Two-Step Pipe Thread Connection That Protects the Inner Seal
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Solution Overview
Problem
In threaded connections with a two-step thread construction, the pin inner sealing surface can hit the box intermediate shoulder during alignment, potentially damaging the internal-pressure seal, especially in environments with high internal pressures.
Innovation Solution
A threaded connection design with a pin and box configuration that includes a first and second male/female thread, a pin and box intermediate shoulder, and specific sealing surfaces, where the pin inner sealing surface is positioned to prevent contact with the box intermediate shoulder, ensuring the seal point is protected and maintaining sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step thread construction with intermediate shoulders is used to achieve flush-type or semi-flush-type threaded connections under strict size restrictions, then sealability against internal and external pressures is improved, but the pin inner sealing surface may hit the box intermediate shoulder during stabbing causing damage
Solution Approach 1:
The patent introduces a new spatial dimension parameter (axial distance relationship between seal surface and intermediate shoulder) to resolve the conflict. By controlling the axial positioning of the pin inner sealing surface relative to the box intermediate shoulder, the design ensures that the seal surface extends axially beyond the intermediate shoulder, preventing contact during stabbing while maintaining the two-step thread construction for sealability.
2Reliability
If the pin inner sealing surface is positioned to prevent contact with the box intermediate shoulder, then protection against damage is improved, but the design space for thread and seal structures becomes more constrained
Solution Approach 1:
The patent applies preliminary action by pre-positioning the pin inner sealing surface such that it extends axially beyond the box intermediate shoulder before any stabbing operation occurs. This advance positioning ensures that during the stabbing process, the seal surface cannot contact the intermediate shoulder, as the protective spatial relationship is already established in the design phase.
Data Source
AI summary
In a threaded connection for pipe with a two-step thread construction, including intermediate shoulders, during stabbing, the internal-pressure sealing surface of the pin near its tip is prevented from contacting the intermediate shoulder of the box and thus receiving damage. LP, LB, hP and hB shown in FIG. 2 satisfy Expressions (1) and (2), provided below. θseal is the angle of slope of the straight line connecting the two ends, as determined along the axial direction, of the internal-pressure sealing surface of the pin. Expression (3), provided below, is also satisfied.LP<LB (1)hB<hP(LB−LP)×tan θseal (2)LSP<LB−LP (3)