Oil Well Pipe Threaded Joint Galling Resistance
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Solution Overview
Problem
Conventional threaded joints for oil country tubular goods face challenges in achieving excellent galling resistance, particularly at the pin pipe end side, due to high contact reaction forces, which are difficult to industrially adjust and control.
Innovation Solution
The solution involves setting the ratio of chamfer length to thread pitch for the pin thread between 1.0 and 3.0, which reduces the contact reaction force by creating an incomplete thread portion that disperses the force and lowers stiffness, thereby preventing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the contact reaction force at the pin pipe end side is increased to ensure firm connection, then the connection strength is improved, but galling is more likely to occur
Solution Approach 1:
The invention changes the geometric parameters of the threaded portion by introducing a chamfered surface at the pin pipe end. Specifically, the chamfer length L is set to satisfy 0.05 inch ≤ L ≤ 0.15 inch, which modifies the contact area and force distribution. This parameter change allows the contact reaction force to be dispersed over a larger area, reducing the contact stress and preventing galling while maintaining adequate connection strength.
Solution Approach 2:
The invention introduces a new dimensional element (the chamfered surface) at the pin pipe end, transforming the original point/line contact into a面 contact. The chamfered surface extends the contact zone along the axial direction, creating a gradual transition zone that distributes the contact reaction force over multiple thread ridges rather than concentrating it at a single location, thereby preventing galling.
2Object-affected harmful factors
If the thread gap is adjusted to decrease contact reaction force and prevent galling, then galling resistance is improved, but the adjustment is difficult to implement industrially
Solution Approach 1:
Instead of adjusting the thread gap (which requires precise control of pitch and is difficult to implement industrially), the invention changes to a different parameter - the chamfer length L. This parameter can be easily controlled during the threading process using standard machining operations, making it suitable for industrial production while achieving the same goal of reducing contact reaction force and preventing galling.
3Reliability
If a radial-directional seal method is used to reduce dependence on lubrication conditions, then seal reliability is improved, but the contact reaction force distribution remains unfavorable for galling prevention
Solution Approach 1:
The invention applies local quality modification by introducing a chamfered surface specifically at the pin pipe end region where galling is most likely to occur. This local structural modification creates a favorable stress distribution zone that reduces contact reaction force concentration, while the rest of the threaded joint maintains its radial-directional seal characteristics for reliable sealing performance.
Data Source
Figure 1~2
Figure 3A~3C
AI summary
The prior art has a drawback that it is difficult to provide a threaded joint for an oil country tubular goods having excellent galling resistance at a threaded portion on a pin pipe end side as industrial products. Provided is a threaded joint for an oil country tubular goods having excellent galling resistance, which is a premium joint, a ratio L/p of a chamfer length of pin thread L to a thread pitch p being set to 1.0 or more to 3.0 or less.