Two-Step Steel Pipe Thread Connection for Seal and Tensile Balance
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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 deformation under complex loads, which compromises the connection's performance.
Innovation Solution
The threaded connection design includes specific relationships between the pin and box critical cross-sectional areas, with PICCSA + BICCSA > BCCSA and 0.70 ≤ PICCSA/BICCSA ≤ 0.95, ensuring balanced load distribution and improved sealability by optimizing the intermediate seal and shoulder surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step thread construction with intermediate shoulder surfaces and intermediate seal is used, then sealability against external pressure is improved, but critical cross sections with minimum area for bearing tensile load are created in the middle of the connection
Solution Approach 1:
The patent optimizes the geometric parameters of critical cross sections by defining specific area ratios: the pin intermediate critical cross-sectional area (PICCSA) should be 0.70-0.95 times the box intermediate critical cross-sectional area (BICCSA), and their sum should exceed the box critical cross-sectional area (BCCSA). This parameter optimization ensures both sealability and tensile load bearing capacity are maintained.
2Strength
If the area of pin intermediate critical cross section (PICCSA) is increased, then tensile load bearing capacity is improved, but the area of box intermediate critical cross section (BICCSA) decreases, affecting sealability
Solution Approach 1:
The patent establishes an optimal parameter range where PICCSA/BICCSA = 0.70-0.95, balancing the areas of both critical cross sections. This ratio ensures that neither section becomes excessively small, maintaining both tensile strength and sealability simultaneously.
3Strength
If the sum of PICCSA and BICCSA is increased, then tensile load bearing capacity is improved, but the outer diameter of the connection increases, violating size restrictions for multi-layer casing
Solution Approach 1:
The patent optimizes the distribution of critical cross-sectional areas through specific ratio constraints (PICCSA/BICCSA = 0.70-0.95 and PICCSA+BICCSA > BCCSA) that maximize tensile load bearing capacity within the given outer diameter constraints, enabling the connection to meet both strength requirements and size restrictions for multi-layer casing.
Data Source
Figure 1
Figure 2~3
AI summary
An object of the present disclosure is to ensure good sealability in a threaded connection for steel pipe of a two-step thread construction including an intermediate seal and intermediate shoulders. The pin 2 includes an intermediate seal section 22, an inner male-threaded section 23, an intermediate shoulder 24, an intermediate seal section 25 and an outer male-threaded section 26. The box 3 includes an intermediate seal section 32, an inner female-threaded section 33, an intermediate shoulder 34, an intermediate seal section 35 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 section23. The box 3 has a box critical cross section BCCS located near an end of the first female-threaded section 33 and a box intermediate critical cross section BICCS located near an end of the second female-threaded section 36. The pin 2 and the box 3 satisfy the following relationships: PICCSA+BICCSA>BCCSA, and 0.70≤PICCSA/BICCSA≤0.95.