Mechanical performance analysis and structural improvement of connection unions for high-pressure manifolds in oil and gas fracturing
HE Yue
CHEN Bo
TAN Shiwu
CHEN Tong
WANG Meiling
Abstract：[Objective]To address the frequent fatigue fracture and corrosive leakage failures of 1502-type connection unions under coupled high internal pressure and intense vibration profiles during hydraulic fracturing operations,a high-fidelity mechanical simulation model was developed to extract the precise structural vulnerabilities and formulate an optimal geometric modifications.[Methods]Firstly,guided by a torque-to-preload conversion formulation,an initial structural preload of 200 kN was implemented in tandem with a maximum field operational internal pressure of 90 MPa.A two-dimensional axisymmetric non-linear finite element model incorporating multi-body sliding friction behaviors was constructed for the FIG.1502 union fabricated from high-strength 40CrNi2Mo steel,wherein a dual-time-step incremental solver was executed to fully replicate the physical sequence of assembly fastening followed by intense fluid loading.Then,based on the structural design philosophy of critical stress relocation,an innovative thread-to-seal misaligned configuration was developed to disengage the co-axial spatial path of the sealing groove and external threads.This design was tightly integrated with an inner diameter reduction from 101.5 mm to 90.3 mm for localized wall reinforcement,an expansion of effective thread counts to 7,and a customized 125° transition slope profile.Finally,full-scale comparative stress simulations and empirical industrial opera-tion trials within the Jimsar oilfield were carried out for engineering validation.[Results]Numerical diagnostics indicate that the peak equivalent von-Mises stress of the original union aggregates at the root of the first thread groove,reaching 559.5 MPa with an extreme stress concentration factor of 5.181,which is the dominant factor leading to fatigue fracture of on-site threads,while the sealing fillet sustains a stress of 244.08 MPa.Implementing the thread-to-seal misalignment configuration effectively shifts the maximum loading burden to the reinforced sealing fillet,cutting the peak global stress down to 175.94 MPa(a 68.6％mitigation)and dropping the global stress concentration factor to 2.199(a 57.6％reduction).Concurrently,the localized maximum thread stress drops to 165 MPa,yielding a highly uniform load distribution across all engaged thread teeth.Field deployment proofs confirm that the optimized connection union operates continuously for over 460 h under a peak pressure of 90 MPa without degradation,demonstrating a 35％improvement in fatigue life compared with the original failed old union.
Keywords：High pressure manifoldConnection unionMechanical performance analysisStructural improvementFracturing operation
Publication Date：2026-06-30
Online Publishing Date：2026-09-12(First online date of this platform, not the publication date of the document)
Pages：9( 150-158 )