Effect of H2S/CO2 Corrosion Scale On Hydrogen Permeation

Hao, Wenhui (Corrosion and Protection Center, Key Laboratory for Environmental Fracture (MOE), University of Science and Technology Beijing) | Zhang, Lei (Corrosion and Protection Center, Key Laboratory for Environmental Fracture (MOE), University of Science and Technology Beijing) | Yang, Jianwei (Shougang Research Institute of Technology) | Li, Han (Corrosion and Protection Center) | Ding, Jinhui (Corrosion and Protection Center, Key Laboratory for Environmental Fracture (MOE), University of Science and Technology Beijing) | Lu, Minxu (Corrosion and Protection Center, Key Laboratory for Environmental Fracture (MOE), University of Science and Technology Beijing)

OnePetro 

ABSTRACT:

In this paper, electrochemical hydrogen permeation method is employed to investigate the effects of H2S/CO2 corrosion scales on the hydrogen permeation of pipeline steel. In order to reveal the mechanisms of this kind of phenomena under high H2S partial pressure, high temperature and pressure corrosion simulation experiments and Devanathan-Stachurski cell tests are used to analyze the effects of different corrosion product scales on hydrogen permeation under various H2S containing environment condition. The results show that, the scale dominated by Mackinawite promoted the hydrogen permeation behavior, otherwise the scale dominated by Pyrrhotite reduced the steady state flux of hydrogen.



INTRODUTION

Pipeline steel has been widely utilized in oil and gas transfer due to its high strength and ductility. However, in the transportation of oil and gas, H2S, CO2 and other acids make the failures of pipeline steels related to hydrogen become increasingly outstanding.1,2,3 Failures will not only result in leakage, but cause significant economic losses and casualties.4 When H2S and CO2 coexist, electrochemical corrosion and cracking damage must be taken into consideration simultaneously. Hydrogen induced cracking (HIC) of pipeline steel caused by H2S in sour gas field is one of the most important failure forms. Although NACE TM0284 can be used to assess HIC, there is a lack of sufficient knowledge of HIC risk under especially sour conditions such as H2S partial pressure higher than 1MPa. For HIC, the action after hydrogen atoms into metals, the crack propagation and degradation of material properties have got more attention.5, 6 However, most of the researches on HIC were usually separated from the electrochemical corrosion of H2S/CO2, and the effects of corrosion scales on the combination of hydrogen atoms and the process of hydrogen into metals might be ignored. At this condition, since the electrochemical corrosion under H2S/CO2 coexistence conditions is very serious, the formation of corrosion product scale on the steel surface might significantly effect on the hydrogen permeation and the occurrence of HIC. In this paper, electrochemical hydrogen permeation method is employed to investigate the effects of H2S/CO2 corrosion scales on the hydrogen permeation of pipeline steel.



EXPERIMENT PROCEDURE

The chemical composition of the steel is shown in Table 1. The steel specimens in form of membrane were prepared having 0.5 mm thickness and 45 mm of diameter. The microstructure consists of ferrite and pearlite. Both sides of the membrane were ground with carborundum paper down to 1000 grit and polished. After pickling with 3 mol/L HCl, and degreasing with acetone, one side (detection side) of the steel membrane was deposited with a film of nickel in Watt's bath of 250 g/L NiSO4·7 H2O + 45 g/L NiCl2·6 H2O +40 g /L H3BO3 using cathodic current density of 10 mA/cm2.7 In order to obtain the corrosion scale with different composition covered on the other side (input side) of membrane, a high temperature and high pressure autoclave was employed to simulate sour corrosion situations under different experiment conditions (denoted by 1, 2, and 3), as shown in Table 2.