Threaded Pipe Connector Buttress Thread Design
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Solution Overview
Problem
Existing threaded pipe connectors in the petroleum and natural gas industry face issues with pull-out failure, sealing reliability, and processing difficulties, particularly when designing for high-grade steel and large calibers, due to inadequate thread design and high precision requirements.
Innovation Solution
A threaded pipe connector featuring a modified API buttress thread with a specific thread height to pitch ratio, combined cylindrical and conical sealing areas, and circular arc transitions to reduce stress concentration and facilitate mass production, ensuring reliable sealing and improved connection strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If API buttress thread is used for big caliber, thick-wall, high grade steel threaded sleeves, then connection strength is improved, but pull-out failure occurs due to inadequate thread design
Solution Approach 1:
The patent modifies the API buttress thread parameters by optimizing the ratio of thread height to pitch to 0.25-0.35, adjusting the bearing surface angle t2 to -15-3°, and setting the guide surface angle t1 to 10-50°. These parameter changes enhance the thread's load-bearing capacity and prevent pull-out failure while maintaining connection strength.
2Reliability
If sealing interference and sealing length are increased to ensure high performance sealing, then sealing reliability is improved, but processing precision requirements increase and galling tendency increases
Solution Approach 1:
The patent divides the sealing function into two separate sealing faces in a multistage seal configuration. The first sealing face provides primary sealing with moderate interference, while the second sealing face provides backup sealing. This segmentation allows each sealing face to operate under less stringent precision requirements while maintaining overall high sealing reliability.
3Reliability
If multistage sealing is used to reduce drawbacks of single stage sealing, then sealing reliability is improved, but two sealing faces are not separated in conventional configuration making it no difference in performance and sacrificing reliability
Solution Approach 1:
The patent separates the two sealing faces in the multistage seal configuration along the axial dimension, positioning them at different locations along the thread engagement. This spatial separation in another dimension allows each sealing face to function independently and effectively, truly realizing the benefits of multistage sealing rather than having overlapping or coincident sealing surfaces.
4Reliability
If sealing surfaces are separated in multistage shoulder with double torque shoulder, then sealing reliability is improved, but processing is very difficult and yield is pretty low
Solution Approach 1:
The patent combines the multistage seal configuration with a single torque shoulder design, integrating the functions of sealing and torque transmission into a unified structure. This merging eliminates the need for complex double torque shoulder configurations while maintaining separated sealing surfaces, thereby improving manufacturability and yield without sacrificing sealing reliability.
Data Source
AI summary
A threaded pipe connector, including: a pipe body including an external thread on one end; and a coupling including an internal thread on a corresponding end. Both the external thread and the internal thread are buttress threads capable of matching with each other. A ratio of thread height to pitch is 0.25-0.35, bearing surface angle is −15-3°, and guide surface angle is 10-50°. A clearance is provided between a thread crest and a thread root after engagement of the external and internal threads. A sealing area between the pipe body and the coupling includes in sequence a first cylindrical transitional area, a cylindrical sealing area, a secondary cylindrical transitional area, a conical sealing area, and a conical transitional area. Tapers of both sides of the conical sealing area are the same. One end of the conical transitional area is connected with a torque shoulder.