TWI Industrial Member Report Summary 279/1985
By S J Maddox
There is a need to establish a method for the derivation of acceptance levels for misalignment in welded joints based on fitness-for-purpose. The intention is to introduce such recommendations into BS PD 6493. In addition, a subcommittee of Commission XIII of the International Institute of Welding is considering the introduction of such recommendations. The present report is a review of available information on the effect of axial and angular misalignment in butt joints in flat plates and in pressurised vessels. The information suggests that the main effect of misalignment is to introduce secondary bending stresses when the joint is subjected to axial loading. For many configurations, these stresses can be calculated using simple expressions to give an effective stress concentration factor KI. Fatigue data for butt joints containing axial or angular misalignment were successfully correlated with data from aligned joints using KI x nominal applied stress range. It is recommended that allowance should be made for misalignments which are likely to arise during fabrication at the design stage by using KI to reduce design stresses accordingly.