Abstract
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.
Highlights
Highest strength combined with excellent corrosion resistance are key requirements for most applications in the oil and gas industry
The aim of this work is to characterise the resistance to hydrogen induced stress corrosion cracking (HISCC) and chloride-induced stress corrosion cracking (Cl- stress corrosion cracking (SCC)) of a new high-strength, highly corrosion resistant CrNiMnMoN stainless steel and to point out the importance of material testing in the cathodic and anodic potential range
Cathodic hydrogen charging in neutral solutions with the addition of thiourea leads to hydrogen values up to 25 wt.-ppm, which does not lead to failure when testing with constant load at 1.2 times the yield strength
Summary
Highest strength combined with excellent corrosion resistance are key requirements for most applications in the oil and gas industry. There is an increased susceptibility to hydrogen induced stress corrosion cracking (HISCC) and chloride-induced stress corrosion cracking (Cl- SCC). With increasing strength [1] For this reason, established alloying concepts today are mostly limited to. CrMnN stainless steels alloys usually achieve excellent mechanical properties through solubility hardening, but are known to be susceptible to hydrogen embrittlement (HE) and stress corrosion cracking (SCC) [2]. CrNiMo stainless steels show excellent resistance to hydrogen embrittlement and to stress corrosion cracking, but they often do not have adequate mechanical properties. Some unstable austenitic stainless steels show strain-induced martensite formation at increased plastic deformation, which again leads to increased susceptibility to hydrogen embrittlement [3]. This paper deals with the resistance of a new hybrid CrNiMnMoN stainless steel
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