Joint Strength or "Efficiency" Factors of Steel Lap Welded Joints for Use in Water Conveyance

Joint "efficiency" factors are proposed for pressure vessels, piping, and pipelines by ASME standards. For the particular case of non-radiographically-tested lap-welded joints, a low value of joint "efficiency" is proposed. This low value has raised some concerns regarding the use of welded lap joints in geohazard or seismic areas, where significant axial stresses and strains are developed, as a result of ground movement. The paper discusses the joint efficiency concept, mainly in relation with the corresponding failure mode of the pipeline, based on recent experimental observations and numerical simulations. The conservativeness of the ASME "joint efficiency" values for lap-welded joints is demonstrated. Furthermore, based on experimental evidence, it is shown that lap welded joints can sustain significant deformation, without loss of pressure containment. The conclusions from this paper support the argument that lap welded joints constitute a simple, efficient, and economical solution for pipeline joints in seismic areas. © 2019 American Society of Civil Engineers

Experimental Investigation of Steel Lap Welded Pipe Joint Performance under Severe Axial Loading Conditions in Seismic or Geohazard Areas

Welded lap joints are commonly used in large-diameter steel pipelines for water transmission. Their structural performance constitutes a key consideration for safeguarding pipeline integrity with no loss of pressure containment, required after a severe seismic or geohazard event. Full-scale experiments are presented, which are part of an extensive ongoing project related to structural performance of welded lap joints under severe ground-induced (seismic) actions. The paper describes a series of large-scale physical experiments on 24-in. diameter steel pipes with welded lap joints subjected to axial compression and tension. The axial loading experiments under consideration complement the series of large-scale bending tests performed in 2017, and presented in the ASCE 2018 Pipelines Conference (paper entitled: "Experimental Results of Steel Lap Welded Joints in Seismic Conditions", authored by Keil et al.). The specimens tested under axial loading are first pressurized to 40% of yield pressure, and subsequently subjected to large amount of compression or tension. Measurements of the axial load, characteristic displacements, and local strains at the joint area have been obtained. All specimens exhibited the capability of sustaining high axial loads with significant axial deformation, without loss of pressure containment. In support of the above experiments, advanced finite element models have also been developed, for the purpose of simulating the experiments and elucidating some pertinent topics on the structural response of welded lap joint behavior. The results of the present study demonstrate the remarkable strength and deformation capacity of lap welded joints under consideration, supporting the argument that those joints can be used in steel pipelines crossing seismic and geohazard areas, where severe and permanent ground-induced actions are expected. © 2020 American Society of Civil Engineers