Large-Diameter Steel Pipe Wedge Threads for Shear-Resistant Sealing
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Solution Overview
Problem
High-torque threaded connections for large-diameter steel pipes experience shear fractures due to inadequate shear resistance in the male threadform, leading to concentrated loads and subsequent fractures in subsequent threads, compromising torque resistance and sealability.
Innovation Solution
The design incorporates a male threadform with a taper thread having a dovetail-shaped cross section, where the stab-flank pitch is smaller than the load-flank pitch, and the thread width at the tip is optimized to ensure sufficient shear resistance, with specific expressions defining the thread dimensions to prevent shear fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional design standards are used for large-diameter steel pipes, then the threaded connection can be manufactured with standard dimensions, but shear fractures occur in the male threadform due to inadequate shear resistance
Solution Approach 1:
The patent modifies the thread geometry parameters specifically for large-diameter pipes (OD > 240 mm). The male threadform is designed with a minimum thread width Wmin ≥ 3 mm at the tip region, and the thread depth TH is optimized to satisfy specific expressions relating to pipe dimensions. These parameter changes increase the shear area and structural strength of the male threadform to prevent shear fractures under high tensile loads, while maintaining compatibility with standard manufacturing processes.
2Strength
If the thread width at the tip is increased to improve shear resistance, then shear fractures are prevented, but the torque resistance and sealability may be compromised
Solution Approach 1:
The patent applies local quality by differentiating the thread geometry along the length of the male threadform. The thread width Wmin is specifically increased at the tip region (where shear fractures occur) while maintaining appropriate thread dimensions in other regions. The stab-flank pitch is made smaller than the load-flank pitch in specific regions, creating localized structural variations that enhance shear resistance at critical locations without compromising overall torque resistance and sealability.
Solution Approach 2:
The patent optimizes multiple thread parameters simultaneously: thread width Wmin ≥ 3 mm, thread depth TH, stab-flank pitch, and load-flank pitch. These parameters are adjusted to satisfy specific mathematical expressions that balance shear resistance with torque resistance and sealability. The coordinated parameter changes ensure that increasing shear resistance does not come at the expense of other critical performance attributes.
3Strength
If the stab-flank pitch is made smaller than the load-flank pitch, then the thread structure is strengthened, but the manufacturing complexity increases
Solution Approach 1:
The patent implements local quality by applying different pitch values to different flanks of the thread structure. The stab-flank pitch is specifically reduced compared to the load-flank pitch in the tip region of the male threadform, creating a localized structural reinforcement. This selective pitch variation strengthens the thread where shear fractures are most likely to occur, while maintaining simpler geometry in other regions to minimize manufacturing complexity.
Data Source
AI summary
A threaded connection for large diameter steel pipe exhibits high torque resistance and high sealability and, at the same time, provides a shear resistance that suits the size of the steel pipe to be connected. The threaded connection includes a tubular pin provided on a tip of a steel pipe with large diameter, and a tubular box 20 adapted to be drawn up on the pin as the pin is screwed in. The pin includes a male threadform made with a taper thread. The box includes a female threadform made with a taper thread. Each of the threadforms are wedge threads and have a dovetail-shaped cross section. The male threadform is designed such that the width of the thread in an end region of the male threadform closer to the tip is set to a size corresponding to the size of the pipe body of the steel pipe.