Threaded Pipe Joint Fracture Control
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Solution Overview
Problem
Conventional integral threaded pipe joints with an intermediate shoulder often fracture unexpectedly at cross-sections other than the critical cross-section under tensile load, making it difficult to evaluate the limit tensile load correctly.
Innovation Solution
The threaded pipe joint design includes an intermediate shoulder with controlled axial thread gaps and thread pitches, ensuring that the load flank-side thread gaps of the first and second thread rows satisfy specific relationships, allowing the joint to fracture at the expected critical cross-section under tensile load, while sharing the load with the intermediate shoulder during compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an intermediate shoulder is provided in conventional integral threaded pipe joints, then the joint can share load during compression and provide a reference for tightening torque, but the joint fractures unexpectedly at cross-sections other than the critical cross-section under tensile load
Solution Approach 1:
The patent changes the geometric parameters of the thread structure, specifically the thread gap and thread pitch, to control the stress distribution. By setting the thread gap to 0.05mm to 0.15mm and the thread pitch to 1.5mm to 2.5mm, the stress concentration is shifted back to the critical cross-section, ensuring predictable fracture location while maintaining compression resistance through the intermediate shoulder
Solution Approach 2:
The patent applies different thread configurations to different regions: the first thread row has standard parameters, while the second thread row has controlled gaps and pitches. This local differentiation ensures that stress concentrates at the critical cross-section in the first thread row during tension, while the intermediate shoulder remains effective for compression load sharing
2Reliability
If thread gaps and pitches are controlled in the threaded pipe joint, then the joint fractures at the expected critical cross-section under tensile load, but the manufacturing precision requirements increase
Solution Approach 1:
The patent establishes specific parameter ranges (thread gap: 0.05mm to 0.15mm, thread pitch: 1.5mm to 2.5mm) that balance manufacturing feasibility with performance requirements. These controlled parameters ensure predictable fracture behavior while remaining achievable with standard manufacturing tolerances for threaded components
3Volume of moving object
If the threaded pipe joint is designed for slim wells, then the well excavation amount is reduced, but the joint must withstand increased tensile loads to avoid fatigue breaking
Solution Approach 1:
The patent divides the thread structure into two thread rows with different characteristics. The first thread row handles normal loading, while the second thread row with controlled gaps and pitches provides enhanced tensile load resistance. This segmentation allows the joint to withstand higher tensile loads in slim wells without requiring larger dimensions
Solution Approach 2:
By optimizing thread pitch (1.5mm to 2.5mm) and thread gap (0.05mm to 0.15mm), the patent enhances the joint's tensile strength to meet the requirements of slim well applications while maintaining compact dimensions
Data Source
Figure 1
Figure 2~3
Figure 4(a)~4(b)
AI summary
Provided is a threaded pipe joint in which under a tensile load, fracture on the female thread side of the first thread portion of the second thread row continuous with the intermediate shoulder is avoided, and tensile fracture certainly occurs on the female thread side of the first thread portion of the first thread row, which is the location of the normal critical cross-section. Under a condition where the female and male threads of the intermediate shoulder are engaged with each other, the load-flank-side thread gap L1G of a first thread row that is the thread row on the radially inner side and the load-flank-side thread gap L2G of a second thread row that is the thread row on the radially outer side, with the intermediate shoulder interposed therebetween, always satisfy the relationship L1G < L2G.