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1 Zeszyty Naukowe. Mechanika / Politechnika Opolska

1 2007

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Hydrogen diffusion in micro alloy steels

Sojka J., Jonšta P., Rytířová L., Jerome M., Zajac J., Sozanska M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2007

Vol. 321, z. 89

121-122

Petroleum and natural gas systems can be contaminated with wet H2S. This environment is very aggressive to the steels used in the transport and processing of these products and it can result in various forms of hydrogen embrittlement. The reaction between wet H2S and the steel generates atomic hydrogen, which can be, at least partially, absorbed into the steel. In the absence of applied stress, the diffused hydrogen can cause hydrogen induced cracking (HIC). The resistance of steels to HIC is closely related to the microstructure features: nonmetallic inclusions, hard phase constituents, banded structures etc. In the presence of applied or residual stress, the failure process can occur by sulphide stress cracking (SSC) or stress oriented hydrogen induced cracking (SOHIC). In the case of SSC, steel resistance is commonly derived from its strength level. It is generally accepted that steels having tensile strength less than 690 MPa approx. are resistant to SSC. The role of microstructure is not emphasized although there are some works showing that microstructure can also play an important role in the case of SSC. In the previous works, it was proved that even in case of SSC the resistance of the steels can be improved by the heat treatment – quenching and tempering, if the banded structure of ferrite and pearlite is replaced by the tempered martensite and/or bainite. The resistance of the steel to the hydrogen embrittlement is affected by both the microstructure and hydrogen concentration. To understand the hydrogen embrittlement it is necessary to characterize also the hydrogen transport – diffusion. In this work hydrogen diffusion coefficient in micro alloy X52 and X60 API steels (tubes), having different microstructures - banded ferrite and pearlite after hot rolling and the mixture of tempered bainite and martensite after quenching and tempering, are evaluated. The role of specimen orientation is also taken into account.