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.

Microbiological methanation is investigated in an underground natural gas reservoir. Since H2 is involved in the process, hydrogen embrittlement of steel must inevitably be considered. Therefore, a routine for testing has been developed and a unique autoclave test bench was designed to simulate field conditions. The 2205 duplex stainless steel (UNS S31803) was investigated. Constant load tests (CLTs) and immersion tests with subsequent hydrogen analyses were performed. The specimens were exposed to different partial pressures of H2 under both dry and wet conditions (with brine). Additionally, the influence of CO2 under wet conditions was covered. Tests were performed at two different temperatures (25°C and 80°C) and lasted for 30 days. In general, the duplex stainless steel shows a good resistance to hydrogen embrittlement, but a significantly higher hydrogen uptake was obtained compared to other steel grades.

A new high-nitrogen austenitic stainless steel with excellent mechanical properties was tested for its resistance to stress corrosion cracking. The new conventional produced hybrid CrNiMnMoN stainless steel combines the excellent mechanical properties of CrMnN stainless steels with the good corrosion properties of CrNiMo stainless steels. Possible applications of such a high-strength material are wires in maritime environments. In principle, the material can come into direct contact with high chloride solutions as well as low pH containing media. The resistance against chloride-induced stress corrosion cracking was determined by slow strain rate tests and constant load tests in different chloride-containing solutions at elevated temperatures. Resistance to hydrogen-induced stress corrosion cracking was investigated by precharging and ongoing in-situ hydrogen charging in both slow strain rate test and constant load test. The hydrogen charging was carried out by cathodic charging in 3.5 wt.% NaCl solution with addition of 1 g/L thiourea as corrosion inhibitor and recombination inhibitor to ensure hydrogen absorption with negligible corrosive attack. Slow strain rate tests only lead to hydrogen induced stress corrosion cracking by in-situ charging, which leads to total hydrogen contents of more than 10 wt.-ppm and not by precharging alone. Excellent resistance to chloride-induced stress corrosion cracking in 43 wt.% CaCl2 at 120 °C and in 5 wt.% NaCl buffered pH 3.5 solution at 80 °C is obtained for the investigated austenitic stainless steel.

The resistance to chloride-induced stress corrosion cracking was investigated on a high-strength CrNiMnMoN austenitic stainless steel in the hot-rolled and in different cold-drawn states. The resistance against chloride-induced stress corrosion cracking was determined by slow strain rate tests in different chloride containing solutions at elevated temperatures. A fracture analysis was carried out using scanning electron microscopy. Improved resistance is obtained by the formation of deformation-induced twins. In addition, synchrotron X-ray diffraction measurements show full austenite stability during all cold-drawing steps. Graphical abstract

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