Fracture Toughness of Electrogas Welds in Double-hull Construction PDF Download

Author: Eric James Kaufmann
Publisher:
ISBN:
Category : Fracture mechanics
Languages : en
Pages : 54

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Book Description
Abstract: "A new tanker design currently under development incorporates new design and fabrication features which are expected to reduce shipbuilding costs by as much as 30 percent and provide for environmentally safe transport of oil products. This new double-hull design incorporates 2.1 m x 2.4 m x 15.2 m (7'x8'x50') cellular modules joined into 172-268 metric ton (190-295 ton) hull sub-assemblies. The sub- assemblies can be incorporated into new or existing single-hulled ships. As currently planned, the two hull plates and cell web girder of each module will be joined with a single, continuous weld pass in a vertical orientation using the Electrogas welding (EGW) process. The EGW process was selected because of the high deposition rates which can be achieved (23 kg/hr) and corresponding high productivity. Because of uncertainties associated with the weld process stemming from experiences with the related electroslag welding (ESW) process regarding fatigue and low fracture toughness, studies were undertaken to evaluate the fatigue and fracture behavior of this weld detail. The results of the fatigue study were reported previously. The current study is a follow-on which examines the fracture toughness of the electrogas weld metal. Elastic-plastic fracture toughness (J[subscript IC]) and Charpy V-notch (CVN) impact toughness tests were performed on a test plate fabricated using the same materials and weld procedures as used in full-size fabrications. Compact tension (CT) and Charpy V-notch test specimens were fabricated from the weld metal in the L-T and T-L orientation. Additional test specimens were located in the heat-affected-zone (HAZ) and base plate (ABS Grade CS). A total of 12 compact tension specimens and 72 CVN specimens were tested. Test results from both compact tension and CVN tests indicate that the fracture toughness of the base metal, weld metal and HAZ were similar. The CVN tests indicated a 20 J (15 ft-lb) transition temperature of at least -40 C. The J[subscript IC] tests performed in accordance with ASTM E 813 resulted in J[subscript IC] values in the weld metal and HAZ ranging from 106-146 kJ/m2 (608-834 in-lb/in2) which correlate to K[subscript c] values of 148- 174 MPa(m)[superscript 1/2] (135-158 ksi(in)[superscript 1/2]). No significant orientation effect was observed in the weld metal. Based upon the types and sizes of fabrication flaws observed in the previous fatigue study, an assessment of their fracture sensitivity was performed in light of the measured fracture toughness. It was concluded that none of the observed fabrication flaws were critical from a fracture viewpoint and that critical flaw sizes were through-thickness and large enough to be detected by visual inspection."