Arcuate Thread Profile for Oilfield Tubular Torsion and Sealing
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Solution Overview
Problem
Threaded connections in oilfield tubulars often fail due to stress concentrations during makeup and working, particularly in areas of elevated torsion, due to insufficient torsional strength, bearing strength, and shear strength.
Innovation Solution
A threaded pipe connection design featuring a thread profile with a crest, root, and transition surface comprising multiple arcuate surfaces and a straight-line portion, which reduces friction forces and mitigates hydraulic lock by minimizing contact area between opposing stab flanks and allowing lubricant flow, thereby enhancing torsional strength and sealing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional threaded connections are used, then structural connection is achieved, but stress concentrations occur during makeup and working leading to connection failure
Solution Approach 1:
The patent modifies the thread geometry parameters by introducing a curved stab flank profile with specific radius of curvature (R1 at crest, R2 at root) instead of traditional straight or simple filleted profiles. This parameter change redistributes the stress along the thread engagement, reducing stress concentrations at critical locations while maintaining connection reliability
Solution Approach 2:
The patent applies curvature to the stab flank surface by defining it as a curved surface with specific radii (R1 at the crest and R2 at the root) rather than a straight or planar surface. This curvature distributes contact stresses more evenly during makeup and working operations, preventing stress concentration-induced failures and improving both torsional strength and connection reliability
2Reliability
If interference fit is used, then structural and sealing connections are provided, but stress concentrations occur at thread roots and crests
Solution Approach 1:
The patent changes the geometric parameters of the thread profile, specifically the stab flank curvature radii (R1 and R2), to optimize the distribution of contact stresses. This parameter optimization reduces peak stresses at the thread roots and crests while maintaining the interference fit sealing capability, thereby improving reliability without exacerbating stress concentration
Solution Approach 2:
The curved stab flank surface with defined radii (R1 at crest, R2 at root) replaces traditional sharp or linear transitions. This curvature creates a more gradual stress distribution through the thread engagement, reducing stress concentrations at critical locations while preserving the interference fit sealing mechanism
3Strength
If traditional thread profiles are used, then connection strength is achieved, but friction forces are high during makeup causing hydraulic lock
Solution Approach 1:
The curved stab flank surface with specific radii (R1 and R2) reduces the contact area between mating threads during makeup operations compared to traditional flat or sharp-profiled threads. This reduced contact area decreases friction forces and prevents hydraulic lock while maintaining connection strength through optimized stress distribution
Solution Approach 2:
The patent applies different curvature radii at different locations: R1 at the crest and R2 at the root of the stab flank. This localized variation in geometry optimizes the balance between friction reduction during makeup (at the crest) and stress distribution during working (at the root), maintaining connection strength while reducing harmful friction forces
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design significantly improves torsional strength and reduces the likelihood of failure under stress concentrations, while also mitigating hydraulic lock issues during connection makeup, leading to more reliable and durable threaded connections in oilfield applications.
Implementation Method 1
reduces friction forces and mitigates hydraulic lock by minimizing contact area between opposing stab flanks
Implementation Method 2
A variety of thread designs, forms, and profiles have been suggested and introduced to change the distribution of torque stresses along the threaded connections of oilfield tubing
Implementation Method 3
mitigates hydraulic lock by minimizing contact area between opposing stab flanks and allowing lubricant flow
Data Source
AI summary
A threaded pipe connection includes a first tubular member having a pin end defining external threads, a second tubular member having a box end defining internal threads threadably engageable with the external threads of the pin end, and a thread profile that defines at least a portion of one of the internal or external threads and includes a crest, a root, and a transition surface extending between the crest and the root. The transition surface includes a first arcuate surface extending from a top of the crest at a first radius, a second arcuate surface extending from the first arcuate surface at a second radius, and a third arcuate surface extending from the second arcuate surface at a third radius. The first radius and the third radius are each smaller than the second radius.