Threaded Steel Pipe Residual Stress for Thread Fatigue Resistance
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Solution Overview
Problem
High pressure gas containers face challenges with fatigue fracture in the thread portion of threaded steel pipes or tubes, which can lead to premature failure due to high stress concentrations, especially in high-pressure applications like hydrogen storage containers.
Innovation Solution
Applying specific residual compressive stress to the vicinity of the thread bottom of the threaded steel pipe or tube, either through internal pressure or load application, to offset tensile stress and reduce the risk of fatigue fracture, with conditions ensuring the stress remains within material yield and tensile strength limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If residual compressive stress is applied to the thread portion to improve fatigue strength, then the fatigue life is extended, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by introducing residual compressive stress to the thread portion before the component is put into service. This is achieved through controlled plastic deformation during manufacturing, which creates compressive stresses that will counteract the tensile stresses encountered during fatigue loading, thereby extending fatigue life without requiring additional complex manufacturing steps later
Solution Approach 2:
The patent utilizes parameter changes by modifying the stress state in the thread portion through controlled plastic deformation. By adjusting manufacturing parameters such as pressing force and deformation amount, the residual compressive stress can be optimized to achieve the desired fatigue strength improvement while maintaining manufacturing feasibility
2Reliability
If high internal pressure is applied to generate residual compressive stress in the thread portion, then fatigue strength is improved, but the risk of deformation or fracture increases
Solution Approach 1:
The patent applies local quality by concentrating the plastic deformation and residual compressive stress generation specifically in the thread portion rather than the entire component. This localized approach allows high stresses to be applied where needed to improve fatigue strength while keeping the overall component within safe stress limits, preventing global deformation or fracture
Solution Approach 2:
The patent implements preliminary anti-action by pre-applying compressive stress to the thread portion during manufacturing. This preliminary compressive stress counteracts the tensile stresses that will occur during service, effectively reducing the net stress amplitude and preventing fatigue failure before it can occur during normal operation
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 approach significantly alleviates stress on the thread portion, enhancing the fatigue life and allowing for higher pressure and larger cross-sectional usage of threaded steel pipes or tubes without the risk of deformation or fracture.
Implementation Method 1
a maximum value of residual compressive stress at a position of 0.4 mm in a depth direction from a thread bottom of the female thread portion is 100 MPa or more and less than or equal to tensile strength
Data Source
AI summary
To alleviate stress exerted on a thread portion of a threaded steel pipe or tube during use to prevent fatigue fracture, there is provided a threaded steel pipe or tube having a female thread portion on an inner peripheral surface of at least one end, wherein a maximum value of residual compressive stress at a position of 0.4 mm in a depth direction from a thread bottom of the female thread portion is 100 MPa or more and less than or equal to tensile strength of a material of the threaded steel pipe or tube.