Corrosion Behavior of API 5L X70 Carbon Steels in Hydrogen Sulfide Environments

Macedo, Jonas Fernando; Fioravante, Igor Alexandre; Nakazato, Roberto Zenhei; Acciari, Heloisa Andréa; Codaro, Eduardo Norberto

doi:10.22068/ijmse.18.1.12

Volume 18, Issue 1 (March 2021) IJMSE 2021, 18(1): 118-127 | Back to browse issues page

‎ 10.22068/ijmse.18.1.12

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Macedo J F, Fioravante I A, Nakazato R Z, Acciari H A, Codaro E N. Corrosion Behavior of API 5L X70 Carbon Steels in Hydrogen Sulfide Environments. IJMSE 2021; 18 (1) :118-127
URL: http://ijmse.iust.ac.ir/article-1-1976-en.html

Corrosion Behavior of API 5L X70 Carbon Steels in Hydrogen Sulfide Environments

Jonas Fernando Macedo

, Igor Alexandre Fioravante

, Roberto Zenhei Nakazato

, Heloisa Andréa Acciari

, Eduardo Norberto Codaro

Abstract: (11644 Views)

As we all know, corrosion of pipelines by hydrogen sulfide is the most worrying factor in the production and transport of oil and gas. In this work the corrosion behavior of API 5L X70MS and X70MO low carbon steels in hydrogen sulfide environments was investigated. Hydrogen induced cracking and sulfide stress cracking tests were carried out according to NACE TM0177 standard. After testing, blisters and cracks were observed only in X70MO steel, probably due to its lower grain refinement and banded microstructure. Internal cracks seem to be initiated in elongated MnS inclusions. Corrosion process was studied by obtaining potentiodynamic polarization curves, which were registered after open circuit potential measurements, at room temperature. Both steels showed general corrosion in NACE 177A solutions, but the corrosion rate values in H₂S-saturated solution were about an order of magnitude higher than those ones in deaerated solution. Hydrogen permeation w::as char::acterized in accordance with ASTM G148 standard. In deaerated H₂SO₄ solution, permeation measurements were similar for both steels. In H₂S-saturated solution, X70 MO exhibited higher hydrogen oxidation current values than X70 MS. H₂S seems to promote the reduction of protons and increase the concentration of hydrogen atoms in the solution/steel interface, favoring the diffusion process. As X70MO has a coarse microstructure, it offers more pathways for hydrogen diffusion.

Keywords: X70 steel, Hydrogen induced cracking, Sulfide stress cracking, Sour corrosion, Low carbon steel.