Weld-induced residual stresses in a prototype dragline cluster and comparison with design codes

The Australian coal mining industry employs a large fleet of thin-walled Circular Hollow Section (CHS) welded draglines built of several clusters along the length of the main boom, which are often very heavily overlapped with co-eccentric multiple tubular structures. Heat treatment processes for relieving thermally generated weld-induced residual stresses are usually not employed owing to the high costs and potential dragline downtime. However, it is estimated that these weld-induced residual stresses are usually within a tolerable range and are not the major motivating factor in the initiation and propagation of fatigue-induced cracking. This paper presents the simulation of welding-induced residual stresses in a CHS T-Joint, which would form the first of the four lacings welded on to the main chord of a typical mining dragline cluster. The paper compares numerically generated residual stresses during the welding process in a single weld pass with the approach used in two Standards: (i) R6-Revision 4, Assessment of the Integrity of Structures Containing Defects and (ii) American Petroleum Institute API 579-1/ ASME FFS-1 2007. The comparison attests to the observation that while residual stresses in the fused area at some points could be higher than the yield stress, they are generally not capable of inducing cracks in their own right.