Application of T-scaling method to account for the continuity of pre-cracked and notched specimen fracture toughness in the ductile-to-brittle transition temperature region

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.

Download Full-text

Experimental Investigation of the Size Effects on the Fracture Toughness and Tearing Modulus

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.33-37.35 ◽

2008 ◽

Vol 33-37 ◽

pp. 35-40

Author(s):

Zhao Xi Wang ◽

Hui Ji Shi ◽

Xiao Liang Zhang

Keyword(s):

Fracture Toughness ◽

Experimental Investigation ◽

Transition Temperature ◽

Size Effects ◽

Stress Triaxiality ◽

Stable Crack Growth ◽

Plane Stress State ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Detailed experiments of fracture toughness in which SENB specimens of five different thicknesses were included were carried out to investigate the size effect in the ductile to brittle transition temperature region. It is found that the fracture toughness of the upper shelf increases with the thickness of the specimens with the similar geometry. While the fracture toughness of the lower shelf decreases with the thickness in the range of 4mm to 12mm and then drops up from 12mm to 16mm with the appearance of shear lips which present the shearing fracture under the plane stress state. The tearing modulus dJ/da which determines the resistance to stable crack growth increases with the increment of thickness and the reduction of the temperature. The results of the stress triaxiality increasing with the reduction of the thickness explain well the experimental results.

Download Full-text

The influence of the out-of- and in-plane constraint on fracture toughness of high strength steel in the ductile to brittle transition temperature range

Engineering Fracture Mechanics ◽

10.1016/j.engfracmech.2015.07.017 ◽

2015 ◽

Vol 147 ◽

pp. 431-448 ◽

Cited By ~ 16

Author(s):

Andrzej Neimitz ◽

Ihor Dzioba

Keyword(s):

Fracture Toughness ◽

Transition Temperature ◽

High Strength Steel ◽

High Strength ◽

Temperature Range ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Download Full-text

Fracture Toughness of Hardox-400 Steel at the Ductile-to-Brittle Transition Temperature Range − The Influence of the In-Plane Constraint

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.224.167 ◽

2014 ◽

Vol 224 ◽

pp. 167-172 ◽

Cited By ~ 2

Author(s):

Andrzej Neimitz ◽

Tadeusz Pala ◽

Ihor Dzioba

Keyword(s):

Fracture Toughness ◽

Transition Temperature ◽

Stress Field ◽

Critical Values ◽

Structural Elements ◽

Engineering Applications ◽

Temperature Range ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Fracture toughness is a structural elements property. Critical values of the J - integral, JIC measured according to the standards requirements, when transferred to engineering applications can lead to a significant conservatism in assessing integrity of a structure. In the article the formulae to estimate the fracture toughness taking into account the in-plane constraint in elements are proposed. These formulae are based on the analysis of the stress field in front of the crack proposed by Hutchinson, Rice and Rosengren (HRR), and O'Dowd's, Shih's modifications of HRR field, as well as the analysis of the stress field in front of the crack, computed numerically.

Download Full-text