Structural Study Ovality Effect in an Incoloy 800 Nonlinear Pipe Bend

Pipe bends construct an integral part of any piping system in the industrial field. During an industrial operation does happen. Catastrophic failures in the extrados of pipe bend are identified. It is very essential to identify the potential cause of such a failure and to provide a suitable solution by considering the minimum design requirements. Significant researches have been carried out on the subject of construction of an integrity assessment for pipe bends using both analytical and experimental approaches. Many researches were focused on handling the problem of pipe bends with uniform cross section. This study focuses on an oval cross section. It is difficult to avoid thickening and thinning on the inner and outer radius of the pipe during the manufacturing of inlet pipe bends. The cross section of the bend becomes non circular and the non-circular cross section acceptability is based on the induced level of shape irregularity. Moreover, In most of the investigations, the geometric shape (ovality) and its effect due to various loding conditions have not been subjected to thorough investigation. Hence it requires a detailed investigation which has been carried out the present work. The effect of ovality in pipe bend region is the primary objective of this study. Finite Element Analysis (FEA) has been performed for different pipe bend geometry process using ANSYS-work bench. Experimental evaluation was carried out for validating FEA results. A pipe with 90° bend geometry along with attached straight pipe was considered for the study. Analyses were performed by varying the percent of ovality (Co) between 0 and 20. The study was carried out considering (a). Pure internal pressure (b) pure bending and (c) Combined internal pressure and in-plane bending for various r/t values ranging from 10 - 50.   The modeling procedures of pipe bend using CREO have been found to be acceptable based on FEA results obtained which are in line with the existing literature results. The results of these studies have been presented in the form of load-deflection plots, for the stated loading conditions. The limit pressure and moments of each case has been obtained from the load deformation curves. The results of the investigation show the significance of geometric shape irregularity (ovality) while calculating the stresses of the pipe bends. Increase in the in-plane moment, shows the effect of deformation as high in extrados of pipe bend geometry when compared to the intrados. When loading the in-plane moment and internal pressure on thin walled pipe bend, a considerable cross sectional ovalization is observed which actually affects the load carrying capacity? The deformation and the induced Von-Mises stresses of the different pipe bend geometry were noted for the purpose of quantifying the load carrying capacity. For the given loading conditions, the interaction of the same is significantly affected by r/t. Rayleigh-Ritz analysis was used for the development of a correlation between the allowable pressure ratio and various design parameters including ovality based on the results obtained in the FEA Analysis.  Based on the results obtained from the specified design conditions, the criteria of ovality limit and the structural integrity of pipe bends can be determined and this will reduce the rate of rejection of the pipe bends to a greater extend.  In this proposed method, the importance of the effect of internal pressure, elevated temperature and percentage ovality on induced stress, strain in the pipe bend geometry is investigate. The analysis aims to retain the pipe quality and reliability in a pipe bend.