Semi-Flush Threaded Connection With Parallel Thread Seal Support
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Solution Overview
Problem
Existing threaded connections for oil country tubular goods in deep wells face challenges in maintaining high sealing performance under repeated loads due to lost thread sections, which lead to increased deformation and reduced sealing efficiency.
Innovation Solution
A semi-flush-type threaded connection design featuring a pin with a pin inner sealing surface, pin outer sealing surface, inner male thread, outer male thread, and pin shoulder surface, along with a box having corresponding sealing surfaces, where the inner male thread includes a parallel portion and a tapered portion with specific diameter differences to minimize gaps and deformation under pressure loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If lost thread sections are provided at the ends of the threaded connection adjacent to the seals, then the threaded connection can be made up properly with the seals positioned correctly, but the sealing performance decreases due to increased deformation and gaps
Solution Approach 1:
The patent applies local quality by providing different thread configurations in different sections of the threaded connection. The parallel portion is provided only in the inner male thread adjacent to the inner seal, while the outer male thread and other sections maintain tapered threads. This localized modification allows the make-up process to proceed correctly while minimizing deformation and maintaining sealing performance in the critical sealing area.
2Shape
If the outer diameter of the box is made about 110% of the pin outer diameter to minimize gaps in multi-stage string design, then the connection becomes semi-flush-type suitable for deep wells, but the sealing performance becomes difficult to maintain under strict dimension constrictions
Solution Approach 1:
The patent maintains the semi-flush-type connection shape with the box outer diameter at about 110% of the pin outer diameter, but locally modifies the inner male thread by providing a parallel portion adjacent to the inner seal. This local modification allows the sealing surfaces to maintain proper contact and sealing performance despite the constrained dimensions of the semi-flush design.
Data Source
AI summary
A threaded connection that provides high sealing performance is provided. A threaded connection (10) includes a pin (1) and a box (2). An inner male thread (13) of the pin (1) includes a parallel portion (131). The parallel portion (131) is located at an end portion of the inner male thread (13) adjacent to the pin inner sealing surface (11), and has thread roots parallel to the pipe axis. An inner female thread (23) of the box (2) includes a tapered portion (231). The thread height in the tapered portion (231) is larger than that in the parallel portion (131). Da<Db is satisfied, where Da is the difference in diameter between adjacent thread crests (231a) in the tapered portion (231) in a longitudinal cross section of the pin (1) and box (2) as found when the connection is not made up, and Db is the difference between the diameter of the thread root (131a) in the parallel portion (13) and the maximum diameter of the pin inner sealing surface (11).