615 Applicability of the (4δ_t, σ_<22c>) Criterion to Predict the Test Specimen Thickness Size on the Fracture Toughness of a Material in the Ductile-to-Brittle Transition Temperature Region for A533 Grade B

This work was motivated by the fact that although fracture toughness of a material in the ductile-to-brittle transition temperature regionJcexhibits the test specimen thickness (TST) effect onJc, frequently described asJc∝(TST)-1/2, experiences a contradiction that is deduced from this empirical formulation; that is,Jc= 0 for large TST. On the other hand, our previous works have showed that the TST effect onJccould be explained as a difference in the out-of-plane constraint and correlated with the out-of-planeT33-stress. Thus, in this work, the TST effect onJcfor the decommissioned Shoreham reactor vessel steel A533B was demonstrated from the standpoint of out-of-plane constraint. The results validated thatT33was effective for describing theJcdecreasing tendency. Because the Shoreham data included a lower boundJcfor increasing TST, a new finding was made thatT33successfully predicted the lower bound ofJcwith increasing TST. This lower boundJcprediction withT33conquered the contradiction that the empiricalJc∝(TST)-1/2predictsJc= 0 for large TST.

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A failure criterion to explain the test specimen thickness effect on fracture toughness in the transition temperature region

Engineering Fracture Mechanics ◽

10.1016/j.engfracmech.2013.03.025 ◽

2013 ◽

Vol 104 ◽

pp. 184-197 ◽

Cited By ~ 34

Author(s):

Toshiyuki Meshii ◽

Kai Lu ◽

Ryota Takamura

Keyword(s):

Fracture Toughness ◽

Transition Temperature ◽

Temperature Region ◽

Failure Criterion ◽

Test Specimen ◽

Thickness Effect ◽

Specimen Thickness

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Variables Affecting Fracture Toughness of Welds in T-K-Y Connections

Volume 5: Materials Technology; Petroleum Technology ◽

10.1115/omae2014-24205 ◽

2014 ◽

Author(s):

Radhika Panday ◽

Shenjia Zhang ◽

Jon Ogborn ◽

Badri K. Narayanan

Keyword(s):

Heat Treatment ◽

Fracture Toughness ◽

Transition Temperature ◽

Weld Metal ◽

Welding Process ◽

Post Weld Heat Treatment ◽

Factors Affecting ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Fracture toughness of tubular welded joints is one of the critical factors affecting the structural integrity and reliability of offshore structures, such as platforms and subsea pipelines. The factors affecting the design fracture toughness of these structures are related to, both, the welding process as well as the chemical composition of the weld metal. The welding process in this application typically comprises of depositing weld metal in the tubular joints of varying thicknesses through series of weld passes. The number of weld passes required for welding these joints subjects the weld metal to repetitive cycles of heating and cooling. The effect of the thermal cycling introduces significant heterogeneity in the microstructure. This is further exacerbated by the presence of micro-alloying elements such as Niobium (Nb) and Vanadium (V) that form complex carbides, nitrides and carbo-nitrides during post weld heat treatment (PWHT). The focus of this work is to evaluate the effect of micro-alloying elements on the ductile to brittle transition temperature and the mode of fracture at temperatures relevant to offshore applications. A threshold Nb and V level has been determined for achieving acceptable weld metal toughness. The improvement in the fracture toughness using this approach has been quantified by Charpy V-Notch (CVN) and Crack Tip Opening Displacement (CTOD) measurements. The Ductile to Brittle Transition Temperature (DBTT) has been shown to be shifted to lower temperatures by 25 °C after post weld heat treatment in the welds where the total amount of Nb and V are controlled to less than 40 ppm. A wet precipitate extraction technique was used to extract precipitates from the welds to establish the presence of fine Nb rich precipitates in the welds with the higher DBTT. The weld deposited with controlled levels of Nb and V was further tested in different joint configurations and base plate thickness. The fracture toughness was evaluated by CTOD testing of the weld in two different thicknesses (50 mm and 70 mm). Increased specimen thickness resulted in lower CTOD values.

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