Abstract
The paper reports on a study of the susceptibility to sulphur stress corrosion connected with hydrogen embrittlement in 12 heats of an engineering steel of C 105 type used for the production of drill pipes. The investigated heats differed in sulphur contents and in microalloying with niobium, titanium and/or vanadium. Tests were performed in the presence of H₂S in a NACE solution (specification TM-02-84) with a pH-value of 3.5 under a load equal to 80% of the Re_min. The steel is required to withstand 720 hours of exposure in NACE solution. The findings prove that life forecasts must always take into account a whole set of microstructural factors, especially the size and distribution of sulphide inclusions, as well as the conditions that govern the uniform distribution of hydrogen atoms in the material. The experimental results were compared with the results of the prediction based on the modelling of hydrogen atom trapping on inclusions.

Key words
steel of C 105 type, corrosion, sulphur contents, microalloying with niobium, titanium and/or vanadium

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