engleski

Evaluation of Mn-V Steel Tendency to Hydrogen Embrittlement

Recently great attention is given to investigations related to oil and natural gas exploation, especially from the respect of material selection used for production of tubular equipment. In these conditions tubes destructions caused by mechanical damages are less frequent than destructions caused by various corrosion crack forms and especially corrosion cracks in sulphide conditions, with H2S as a dominant component. Results of mechanical properties and evaluation to tendenca of seamless tubes in as rolled and heat treated condition, produced from media carbon Mn-V steel to hydrogen embrittlement by method of cathode polarization at the constant current density of 4.0 mA/cm2 are presented in this paper besides the above stated possible tube destruction forms in the conditions of oil and natural gas exploation. The fractographic analysis of fractured samples surfaces after cathode polarization was also performed by scanning electron microscope. It was found that tubes in the as-rolled condition (no heat treatment) show great tendency to hydrogen embrittlement with the values of the calculated embrittlement indeks of 86.4%. By normalization (900oC/30 min., air) of tubes, the resistance to hydrogen embrittlement was not improved compared with the as-rolled condition. The heat treatment (quenching+tempering) resulted in a great resistance of tubes to hydrogen embrittlement with the calculated indeks of 25.1%. The stated results are proved by the fractographic analysis of morphology of fracture that are explicity brittle for tubes without heat treatment, but trough for quenched and temepered tubes. Therefore it can be calculated that from the aspect of mechanical properties and corrosion resistance the most suitable tubes for use in the oil and gas wells are those quenched and tempered at high temperatures (700oC).

Mn-V steel, hydrogen embrittlement, heat treatment, cathodic polarization

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