After two years of operation, condensate recycle line at a natural gas production field was failed due to fatigue cracking. Fatigue was caused by combination of both cyclic stresses related to intermitted operation mode and stress concentration at base of fillet weld. Stress concentration was remarkably increased as a result of weld surface defects including undercut and overlap that caused sharp transition at fillet weld base. Internal welding defects such as porosity and lack of fusion could not played a role in crack formation. On the other and, failure could be encouraged by corrosion after exposing of crack surface to atmospheric condition. The problem has been solved by improving geometry of fillet weld so that, acceptable contouring with smooth transition at fillet weld base was obtained that in turn resulted in reducing stress concentration. Periodic inspection was scheduled to check the existence of outer surface cracks and necessary action to be done in order to avoid sudden failure and unexpected shut down.
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