Threaded Joints with Localized Friction Coatings
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Solution Overview
Problem
Existing threaded joints for oil and gas extraction pipes face challenges in achieving high torsional strength while maintaining low make-up torque and avoiding the drawbacks of lubricants, such as seizure, dirt entrapment, and non-uniform distribution, which limit their performance and reliability under varying environmental and operational conditions.
Innovation Solution
A threaded joint design featuring a high friction anti-seize coating on overall surfaces and a low friction coating on specific areas, particularly for radial contact, allowing for controlled torque values and enhanced torsional strength without increasing make-up torque, and providing corrosion resistance across a wide range of conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single anti-seize coating with high friction factor is used to enhance yield torque, then torsional strength is improved, but make-up torque increases and joint seizure risk increases
Solution Approach 1:
The patent applies different friction coatings to different regions of the thread surface. High friction factor coatings are applied to specific zones where they contribute most to yield torque, while low friction factor coatings are applied to other zones to reduce make-up torque and prevent seizure. This spatial differentiation of friction properties resolves the contradiction between enhancing strength and ease of operation.
2Ease of operation
If a single anti-seize coating with low friction factor is used to reduce make-up torque, then ease of operation is improved, but yield torque decreases and torsional strength is reduced
Solution Approach 1:
The patent strategically places low friction factor coatings in specific regions where they effectively reduce make-up torque without significantly compromising overall yield torque. The high friction factor coatings in other regions compensate for the reduced friction, maintaining adequate torsional strength while achieving easier make-up operation.
3Ease of operation
If dope is used as lubricant to reduce make-up torque and prevent seizure, then ease of operation is improved, but dirt entrapment and non-uniform distribution occur
Solution Approach 1:
The patent replaces the mechanical lubrication system (dope application) with a surface engineering system (coatings). The coatings are applied during manufacturing with uniform control, eliminating the manual application variability and dirt entrapment issues associated with dope. This substitution maintains ease of operation while significantly improving reliability and consistency.
4Reliability
If dope-free solutions are used to avoid lubricant drawbacks, then reliability is improved, but make-up torque reaches high values
Solution Approach 1:
The patent maintains the reliability advantage of dope-free solutions by using permanent surface coatings instead of temporary lubricants. The coatings prevent seizure and ensure consistent friction characteristics across multiple make-up operations. Simultaneously, the strategic placement of low friction factor coating regions reduces make-up torque to acceptable levels, resolving the contradiction between reliability and ease of operation.
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 solution enables higher torsional strength with lower shoulder torque and higher yield torque, reducing operator influence on friction factors and maintaining performance through multiple make-up and break-out operations, overcoming limitations of both doped and dope-free solutions.
Implementation Method 1
a first layer with high friction and anti-seize properties laid on the overall surface of the pin or box members
Implementation Method 2
a second layer with low friction proprieties laid on specific parts of the overall surfaces of either one of pin or box members
Data Source
AI summary
A threaded metallic joint has the thread surface of pin (100) and box (200) covered with a coating comprising a first layer (24) laid on the overall surface of the pin member (100), and a second layer (25) laid on part of the surfaces of either one of the pin or box members. In a first aspect, the coating comprises a first layer with high friction and anti-seize properties laid on the overall surface of the pin member (100), and a second layer (25) with low friction properties laid on specific parts of the surfaces of either one of the pin or box members. Preferably the specific surfaces are those which are in reciprocal radial contact during make-up until pin and box reach the point where shoulders (9, 10) abut. The second layer may contain polytetrafluoroethylene (PTFE). In a second aspect the first layer with a high friction and anti-seize properties laid on the overall surface of the box member (200).