Wedge Thread Coating for Tubular Joint Sealing
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Solution Overview
Problem
Wedge threads in oilfield tubular connections face challenges in achieving reliable thread seals and resisting galling due to their intricate and high-tolerance sealing characteristics, which can lead to premature failure under high pressures and increased make-up torque.
Innovation Solution
A surface coating system comprising a fluoropolymer-based coating applied to specific regions of the threads, combined with a resin coating in areas devoid of the fluoropolymer, forming a uniform layer that enhances sealability, anti-galling properties, and corrosion resistance, while reducing metal-to-metal contact and stress during make-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single coating material is applied to wedge threads, then the application process is simple, but the coating cannot simultaneously provide optimal sealing, anti-galling, and corrosion resistance properties
Solution Approach 1:
The coating system is segmented into two distinct layers: a fluoropolymer-based coating applied to specific regions (crests and substantially central regions of thread roots) providing sealing and anti-galling properties, and a resin coating applied to remaining regions providing corrosion resistance. This segmentation allows each layer to optimize its function without compromising the others.
Solution Approach 2:
Different coating materials are applied to different regions of the thread based on local functional requirements. The fluoropolymer coating is applied to regions requiring low friction and sealing (crests and central root regions), while the resin coating is applied to regions requiring corrosion resistance. This local quality approach ensures optimal performance in each specific area.
2Reliability
If high make-up torque is applied to achieve reliable sealing, then sealability improves, but galling and thread surface damage increase
Solution Approach 1:
The fluoropolymer-based coating acts as an intermediary layer between the metal thread surfaces, providing a low-friction interface that reduces direct metal-to-metal contact. This intermediary layer allows high make-up torque to be applied for reliable sealing while preventing galling and thread surface damage that would occur with direct metal contact.
Solution Approach 2:
The coating system changes the friction and surface properties of the thread interface. The fluoropolymer coating reduces the coefficient of friction, allowing controlled slippage during make-up that distributes stress evenly, while the resin coating provides corrosion resistance. This parameter change enables high torque application without galling.
3Ease of manufacture
If uniform coating thickness is applied across all thread surfaces, then application is simplified, but sealing performance in critical regions is compromised
Solution Approach 1:
The coating system applies different materials and thicknesses to different regions based on local sealing requirements. The fluoropolymer coating is applied to crests and substantially central regions of thread roots where sealing is critical, with controlled thickness to ensure proper sealing function. This local quality approach prioritizes sealing performance in critical regions over uniformity.
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 coating system significantly improves the sealing and anti-galling performance of wedge threads, extending the life of the connections by reducing galling and corrosion, and lowering maintenance and replacement costs, with test data showing no thread surface galling or seal failure under high torque conditions.
Implementation Method 1
A surface coating system comprising a fluoropolymer-based coating applied to specific regions of the threads, combined with a resin coating in areas devoid of the fluoropolymer, forming a uniform layer that enhances sealability, anti-galling properties, and corrosion resistance, while reducing metal-to-metal contact and stress during make-up.
Implementation Method 2
A surface coating system comprising a fluoropolymer-based coating applied to specific regions of the threads, combined with a resin coating in areas devoid of the fluoropolymer, forming a uniform layer that enhances sealability, anti-galling properties, and corrosion resistance
Data Source
Figure 1A~1B
Figure 2
AI summary
A threaded joint for pipes includes a pin member (101) and a box member (102), the pin member having an external thread (106) configured to correspond to an internal thread (107) of the box member, a thread form of the internal and external threads having generally dovetail - shaped profile with stab flanks (231,232)and load flanks (225,226) and flat roots and crests (222,291), wherein the internal threads are increasing in width in one direction on the box and the external threads are increasing in width in the other direction on the pin, so the roots, crests, and flanks of the threads move together and form seals (112) that resist the flow of fluids between the seals. The threaded joint further includes a fluoropolymer-based coating (310) applied to specific regions of the threads and a resin coating (312) disposed in regions of the threads that are devoid of the fluoropolymer-based coating, wherein the fluoropolymer-based coating and the resin coating are configured to form a layer of substantially uniform thickness on the overall surface of the threads.