Two-Step Steel Pipe Thread Connection for Seal Interference Control
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Solution Overview
Problem
In threaded connections for steel pipes with two-step thread construction and intermediate seals, the ratio of critical cross-sectional areas affects sealability and tensile strength, leading to variations in seal interference and rigidity, which can result in reduced sealability and increased likelihood of deformation under complex loads.
Innovation Solution
A threaded connection design where the pin and box have specific relationships between their intermediate critical cross-sectional areas, ensuring PICCSA+BICCSA > BCCSA and 0.70 ≤ PICCSA/BICCSA ≤ 0.95, with tapered threads and shoulder surfaces to maintain optimal seal interference and tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the intermediate critical cross-sectional areas of pin and box are not optimally proportioned, then manufacturing is simpler, but sealability deteriorates and deformation occurs under load
Solution Approach 1:
The patent applies parameter changes by establishing specific mathematical relationships between the intermediate critical cross-sectional areas (PICCSA and BICCSA) of the pin and box. The invention defines that PICCSA+BICCSA > BCCSA and 0.70 ≤ PICCSA/BICCSA ≤ 0.95, transforming the design from qualitative to quantitative parameter control. This ensures optimal sealability and load-bearing performance without excessive complexity.
2Strength
If PICCSA is too large, then pin rigidity improves, but box deformation increases and sealability deteriorates
Solution Approach 1:
The patent resolves this contradiction by defining the optimal parameter range for PICCSA/BICCSA ratio between 0.70 and 0.95. This quantitative parameter control ensures that the pin maintains sufficient rigidity while the box maintains adequate strength, preventing excessive deformation and ensuring sealability under complex loads.
Solution Approach 2:
The invention effectively creates a composite structural system where the pin and box work together as an integrated load-bearing assembly. By optimizing the ratio of their intermediate critical cross-sectional areas, the design achieves synergistic performance where neither component becomes the weak link, maintaining both rigidity and sealability.
3Strength
If PICCSA is too small, then pin deformation increases, but box strength is improved, however sealability deteriorates due to displacement
Solution Approach 1:
The patent resolves this contradiction by establishing the lower bound of the PICCSA/BICCSA ratio at 0.70. This ensures that the pin intermediate critical cross-sectional area is sufficiently large to prevent excessive deformation while maintaining the box's strength. The quantitative parameter control prevents the displacement that would compromise sealability.
4Area of stationary object
If the sum PICCSA+BICCSA is too small, then overall connection strength improves for size constraints, but seal interference becomes insufficient and sealability deteriorates
Solution Approach 1:
The patent resolves this contradiction by establishing the inequality PICCSA+BICCSA > BCCSA (box critical cross-sectional area). This quantitative parameter relationship ensures that the sum of the intermediate critical cross-sectional areas of pin and box exceeds the box critical cross-sectional area, guaranteeing sufficient seal interference and sealability while respecting size constraints for deep well applications.
Data Source
AI summary
A two-step threaded connection for steel pipe includes an intermediate seal and intermediate shoulders. A pin 2 has an inner male-threaded section 23 and an outer male-threaded section 26. A box 3 has an inner female-threaded section 33 and an outer female-threaded section 36. The pin 2 has a pin intermediate critical cross section PICCS located near an end of the first male-threaded section 23. The box 3 has a box critical cross section BCCS located near an end of the inner female-threaded section 33 and a box intermediate critical cross section BICCS located near an end of the outer female-threaded section 36. The pin 2 and the box 3 satisfy the following relationships:PICCSA+BICCSA>BCCSA, and0.70≤PICCSA/BICCSA≤0.95.