Steel Pipe Threaded Seal Geometry to Prevent Galling

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Solution Overview

Problem

Existing threaded connections for steel pipes face challenges in achieving good internal and external pressure sealability while preventing galling during make-up, with current designs either compromising on sealability or galling resistance.

Innovation Solution

The threaded connection design features a pin with a tapered seal surface and a curvature surface, and a box with a corresponding taper and curvature surface, where the pin lip deforms to shift the contact point from the taper to the curvature surface after make-up, maintaining low contact pressure during assembly and high pressure post-assembly, along with a specific wall thickness ratio to enhance sealability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a metal seal with seal interference is used to achieve good sealability, then internal-pressure sealability and external-pressure sealability are improved, but contact pressure during make-up increases causing galling

Engineering Contradiction:

ImprovesealabilityVSAvoidgalling

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The seal surface is segmented into two distinct zones: a taper zone for initial contact during make-up and a curvature zone for final sealing contact. This segmentation allows different functional requirements to be met in different zones, reducing galling during assembly while maintaining sealability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The taper seal surface performs preliminary contact during the make-up process, distributing contact pressure over a larger area to prevent galling. The curvature seal surface then engages after make-up to provide the primary sealing function under operating conditions.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the pin sealing surface diameter is made larger than the box sealing surface diameter to create seal interference, then elastic recovery forces improve sealability, but contact pressure during assembly increases

Engineering Contradiction:

Improveinternal-pressure sealabilityVSAvoidcontact pressure

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

Different geometric properties are applied to different regions of the seal surface. The taper zone has a gradual slope that reduces contact pressure during make-up, while the curvature zone at the tip provides the necessary interference fit for sealability under operating conditions.

Inventive Principle:

Principle #3Local quality

3Productivity

If conventional threaded connections are used with equal inner and outer diameters, then efficiency in developing deep oil wells is improved, but sealability under pressure is compromised

Engineering Contradiction:

Improveefficiency in developing oil wellsVSAvoidsealability against pressure fluid

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A curvature surface is introduced at the tip of the pin seal, creating a spherical or rounded contact zone. This curvature provides stable and uniform contact with the box seal surface, improving sealability while maintaining the compact diameter required for deep well efficiency.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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

This design effectively reduces galling risk during assembly and improves both internal and external pressure sealability by maintaining high contact pressure post-assembly, ensuring stable and uniform seal contact along the circumference.

Implementation Method 1

the pin lip deforms to shift the contact point from the taper to the curvature surface after make-up, maintaining low contact pressure during assembly and high pressure post-assembly

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

the amount of seal interference causes the diameter of the pin sealing surface to decrease and the diameter of the box sealing surface to increase and each of the sealing surfaces tries to recover their original diameters and thus produces elastic recovery forces, which produce contact pressures on the sealing surfaces to achieve tight contact along the entire circumference

Methodology Applied

Scientific EffectElastic recovery: Elasticity

Data Source

PatentUS11624460B2Threaded connection for steel pipe

Publication Date: 2023.04.11 NIPPON STEEL CORPORATION

AI summary

A threaded connection with good internal-pressure and external-pressure sealability while preventing galling is provided. A threaded connection 1 includes a pin 10 and a box 20. The pin 10 includes a pin lip 11, a pin metal seal 13, and a cylindrical inner machined surface 14. The pin metal seal 13 includes a pin seal taper surface 16 and a pin seal curvature surface 17. The box 20 includes a box metal seal 22 parallel to the pin seal taper surface 16. The pin metal seal 13 sealingly contacts the box metal seal 22 at a seal point SP. The threaded connection satisfies the following expressions, (1) and (2),L>Lm>Ls (1), andtb/tp>1.6 (2).L is the length of the pin lip 11; Lm is the distance between the tip AP of the pin and the end point of the cylindrical inner machined surface 14; Ls is the distance between the tip AP of the pin 10 and the seal point SP; tb is the wall thickness of the box 20 as measured at the seal point SP when the connection is made up; and tp is the wall thickness of the pin 10 as measured at the seal point SP.