Two-Step Pipe Thread Geometry to Prevent Seal Shoulder Contact
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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 in high-pressure environments like oil wells.
Innovation Solution
A threaded connection design with a pin and box configuration where the pin inner sealing surface is positioned further towards the tip and the box intermediate shoulder is aligned to prevent contact, ensuring the pin inner sealing surface does not hit the box intermediate shoulder during assembly, using specific geometric relationships and sealing surface angles to maintain seal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
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 the connection can be positioned within limited pipe-wall thickness while maintaining sealability, but the pin inner sealing surface may hit the box intermediate shoulder during stabbing and alignment, potentially damaging the internal-pressure seal
Solution Approach 1:
The patent applies dimensional change by modifying the axial positioning relationship between sealing surfaces and intermediate shoulders. Specifically, the pin inner sealing surface is positioned axially further toward the pin tip, and the box intermediate shoulder is positioned axially further toward the box open end, creating sufficient axial clearance to prevent contact during stabbing and alignment operations while maintaining the flush-type or semi-flush-type connection geometry
Solution Approach 2:
The patent introduces geometric clearance as an intermediary space between the pin inner sealing surface and box intermediate shoulder. This clearance acts as a buffer zone that prevents direct contact between these surfaces during assembly, thereby protecting the seal integrity while allowing the connection to maintain its compact dimensions
2Reliability
If the pin inner sealing surface is positioned closer to the pin tip to ensure proper sealing contact, then internal pressure sealing is improved, but the sealing surface becomes more susceptible to damage from contact with the box intermediate shoulder during assembly
Solution Approach 1:
The patent applies preliminary anti-action by pre-positioning the pin inner sealing surface and box intermediate shoulder at axial locations that prevent contact before assembly occurs. The pin inner sealing surface is positioned further toward the pin tip, and the box intermediate shoulder is positioned further toward the box open end, creating protective clearance that prevents damage before it can occur during stabbing and alignment
Solution Approach 2:
The patent implements preliminary action by designing the axial positions of sealing surfaces and intermediate shoulders in advance to ensure both proper sealing contact and protective clearance. The geometric relationships are predetermined during design, with the pin inner sealing surface positioned to contact the box inner sealing surface for sealing while maintaining clearance from the box intermediate shoulder
Data Source
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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 hB<hP+LB−LP×tanθseal LSP<LB−LP