Experimental assessment of cracked tubular joints repaired with crack-deflecting holes and weld-toe grinding
Master thesis
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https://hdl.handle.net/11250/3134163Utgivelsesdato
2023Metadata
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Sammendrag
Fatigue-induced cracks in tubular joints represent one of the major threats to the structuralintegrity of offshore infrastructure. Consequently, developing and researching efficienttemporary and permanent repair solutions is essential. Investigation of various technics andmethods is ongoing, and the recent advancement in the exploration of crack deflection holes incombination with weld-toe grinding has made a foundation for further investigation of themethod.This thesis investigates the effectiveness of delaying crack propagation in tubular jointssubjected to high cycle fatigue with crack-deflecting holes combined with weld-toe grinding.Furthermore, a numerical analysis has been conducted to facilitate a better comprehension ofthe stress field and stress evolution inherent in the experimental work.One tubular double T joint was tested experimentally through a three-phased testing scheme.In the initial phase, the specimen underwent cyclic axial loading yielding stresses within thehigh cycle fatigue regime to the point of achieving a through-thickness crack. The load rangethroughout the pre-cracking phase was maintained constant with an R-ratio of 0.1. During thisphase, an investigation of the stress concentration factor of the intact specimen was also carriedout. The next phase of the testing program comprised repairing the cracked specimen by theuse of crack-deflecting holes. These crack-deflecting holes were drilled in the crack tipproximity, and the weld toe behind the drilled hole was ground according to DNV-RP-C203and BS 7608 specifications. In the final testing phase, the performances of the repairedspecimen were investigated by subjecting the specimen to further cyclic loading. As the crackinduces higher stress concentrations, the load range was reduced to keep the stress levels withinthe parameters of high cycle fatigue. Upon attaining a clear indication of enhanced fatigueendurance post-repair, the load range was significantly increased to facilitate the examinationof subsequent crack initiation and propagation.In this study, the crack was successfully arrested in the crack-deflecting holes. Furthermore, therepair method indicated an apparent enhancement of the fatigue endurance of cracked tubularjoints subjected to stress ranges within the high-cycle fatigue regime. Finally, the recentdiscovery of reverse coalescence in conjunction with crack initiation after repair with crackdeflecting holes was confirmed for both hole reparations in the experimental work. Although asingle test is not a proof of anything in fatigue, the results are promising and may justify furtherinvestigation.