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The ductile fracture arrest capability of gas pipelines is seen as one of the most important factors in the future acceptance of new high strength pipeline steels for high pressure applications. New North-European pipeline project is based on application of X70 pipes designed for high gas pressure of 9,8MPa. To study fracture propagation behavior in cold climate the full scale tests were carried out using longitudinally and spiral welded pipes with different microstructure of base metal. Results of the tests with crack propagation studies in predominately ferrite-pearlite (FP) and acicular ferrite (AF) steels possessing similar Charpy energy are presented. Crack propagation mechanisms in base metal and along spiral weld were studied and are presented with strain distribution along crack.

With the running fracture of the main gas pipeline, a longitudinal crack can stop propagating in one of two ways. The first way is arresting the crack without changing its direction due to the energy transferred from the expansion of the gas becomes less than the energy required to continue opening the crack. The second way is more common, when the crack changes the direction of its propagation from longitudinal to circumferential and forms a loopback. The known mathematical models describe and can predict only the first way to arrest the crack propagation, but so far they cannot simulate the second way. This paper shows that the reason for the realization of the second way is a change in the configuration ("flattening") of the cross-section of the pipe when a crack approaches. This leads to the appearance of radial normal stresses in the pipe wall. If the radial normal stresses exceed longitudinal ones, the planes of maximum tangential stresses change their positions from longitudinal to placing at an angle of 45° to the axis of the pipe. Since the metal is ductile, and the fracture results from tangential stresses, the crack changes its direction and is looped back. This situation takes place when the radius of curvature of flattening becomes less than the pipe diameter.

Äëÿ îïðåäåëåíèÿ ñîïðîòèâëÿåìîñòè òðóáíûõ ñòàëåé ðàçëè÷íîãî ðîäà ðàçðóøåíèÿì ðàçðàáîòàíà êîìïüþòåðíàÿ ìîäåëü ðàñïðîñòðàíåíèÿ ïðîòÿaeåííîé òðåùèíû â ãàçîïðîâîäå íà îñíîâå ìîäèôèöèðîâàííîé ëîêàëüíîé ìîäåëè Ãóðñîíà − Òâåðãààðäà − Íèäåëüìàíà. Ìîäåëü ïîçâîëÿåò îïèñûâàòü ïðÿìûå è êîñûå ñðåçû, à òàêaeå èõ êîìáèíàöèþ ïðè âÿçêîì ðàçðóøåíèè ìàëîìåðíûõ îáúåêòîâ (ñòåðaeíåé, ïëàñòèí, îáîëî÷åê). Ïðèâåäåíû äåòàëè ðåàëèçàöèè óêàçàííîé ìîäåëè â ïàðàëëåëüíîé êîíå÷íî-ýëåìåíòíîé êîìïüþòåðíîé ïðîãðàììå ÄÀÍÊÎ, ðàçðàáîòàííîé â ÐÔßÖ−ÂÍÈÈÝÔ. Îïðåäåëåíû ïàðàìåòðû ìîäåëè íà îñíîâå ëàáîðàòîðíûõ ýêñïåðèìåíòîâ ñ îáðàçöàìè èç òðóáíîé ñòàëè êëàññà ïðî÷íîñòè Ê65. Íà ÷èñëåííûõ ïðèìåðàõ ïîêàçàíà ðàáîòîñïîñîáíîñòü ìîäåëè. Ðåçóëüòàòû èñïîëüçóþòñÿ äëÿ ÷èñëåííîãî èññëåäîâàíèÿ äåôîðìèðîâàíèÿ, ðàçðóøåíèÿ îáðàçöîâ ïðè èñïûòàíèÿõ, äèíàìè÷åñêîãî ðàñïðîñòðàíåíèÿ òðåùèíû â òðóáîïðîâîäå. Êëþ÷åâûå ñëîâà: ñòàëè ìàãèñòðàëüíûõ ãàçîïðîâîäîâ, ìàëîìåðíûå îáúåêòû, âÿçêîå ðàçðóøåíèå, êîñûå ñðåçû, êîìïüþòåðíîå ìîäåëèðîâàíèå, ìåòîä êîíå÷íûõ ýëåìåíòîâ, ìîäèôèöèðîâàííàÿ ëîêàëüíàÿ ìîäåëü Ãóðñîíà − Òâåðãààðäà − Íèäåëüìàíà.

Ðàññìàòðèâàþòñÿ âîçìîaeíîñòè ïðèìåíåíèÿ ìîäèôèöèðîâàííîé ìîäåëè Ãóðñîíà − Òâåðãààðäà − Íèäåëüìàíà, êîòîðàÿ â ðàìêàõ ÷èñëåííîãî ìîäåëèðîâàíèÿ ïîçâîëÿåò ïîëó÷àòü ðåàëèçóåìûå â ýêñïåðèìåíòàõ íà îáðàçöàõ ïîâåðõíîñòè ðàçðóøåíèÿ, âêëþ÷àþùèå êîñûå ïîâåðõíîñòè. Âûïîëíåíî êîìïüþòåðíîå ìîäåëèðîâàíèå èñïûòàíèé ïî ñòàòè÷åñêîìó ðàñòÿaeåíèþ ïëàñòèí (ïðèç-ìàòè÷åñêèõ îáðàçöîâ) ñ êðàåâûì íàäðåçîì øåâðîííîãî òèïà − èíèöèàòîðîì íà÷àëà îáðàçîâàíèÿ òðåùèíû. Äàííûé òèï èñïûòàíèé âêëþ÷åí â íîðìàòèâíûå äîêóìåíòû ÏÀÎ «Ãàçïðîì» ñ öåëüþ ïðåäóïðåaeäåíèÿ ðàñïðîñòðàíåíèÿ ïðîòÿaeåííîãî âÿçêîãî ðàçðóøåíèÿ â ìàãèñòðàëüíûõ ãàçîïðîâîäàõ. Îáðàçöû èçãîòîâëåíû èç òðóáû êëàññà ïðî÷íîñòè Ê65 äèàìåòðîì 1420 ìì ñ òîëùèíîé ñòåíêè 27,7 ìì. Êëþ÷åâûå ñëîâà: ïëàñòè÷åñêîå äåôîðìèðîâàíèå, âÿçêîå ðàçðóøåíèå îáðàçöà, ÷èñëåííîå ìîäåëèðîâàíèå, ìîäèôèöèðîâàííàÿ ìîäåëü Ãóðñîíà − Òâåðãààðäà − Íèäåëüìàíà, ñðàâíåíèå ðàñ÷åòà ñ ýêñïåðèìåíòîì.