Wellhead Flange Failure Analysis and Composite Load-Bearing Capacity Under Ultrahigh Pressure

Summary As the wellhead pressure escalates, wellhead equipment is confronted with a series of significant challenges that impose increasingly stringent demands on the performance and reliability of wellhead flanges. Given the current absence of design guidelines for ultrahigh pressure (UHP) wellhead equipment rated at 175 MPa, we introduces a methodology for determining design parameters for nonstandard UHP wellhead flanges, leveraging the existing API SPEC 6A standards. The reliability of the calculation results of the finite element model (FEM) based on the elastic-plastic constitutive model was verified through the analytical model and experimental testing. The structural integrity analysis of the nonstandard flange was carried out using the finite element analysis (FEA) method. The results show that the stress check of the flange meets the API criteria, and the contact pressure is at least 4.5 times the design pressure, which provides a design reference for the development of UHP nonstandard flanges. Further, the effects of the deterioration of lubrication conditions and bolt pretightening on the sealing performance that may occur in actual engineering are explored. In addition, the load-capacity line set of the nonstandard flange is computed using the composite load-bearing-capacity line-set-determination approach derived from the API TR 6AF2 leakage criteria. The calculation results of the extreme working conditions on the line set show that the sealing contact still has more than three times the contact pressure. This study enhances and further refines the sealing design methodology for 175-MPa UHP wellhead flanges and provides a reference for determining the allowable loads under composite loading conditions for wellhead flanges in UHP.