Threaded Joint Pitch Variation for Load Flank Galling
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Solution Overview
Problem
Conventional threaded joints for oil country tubular goods experience galling due to concentrated loads on the load flank face of the pin pipe end side, which cannot be effectively reduced by existing solutions.
Innovation Solution
The threaded joint design incorporates a pitch change in the internally-threaded portion, where the pitch is reduced by half of the entire length from the thread end to the box center side, gradually decreasing the thread gap and dispersing the contact force, thereby reducing the concentrated load on the load flank face.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional threaded joint design is used, then the joint can be manufactured with standard thread pitch, but concentrated load occurs on the load flank face causing galling
Solution Approach 1:
The patent applies local quality by varying the thread pitch along the length of the threaded portion. The first region has a first pitch while the second region has a second pitch that is different from the first pitch. This local variation in thread geometry distributes the contact force differently along the load flank face, preventing concentrated load and galling while maintaining manufacturability through controlled pitch variation.
2Reliability
If the thread pitch is changed to distribute load, then galling resistance improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the thread pitch parameter along the axial direction of the threaded portion. The pitch transitions from a first value in the first region to a second value in the second region. This controlled parameter variation optimizes load distribution and prevents galling while remaining compatible with standard threading processes, balancing improved reliability with acceptable manufacturing complexity.
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3
AI summary
In the prior art, only the case where the contact is made on the stabbing flank face 31B is estimated and hence, the prior art has a drawback that when a highly concentrated load acts on the load flank face 30P of the threaded portion on the pin pipe end side, the concentrated load cannot be decreased. In a premium joint, a pitch change is made such that an internally-thread pitch 20B has the same value as an externally-thread pitch 20P from a thread end portion on a box 1 end side to a pitch change position (PCP) taken on a box center side with respect to a position away from the thread end portion by 1/2 of an entire length of the threaded portion, and the internally-thread pitch is changed to a value less than the externally-thread pitch at the pitch change position (PCP) so that a thread gap 10 is gradually decreased from the pitch change position to a position (PCP) of the thread end portion on the box center side, and the thread gap is eventually set to a value which is 0.2 to 0.8 times as large as the thread gap 10 before the pitch change is made.