Threaded Joint Radial Interference and Shot Peening
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Solution Overview
Problem
Threaded joints in the hydrocarbon industry, particularly in offshore applications, face challenges with fatigue resistance due to environmental stresses from sea movements, leading to potential ruptures and a need for improved design and materials to withstand these stresses.
Innovation Solution
A threaded joint design featuring a male and female tube with specific abutment shoulders, radial interference, and surface treatment like shot peening, combined with optimized thread geometry and surface hardening, to enhance fatigue resistance and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded joint design is used, then the joint can be manufactured and assembled, but the fatigue resistance is insufficient under offshore environmental stresses
Solution Approach 1:
The patent applies different surface treatments to different regions of the threaded joint. Shot peening is applied to the thread roots to create compressive residual stresses, while the thread flanks receive different treatment to optimize friction and wear characteristics. This localized differentiation of surface properties enhances fatigue resistance without compromising the overall structural integrity
Solution Approach 2:
The threaded joint is pre-loaded during assembly to create initial compressive stresses in the threaded connection. This preliminary action ensures that the joint starts in a stress state that resists fatigue cracking, and the pre-load is maintained through the operational life of the connection to prevent rupture under cyclic loading
2Reliability
If shot peening is applied to the threaded joint, then fatigue fracture strength is improved, but the manufacturing complexity increases
Solution Approach 1:
Shot peening is applied selectively only to the thread root regions where fatigue cracks are most likely to initiate, rather than treating the entire threaded joint. This localized application reduces manufacturing complexity and time while maintaining the fatigue strength benefits in the critical areas
Solution Approach 2:
The patent specifies particular parameters for the shot peening process including particle size, shot velocity, and treatment duration to optimize the compressive residual stress profile. By controlling these parameters, the manufacturing process becomes more predictable and easier to implement consistently
3Reliability
If interference fit is increased between thread roots and crests, then radial loads and fatigue resistance are improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies an interference fit parameter where the thread root diameter of one component is made slightly larger than the thread crest diameter of the mating component, creating a controlled interference fit. This parameter is optimized to provide sufficient radial load for fatigue resistance while remaining achievable with standard manufacturing tolerances
Solution Approach 2:
The threaded joint design segments the load-bearing functions: the interference fit between thread roots and crests handles radial loads and fatigue resistance, while the thread flanks handle axial loading. This segmentation allows each interface to be optimized for its specific function without requiring excessive precision across all dimensions
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
The solution significantly increases fatigue life by managing stress concentrations and radial loads, reducing the likelihood of joint failure under operational stresses, and extends the operational life of threaded connections in harsh offshore environments.
Implementation Method 1
the joint has a surface treatment comprising shot peening applied to the beginning and end of the threaded zone of the pin
Data Source
AI summary
A threaded joint has an interference between thread roots of the pin and thread crests of the box of between 1% and 5% of the average thickness of the connection, and a root to load flank radius R in the range of 0.2 mm and 0.4 mm. In other embodiments the interference can be between thread roots of the box and thread crests of the pin. The threaded joint can also have a surface treatment that includes shot peening applied to the beginning and end of the threaded zone of the pin.