Wellhead Load Capacity Calculation via Radial Deflection
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Solution Overview
Problem
Existing wellhead systems face challenges in accurately calculating the load capacity due to non-ideal smooth surfaces and manufacturing tolerances at the interface between inner and outer casings, which affect contact stresses and overall system reliability.
Innovation Solution
A method is developed to calculate the load capacity of a wellhead system by determining contact stresses at specific interfaces using radial deflections and axial movements of components, taking into account the tapered surfaces and ridged profiles of the tubular members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional friction grip clamping systems are used with non-ideal smooth surfaces and manufacturing tolerances, then the system allows for ease of assembly and adjustment, but the contact stress calculation becomes inaccurate and load capacity is compromised
Solution Approach 1:
The patent transforms the contact stress calculation from a simple point-contact model to a distributed pressure model that accounts for surface irregularities and manufacturing tolerances. By integrating pressure distribution across the entire contact area and considering radial deflections, the calculation accurately reflects real-world conditions while maintaining ease of assembly.
Solution Approach 2:
The patent performs preliminary radial deflection analysis of both the annular component and collar before finalizing the contact stress calculation. This preliminary action accounts for elastic deformation that occurs during assembly, ensuring that the load capacity calculation reflects the actual stressed state rather than assuming rigid bodies.
2Measurement precision
If a clamping system with tapered surfaces and radial deflection is used, then the grip force and contact stress can be accurately determined, but the calculation complexity increases due to multiple interfaces and deflection equations
Solution Approach 1:
The patent divides the clamping system into distinct segments (annular component, collar, inner tubular member) and analyzes each interface separately. By segmenting the calculation into radial deflection of the annular component, radial deflection of the collar, and contact stress at each interface, the complex multi-interface problem becomes manageable while maintaining high measurement precision.
Solution Approach 2:
The patent uses radial deflection as an intermediary parameter to connect the geometric parameters (tapered surfaces, gap dimensions) with the final contact stress calculation. This intermediary approach simplifies the overall calculation by providing a clear causal chain: axial load → radial deflection → contact stress → load capacity.
3Force
If the collar is designed with negligible hoop stiffness to allow radial distortion, then the clamping force can be effectively applied, but the structural integrity and stability of the collar may be compromised
Solution Approach 1:
The patent applies local quality by allowing the collar to have different stiffness characteristics in different directions and locations. The collar is designed with sufficient radial flexibility to allow distortion under axial load for effective clamping, while maintaining adequate tangential stiffness to preserve structural stability. This localized differentiation of mechanical properties resolves the contradiction between clamping force application and structural integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for precise determination of contact stresses and load capacity, enhancing the reliability and safety of wellhead systems by accounting for manufacturing tolerances and surface irregularities.
Implementation Method 1
the tapered surface of the annular component exerts sufficient radial force to distort the collar inwardly in order to grip an inner tubular member
Implementation Method 2
the inner tubular member having an outer surface including a ridged profile
Data Source
AI summary
The present invention provides a method of calculating the load capacity of a wellhead system. The method comprises determining a first contact stress at a first interface between an annular component and a collar and equating a radial deflection of an inner surface of the annular component with a radial deflection of an outer surface of the collar. The method uses a first contact stress and the axial movement of the annular component to determine a contact stress at a gripping interface between a gripping surface and an inner tubular member. The method also equates a radial deflection of the outer surface of the inner tubular member with (i) a radial deflection of the gripping surface plus (ii) a depth of penetration of a ridge of the outer surface of the inner tubular member into the gripping surface (iii) a radial dimension of an initial gap between the outer surface of the inner tubular member and the inner surface of the outer tubular member.