Tapered Root Thread Form for Tubular Connections
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing threaded connections for tubular flow conduits face challenges in withstanding high torque and bending loads, while also requiring efficient assembly and minimizing material usage, with a need for improved tensile strength and faster make-up characteristics.
Innovation Solution
The development of a thread form with varying thread height and geometry, featuring cylindrical crests and tapered roots, and optionally multi-start threads, which maximizes the 'real-estate' area for enhanced tensile strength and torque resistance, allowing for quick and secure coupling of tubular sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional uniform thread forms are used, then manufacturing is simpler, but tensile strength and torque resistance are insufficient
Solution Approach 1:
The thread form transitions from uniform to non-uniform geometry, with varying pitch and depth along the thread length. The root radius varies from a first value at the major diameter to a second value at the minor diameter, creating localized stress distribution optimization that enhances tensile strength without requiring complete geometric redesign of the entire thread structure.
Solution Approach 2:
The patent modifies critical thread parameters including pitch (distance between threads), depth (height of thread engagement), and root radius along the thread length. These parameter variations create a gradient structure that optimizes stress distribution, with finer pitch and greater depth at critical stress zones to improve tensile strength and torque resistance.
2Strength
If more thread material is used to increase strength, then torque resistance improves, but material cost and manufacturing time increase
Solution Approach 1:
The thread form concentrates material where most needed - with increased pitch and depth at the root zone where stress concentration occurs during torque loading. The varying root radius creates a stress-relief geometry that maximizes torque resistance while minimizing unnecessary material in less critical zones, optimizing the strength-to-material-ratio.
3Strength
If thread depth is increased for better engagement, then connection strength improves, but assembly time increases
Solution Approach 1:
The pitch varies along the thread length, with closer spacing (greater engagement) at the root zone where connection strength is most critical, and wider spacing toward the tip where full engagement is less demanding. This gradient pitch structure achieves optimal connection strength while reducing the total number of threads required, thereby decreasing assembly time.
4Strength
If uniform thread pitch is used, then manufacturing is easier, but stress distribution is suboptimal
Solution Approach 1:
The varying pitch and depth are concentrated in specific zones (particularly at the root with varying root radius) rather than uniformly distributed. This localized geometric variation optimizes stress distribution at critical stress concentration points while maintaining simpler geometry in less critical zones, balancing manufacturing ease with stress optimization.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A thread form is shown which is used to make a threaded connection between two tubular members and which is capable of being screwed together and subsequently unscrewed. A pin member is provided having external threads with stab flanks and load flanks and flat crests and roots for mating with the mating internal threads of a box member to make up a pipe connection. The thread crests on the pin member are cylindrical with respect to a central longitudinal axis of the tubular member while the thread roots are cut on a taper so that the height of the threads vary over the length of the thread form. The threads on the pin and box members can also be cut oppositely so that respective members of the thread forms are mirror images of each other.