Curved Sealing Surfaces for Pipe Joint Galling
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Solution Overview
Problem
Existing pipe joints in the oil and gas drilling industry face issues with galling due to bending forces, particularly when pipes are bent at 90° angles, leading to suboptimal sealing performance under high temperatures and pressures.
Innovation Solution
A pipe joint design featuring inclined screw threads with complementary stop shoulders and curved sealing surfaces that allow for movement under stress, maintaining a seal even when the longitudinal axes of the pin and box sections are not perfectly aligned, utilizing radii that engage each other to accommodate misalignment and distribute torque effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pipe joint is designed with rigid sealing surfaces, then the sealing performance is improved under normal conditions, but the joint becomes susceptible to galling when subjected to bending forces
Solution Approach 1:
The patent applies curvature by providing a radius on the pin stop-shoulder and a complementary radius in the box stop-shoulder recess. These curved surfaces allow the joint to accommodate bending forces and misalignment without creating stress concentrations that would lead to galling, while still maintaining effective sealing contact.
Solution Approach 2:
The curved sealing surfaces enable dynamic adaptation of the joint under load. When bending forces are applied, the radii allow the sealing surfaces to maintain contact while distributing stresses, preventing the rigid failure mode that leads to galling in traditional flat-seal designs.
2Reliability
If the pipe joint is designed to accommodate bending forces, then the joint reliability under stress is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The curved radii on the stop-shoulders provide a tolerance buffer that accommodates variations in thread alignment and pipe straightness. The gradual curvature allows misaligned threads to self-center during assembly, reducing the precision requirements compared to rigid flat surfaces while maintaining joint stability under bending loads.
3Ease of manufacture
If the sealing surfaces are made flat and rigid, then the manufacturing process is simplified, but the joint cannot withstand high bending forces without galling
Solution Approach 1:
The curved radii on the sealing surfaces are formed using standard machining operations (facing and radius tooling), which are routine manufacturing processes. This approach maintains ease of manufacture while the curved geometry provides the mechanical advantage needed to withstand bending forces, eliminating galling issues associated with flat rigid surfaces.
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 provides a stable seal capable of withstanding tensile and compressive forces, including bending, and maintains integrity at elevated temperatures, reducing the likelihood of galling and improving the joint's performance in deep, high-pressure environments.
Implementation Method 1
the curved sealing surfaces being so shaped each to lie on the arc of the circumference of a separate circle... enabling movement of the seal along the curved surface to take place when stresses are applied to the joint
Implementation Method 2
the stop shoulder on the pin including a torque shoulder, frictionally engaging a corresponding shoulder in the complementary stop shoulder
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a screw-threaded pipe joint comprising a pin (20) having at one end a male screw-threaded portion and a box (10) having at one end a female portion having a complementary screw-thread. The pin and box inter-engage along the threaded portions with the male thread extending to a male stop shoulder adjacent a complementary stop shoulder on the other portion. The complementary stop shoulder comprises a recess in the form of a cone receiver having a radial surface (23) adjacent a corresponding radial surface (15) on the complementary stop shoulder. A curved sealing surface (24) on the pin (20) sealingly engages a corresponding curved sealing surface (16) on the complementary stop shoulder of the box (10), each curved sealing surface (16, 24) lying on the arc of the circumference of a separate circle, and wherein the curvature of the box sealing surface (16) is greater than on the sealing surface (24) on the pin (20).