An Investigation of Stresses in Bolted Connectors for Marine Risers

This paper presents a procedure on the finite element method for analyzing a bolted flange connector and compares this method with three traditional approaches. The finite element method considers such effects as flange interface separation, nonlinear and nonconstant flange stiffness, and bolt bending. A comparison of the finite element model with the three traditional methods (each employs a formula for flange stiffness) shows a fairly close correlation for total bolt force versus applied load, but a wide discrepancy for maximum bolt stress versus applied load. The discrepancy between the finite element model analysis and the three other methods (empirical by Weiss and Wallner, truncated conical area by Roetscher, and the classical hollow cylinder approach) can be attributed to the change in flange stiffness during separation and the occurrence of bolt bending. The selected method of analysis was shown to significantly affect the results of a bolt fatigue analysis, but was shown to have little effect on a static analysis. In offshore applications, the environment creates dynamic stresses which make a fatigue analysis essential for long-term safety.