical passive behavior with pitting at higher potentials. The amine “TEPA” shifts the pitting potential to higher values, as expected (Fig. 3a). MnS inclusions show the opposite behavior and its dissolution is promoted when TEPA is added in significant concentrations (Fig. 3b). Accordingly, SVET measurements show that the addition of TEPA can invert the galvanic pair formed by Fe-MnS (Fig. 1). At OCP, a synthetic MnS inclusion is attacked progressively by TEPA as Fig.2 shows for different exposure times. This has significant consequences for the initiation of pitting and stress corrosion cracking of steels, as verified by SVET measurements under simultaneous mechanical strain.