Introduction: In this paper, we focus on the contact pressure distribution and circumferential stiffness of flange-spigot connections in pipeline systems. The aim is to develop a theoretical model that accurately predicts the behavior of these connections under various loading conditions. This study is important because the failure of pipeline connections can have serious consequences, both in terms of safety and economic costs.
Overview: The flange-spigot connection is a widely used joint in pipeline systems due to its ease of installation and maintenance. However, the contact pressure distribution between the flange and spigot surfaces plays a critical role in determining the overall strength and stiffness of the joint. In this section, we provide an overview of our research approach and objectives.
2.1 Simplified analysis of flange-spigot structure: To understand the contact pressure distribution in flange-spigot connections, we first conduct a simplified analysis of the structure. This involves modeling the connection as a series of sub-regions with different mechanical properties.
2.2 Sub-region division of flange bearing surface: We divide the flange bearing surface into multiple sub-regions to account for variations in material properties and loading conditions. We also consider how each bolt affects the contact pressure distribution within its influence zone.
2.2.1 Model of one bolted region under axial load: To better understand how bolts affect contact pressure distribution, we create a model for a single bolted region under axial load. This helps us to determine how much stress each bolt contributes to overall joint strength.
2.2.2 Contact pressure distribution considering the bolt influence zone: By considering the influence zone around each bolt, we can more accurately predict how stress is distributed across the entire flange surface.
2.3 Sub-region division of spigot overfill surface: We also divide the spigot overfill surface into multiple sub-regions to account for variations in material properties and loading conditions. We consider how the gap at the root of the spigot affects contact pressure distribution.
2.3.1 Model under spigot overfill constraint: To better understand how the spigot overfill constraint affects contact pressure distribution, we create a model for a single sub-region. This helps us to determine how much stress is transmitted through the spigot surface.
2.3.2 Contact pressure distribution considering the gap at the root of spigot: By considering the gap at the root of the spigot, we can more accurately predict how stress is distributed across the entire spigot surface.
- Circumferential stiffness model:
In this section, we propose a circumferential stiffness model for flange-spigot connections based on fractal contact theory and discretized Iwan models.
3.1 Fractal contact model: We first introduce a fractal contact model to describe asperity interactions between surfaces in contact. This involves modeling each asperity as an elastic-plastic spring with varying properties depending on its location and orientation.
3.1.1 Contact modeling of asperity: We explore three types of contact behavior: purely elastic, purely plastic, and elastoplastic.
(1) Purely elastic contact: In this scenario, no plastic deformation occurs between contacting surfaces.
(2) Purely plastic contact: In this scenario, all deformation is assumed to be plastic.
(3) Elastoplastic contact: In this scenario, both elastic and plastic deformation occur during contact.
3.1.2 Parameters of the sub-regions: We determine mechanical states and real-contact areas for each sub-region to improve accuracy when predicting stress distributions across flange-spigot connections.
3.2 Discretized Iwan model: We use a discretized Iwan model to describe tangential frictional forces between contacting surfaces in our circumferential stiffness model.
3.2.1 Determination of parameters in the Jenkins element: We use a Jenkins element to describe the contact behavior between each sub-region and its neighboring regions, determining its parameters to account for variations in material properties.
3.2.2 Tangential response of Iwan model: Finally, we describe how tangential forces are transferred between neighboring sub-regions based on the Iwan model.
- Case study and discussion:
To validate our theoretical model, we conduct a case study comparing predicted stress distributions with experimental results from flange-spigot connections under various loading conditions. We also discuss limitations and potential applications of our model in engineering design and analysis.
- Validity verification of theoretical model:
This section presents our validation approach and results for our proposed theoretical model using finite element analysis (FEA) simulations. We compare the FEA results with both analytical solutions and experimental data to demonstrate the accuracy of our proposed method. We also highlight the limitations and assumptions made in this study that may affect the validity of our proposed theoretical model in certain scenarios.
