In-service Relocation of 24 inch Wet Acid Flare Line Header
Proceedings Publication Date
One of the major problems in the South Pars Gas Complex is dislocation and abnormal movement of bi-phase fluid lines, the major problem happened during gas plant overhaul 2007 in 24 inch wet acid gas flare line header. The middle of the last loop, had a 356mm deviation from original position and fallen from the pipe-rack structure and its support caught by beam wedge. Therefore, pipeline was distorted and was under stress in bends and supports. In this paper, our method of safe in-service relocation of this pipeline and the reason of dislocation is presented. For ascertaining the nature of the failure, two assumptions were examined, thermal shock and differential shock. The result shown it should be the aftermath of differential shock. To avoid unnecessary rehabilitation, the significance of defects detected in the pipeline was assessed. For this purpose operating condition and also induced stresses and deflection profiles of dislocation were applied in the finite element model, the result shown max available stress is nearly closed to the yield stress, but it might exceed beyond the elasticity limit of pipe material. It could have resulted in not only decrease pipeline stability and plant reliability, but also possible injury to plant personnel. Thus, relocation was urgent. After job risk assessment Executive procedure was performed in the three steps; first, preparation, the internal operating pressure of the pipeline reduced, the loop was restrained in three dimensions by forces extracted from FEM, to prevent sudden movement; Second was removing the source of stress by cutting the caught part of support. Third, removing forces by releasing chain-block slowly, consequently line was returning slowly to its original place, safe, cost-effective without loss of service. NDT was done for girth welds and supports weld connected to the pipeline.