| Abstract: | We applied the methods of fatigue failure in pure bending and of impact toughness to investigate the tube steels 17GS, 19G, 14GN, 14KhGS, 10G2S, and Kh52 (Czechoslovakia) of oil pipelines after different service times, and we also determined the stress intensity factors and strain aging co-effecients. The article shows that with loinger service time the tube steels become embrittled: the number of load cycles to failure decreases, impact toughness drops abruptly, and the strain-aging coefficient increases. In embrittled steels fatigue cracks become more ramified than in nonaged steels. It was established that in proportion to the length of operation of oil pipelines the residual life of the tube steels decreases in consequence of the embrittlement of structurally inhomogeneous regions of the metal. It is shown that specimens with welding seams fail 2–2.5 times more rapidly; this testifies to the intense aging in structurally inhomogeneous regions.All-Union Research Institute for the Construction and Planning of Oil Pipelines (VNIISPTnefti), Ufa. Translated from Problemy Prochnosti, No. 11, pp. 125–128, November, 1989. |
