Abstract
Armco iron and L80 steel (according to API 5CT) were charged under various conditions due to often not knowing the exact amount of hydrogen absorbed during operation and laboratory charging. These two materials were charged in sodium chloride (NaCl), sulfuric acid (H2SO4), both with and without addition of thiourea (CH4N2S), and in H2S (NACE TM0177) at open circuit potential.Additionally, cathodic charging was done in sodium chloride and sulfuric acid, both with thiourea added at a current density of 1 mA/cm2. The charging time was between 2 and 336 h for both methods. Prior to the charging, the specimens were cleaned in acetone and the bulk hydrogen content of the two materials was determined. After charging, the specimens were ground with a silicone carbide paper and the hydrogen content was measured with a thermal conductivity cell after hot extraction at 950 °C.Most of the immersion tests at open circuit potential resulted in hydrogen concentrations of up to 1 wt. ppm, while the cathodic charging led to values of up to 4 wt. ppm. In addition, the NACE TM0177 test provided the highest hydrogen concentrations and was the only test to show higher hydrogen concentrations for Armco iron than for L80 steel.
Highlights
As early as 1874, Johnson first found a connection between the embrittlement of steel and the absorption of hydrogen after immersion in acids [1]
In order to overcome the required enthalpy of dissociation, it is necessary to carry out pressurized hydrogen charging tests at increased hydrogen partial pressure and/or increased temperatures
Before the test was carried out, the hydrogen content of both test materials was determined in the as-delivered condition
Summary
As early as 1874, Johnson first found a connection between the embrittlement of steel and the absorption of hydrogen after immersion in acids [1]. Researchers have been trying to explain the mechanism of hydrogen embrittlement, while the absorption of hydrogen is often overlooked. The aim of this contribution is to explain the mechanisms of hydrogen uptake and to determine the hydrogen uptake of Armco iron and L80 steel under various conditions. In order to overcome the required enthalpy of dissociation, it is necessary to carry out pressurized hydrogen charging tests at increased hydrogen partial pressure and/or increased temperatures. Physical adsorption, hydrogen is adsorbed in molecular form via Vander-Waals forces on the surface. In the second sub-step, chemical adsorption, the hydrogen molecule dissociates in order to assume the energetically more favorable state at sliding stages or surface defects. The atomically present hydrogen can be absorbed by the material
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