Investigating the fracture behaviour of X70M linepipe steel girth weldments via single edge notched tension and bend tests

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2018

Öğrenci: UYGAR TOSUN

Danışman: CEMİL HAKAN GÜR

Özet:

Increasing competition in the global market motivates the producers to invest in novel and cost-effective manufacturing technologies in pipeline construction. Gas metal arc welding multi-pass process has been proven for as-rolled low-alloy steels. Engineering of welding is a special concern in terms of fracture mechanics because the joint yields a fusion line between chemically and physically dissimilar structures. Engineering Critical Assessments (ECA) suggest more realistic scenarios for material’s elastic-plastic behaviors at proximity of the discontinuities compared to conventional good workmanship criterion, and thus lower the repair rates dramatically by allowing more generous discontinuity dimensions. In this study, fracture toughness parameters and properties affecting the fracture behavior of as-welded API 5L X70M steels were investigated. After validating the integrity of girth welds with conventional non-destructive and destructive tests, Single Edge Notched Tension (SENT) and Single Edge Notched Bend (SENB) tests were performed to obtain single critical values and tear resistance curves. The fracture surfaces were examined. Then, the effects of crack tip constraint and plastic deformation were investigated. The results show that, the SENT specimens demonstrate better resistance to both located crack and propagation of tearing compared to SENB specimens due to lower crack tip constraint.