Fatigue failure of threaded connections used in pipe joints, especially in the oil industry can be very costly. Stress analysis of threaded connections is difficult because of the varying contributions of tooth geometry, tooth stiffness and overall connection stiffness, and the role of pre-load. Finite Element Analysis of the complete joint it usually time-consuming and expensive due to the complexity of the mesh and size of the mesh data. This paper proposes a hybrid model which is used in conjunction with a substructure finite element model to study the way m Which loads and stresses are distributed over the threads of a screw coupling.
The determination of thread loads and root stresses is a fundamental requirement m the design of threaded connections. The complexity of the geometry together with other factors such as the contribution of pre-load and different modes of external loading make. the task of the analysis of threaded connections very complicated. The main techniques used for analysing the load or stress distribution along threaded connections have mainly been experimental, analytical or numerical. Experimental work. and, in particular the 3-D photo-elastic methods Which use a stress freezing technique, require specialist facilities and tend to be expenslve and time-consuming. The analytical solutions available for load distribution along threaded connections have proved to be useful. However, the main drawback with these solution is the fact that they are usually driven on the basis of fairly drastic assumptions and simplifications of thread geometries. In numerical approach, finite element analysis of an axisymmetric full model or a three-dimensional model of the joint is used. Although this method has proved to be very useful for analysis of particular thread geometries, but preparing different full F.E. models in particular when parametric studies are being called out have proved.
