AN EXPERIMENTAL RIG FOR VERIFICATION OF THE MECHANICAL PROPERTIES OF WELDS PRODUCED AT IN-SERVICE WELDING

摘要

The strength of a weld joint is determined by its geometry and its metallurgic structure, which is dependent on the cooling rate, its chemical composition and the original grain size of the base material. During in-service welding of structures affected by a forced flow of fluid on its reversed side the cooling rate depends on the fluid's boundary layer, the material's thickness and the heat input of the welding process. Currently, the calculation of the cooling rate during in-service welding is made by means of numerical methods such as the Finite Element Method, FEM. Through the introduction of an apparent thermal conductivity, k_(PL), it possible to determine the cooling rate for specific welding parameters by means of Rosenthal's equation. This can be done with a standard pocket calculator. An experimental rig for measurement of the heat transfer during the in-service welding of structures affected by a forced flow of fluid on its reversed side has been designed and built. The physical principles of welding on plates affected by a forced flow of fluid on their reverse side are the same as for welding on the circumference of a pipe containing a forced flow of fluid. In the rig, the required boundary layer is built up in a pipe system by means of a pump. As the flow and the temperature of the fluid can be controlled to simulate the specific heat transfer, it is now possible to verify the values of the apparent thermal conductivity, k_(PL), that were calculated by means of FEM. A quantitative database will be filled with values of the apparent thermal conductivity, k_(PL), for various configurations. For the purpose of evaluation and qualification of in-service Welding Procedures Specifications, WPS, the sponsors of the research project use the experimental rig.