4-Round Pipe Thread Geometry for Composite Machining and Sealing
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Solution Overview
Problem
Existing piping thread forms, such as 8-round threads, are prone to cross-threading during installation and cannot be effectively machined into composite pipes due to issues like chipping and cracking, limiting their implementation in high-pressure and tensile load applications.
Innovation Solution
A 4-round thread form with specific angle configurations (load flank and stab flank angles) that reduces cross-threading and allows machining in composite pipes, featuring a load flank angle between 15 and 25 degrees and a stab flank angle between 60 and 62 degrees, along with a 0.0191 m (¾") taper per 0.3028 m (foot), enabling robust connections in both large and small diameter piping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If 8-round thread form is used, then high pressure and tensile load capacity is achieved, but cross-threading occurs during installation
Solution Approach 1:
The patent changes the fundamental parameters of the thread form from 8 threads per inch to 4 threads per inch, with modified flank angles (load flank angle between 15-25 degrees and stab flank angle between 60-62 degrees). This parameter change reduces the likelihood of cross-threading during installation while maintaining the structural integrity needed for high tensile load capacity and pressure resistance.
2Strength
If premium thread forms with sharp angles are used, then superior hydraulic sealing and tensile capacity are achieved, but chipping and cracking occur during machining into composite pipes
Solution Approach 1:
The patent modifies the thread geometry parameters to eliminate sharp angles that cause stress concentration. The load flank angle is set between 15-25 degrees and the stab flank angle between 60-62 degrees, creating more gradual transitions that prevent chipping and cracking during machining of composite pipes, while still achieving superior tensile capacity and hydraulic sealing.
3Strength
If buttress thread with sharp angles is used, then high strength is achieved, but chipping and cracking occur during machining
Solution Approach 1:
The patent changes the angular parameters of the thread flanks to eliminate the sharp angles characteristic of traditional buttress threads. By setting the load flank angle between 15-25 degrees and stab flank angle between 60-62 degrees, the design maintains high strength while enabling successful machining into composite materials without chipping or cracking.
Data Source
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AI summary
An apparatus is disclosed that forms a piping thread form of four threads per inch pipe (TPI). The thread form is configured to have a load flank, a load flank angle, a stab flank, a stab flank angle, a crest, and a root. Hydrostatic pressure tests using the 4-round thread form at pressures of 4,500 psi and greater resulted in failures due to thread leaks. Tensile tests using the 4-round thread form at loads of 187,400 lbs. and greater resulted in shearing at forces of 3,535 psi and greater.