Pipe Threaded Connection Geometry to Reduce Seal Galling

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Solution Overview

Problem

Existing threaded connections in the oil and natural gas industry face issues with galling due to large stand-off distances between seal surfaces, which compromise the seal and are difficult to manufacture with high precision.

Innovation Solution

A threaded connection design featuring a pin with a circumferential concave outer pin surface and a continuous extension from the pin seal surface to the pin torque shoulder, which contacts a radially inwardly extending box seal surface, allowing for maximum contact stress away from the pin end with reduced stand-off, thereby minimizing galling and simplifying manufacturing and assembly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large stand-off distance is used between pin and box torque shoulders, then the seal surfaces have more space to deform and create interference fit, but the amount of turning required to eliminate stand-off increases, causing galling of the seal surfaces

Engineering Contradiction:

Improveseal qualityVSAvoidgalling of seal surfaces

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the geometric parameters of the pin end, specifically creating a concave surface with a controlled radius of curvature. This modifies the stand-off distance profile and the deformation characteristics during make-up, allowing the seal surfaces to achieve interference fit with reduced total turning, thereby preventing galling while maintaining seal quality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies a concave spherical surface (with specified radius of curvature) to the pin end instead of a flat or sharp surface. This curvature allows progressive contact and deformation of the seal surfaces during make-up, distributing the interference fit creation over a more favorable angular range, thus reducing galling risk while achieving reliable sealing

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Object-affected harmful factors

If the seal surface is positioned close to the end of the pin, then the stand-off distance is reduced minimizing galling, but the maximum contact stress moves too close to the pin end which can compromise sealing effectiveness

Engineering Contradiction:

Improvegalling of seal surfacesVSAvoidsealing performance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent optimizes the radius of curvature parameter of the concave pin surface to position the maximum contact stress at an optimal location during make-up. This parameter adjustment ensures that the seal surface is close enough to prevent galling but far enough to maintain effective sealing pressure distribution, resolving the contradiction between preventing galling and ensuring sealing performance

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If distinct separate surfaces are provided for sealing and torque application, then precise control of sealing and torque is achieved, but manufacturing complexity increases due to the need for high precision surface distinctions

Engineering Contradiction:

Improveseal and torque control precisionVSAvoidmanufacturing precision requirements

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent merges the sealing surface and torque application surfaces into a single integrated concave surface geometry. This unified surface performs both sealing and torque transmission functions, eliminating the need for multiple precisely distinguished surfaces, thereby simplifying manufacturing while maintaining control over sealing and torque characteristics through geometric parameter optimization

Inventive Principle:

Principle #5Merging (Combining)

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 an effective seal with reduced galling risk and simplified manufacturing, maintaining excellent sealing performance while minimizing the need for precise surface distinctions.

Implementation Method 1

this additional turning from the hand tight to the shoulder tight positions causing an interference fit between the pin and box seals

Methodology Applied

Scientific EffectInterference fit: Friction

Implementation Method 2

which other bearing surfaces radially interfere and are under metal-metal contact pressure to constitute metal-metal sealing surfaces

Methodology Applied

Scientific EffectMetal-metal contact pressure: Pressure Increase

Data Source

PatentUS11614184B2Method for making a threaded connection for pipes, such as oil and gas pipes

Publication Date: 2023.03.28 ARCELORMITTAL TUBULAR PROD LUXEMBOURG SA

AI summary

A threaded connection includes a first tube having a pin, the pin having pin threads, a circumferential concave outer pin surface, and a pin torque shoulder at a free end, the concave outer pin surface including a pin seal surface and a continuous extension from the pin seal surface to the pin torque shoulder. A second tube has a box, the box has box threads for interacting with the pin threads, a circumferential inner box surface and a box torque shoulder. The inner box surface has a radially inwardly extending box seal surface, the pin seal surface contacts the box seal surface to define a seal. The seal is spaced from the free end when the pin and box torque shoulders contact, the continuous extension continuing from the seal to the pin torque shoulder. A method for making-up a threaded connection is also provided.