EVALUATION OF LOCAL BRITTLE ZONES USING THE FINITE-ELEMENT METHOD

The existence of local brittle zone (LBZ) in multipass C-Mn microalloyed steel welds has caused a great deal of concern to the offshore industries. A number of fracture toughness studies revealed the presence oi LBZ in the coarse; grained weld heat-affected zone (HAZ) of multipass welds. Although the HAZ toughness in LBZ can be very low, whether the low value of fracture toughness is detrimental to the structural integrity is not well understood. This paper describes the effect of the LBZ size on the resistance to fracture of the specimen using the elastic-plastic finite element method. The crack tip opening displacement (CTOD) criterion was used to evaluate the crack stability and arrest behaviors. Plastic zones emanating from both crack lip and LBZ interface were plotted for various combinations of base metal (EM) and LBZ sizes in order to characterize the specimen. A threshold LBZ size under which a crack extended initially in the LBZ, but would arrest at the interface of LBZ and BM due to tougher surrounding base metal, was also discussed

Design analysis for welding of heavy W shapes

An investigation evaluated the effects of welding parameters and joint geometry on the magnitude and distribution of residual stresses on thick-section butt joint

DETERMINATION OF RESIDUAL-STRESSES IN THICK-SECTION WELDMENTS

The purpose of this study is to develop an analytical method for predicting through thickness distribution of residual stresses in a thick plate with a multipass welding process. The analysis was carried out in two steps. The first step was to develop a thermal model for heat flow analysis in a two-dimensional cross-section of the plate. For a modeling of the heat input to the cross-section, a ramp heat input was used to avoid numerical instability and to include the effect of a moving arc. The best ramp time was selected by an analysis of the root pass on a 1/2-in. (1 2.7-mm) thick plate and comparing it with experiments. The next step was to develop a structural model to predict stress distribution using the thermal loading obtained in the first step. A generalized plane strain assumption was used in the stress analysis. A lumped pass model was developed to reduce the total computational time and cost. Each layer of weld bead was assumed as one lumped pass in this model. The heat input for every pass in that layer was added and applied on the top surface of a weld layer. The results by the lumped model showed good agreement with the experiment and the results of another model, which analyzed every weld pass separately

WELDING RESEARCH Fitness-for-Service Design for Underwater Wet Welds A unique flexible connection for underwater welding repair is tested for performance

ABSTRACT. This paper presents a new concept of improving the use of wet welds for underwater structure repair or construction. A flexible intermediate connection pad, prefabricated on land and welded to the structural members in wet condition, cushions the stresses on joints. The inherently inferior impact property of the wet weldment can be coped with proper design of this cushion pad. The wet welded joint can therefore fit its designed purpose. In this study, both design analysis and experimental tests were conducted to demonstrate the design solution using the cushion pad. A statistical data base on wet weld properties was first developed to define the performance level of wet welds. The fitness for service of the flexible connection was evaluated by impact testing. The results show that the performance level of the connection can be improved through proper design regardless of the low toughness of the wet weldment