Two-Step Threaded Connection Grooves for Tensile Break Prevention

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Solution Overview

Problem

In two-step thread constructions for threaded connections in oil wells, it is challenging to ensure large cross-sectional areas for pin and box intermediate critical cross sections to enhance torque resistance and prevent breaks under tensile loads, while also simplifying the creation of intermediate shoulder surfaces.

Innovation Solution

A threaded connection design featuring a tubular pin and box with a first and second male/female thread, an intermediate shoulder surface, and circumferential grooves that facilitate easier creation and enhance contact area, reducing strain and stress concentration at critical cross sections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If intermediate shoulder surfaces are provided in two-step thread construction to improve torque resistance, then torque resistance is enhanced, but the cross-sectional areas of pin and box intermediate critical cross sections are reduced making them prone to breaks under tensile loads

Engineering Contradiction:

Improvetorque resistanceVSAvoidtensile strength at intermediate critical cross sections

Core Design Contradiction:

ForceVSStrength

Solution Approach 1:

The connection is divided into multiple functional zones: first and second thread engagement regions, intermediate shoulder surfaces for torque resistance, and circumferential grooves that segment the structure to reduce stress concentration. This segmentation allows each region to perform its specific function without compromising overall strength

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the connection are given different properties: the intermediate shoulder surfaces provide torque resistance while the circumferential grooves create localized stress relief zones. The grooves are strategically positioned to maintain large cross-sectional areas at critical locations while still allowing intermediate shoulders to function

Inventive Principle:

Principle #3Local quality

2Force

If intermediate shoulder surfaces are designed with large contact area to improve torque resistance, then torque resistance is enhanced, but the creation of intermediate shoulder surfaces becomes more difficult

Engineering Contradiction:

Improvetorque resistanceVSAvoidease of creating intermediate shoulder surfaces

Core Design Contradiction:

ForceVSEase of manufacture

Solution Approach 1:

The circumferential grooves are designed with curved surfaces that smoothly transition from the intermediate shoulder surfaces. This curvature eliminates sharp corners and makes the machining process easier while still providing the necessary stress relief and maintaining large contact areas for torque resistance

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Shape

If tight size restrictions are imposed on flush-type and semi-flush-type threaded connections to allow thread and seal structures in limited pipe-wall thickness, then size constraints are satisfied, but it becomes challenging to ensure both high strength and sealability

Engineering Contradiction:

Improvesize constraintsVSAvoidconnection strength and sealability

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

Multiple functional elements are nested within the limited pipe-wall thickness: threads are positioned concentrically, seal structures are integrated within the thread geometry, and circumferential grooves are formed as annular features. This nesting allows all required structures to coexist in the limited radial space while maintaining their individual functions

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The design utilizes the axial dimension extensively to accommodate multiple thread steps and seal structures, rather than only relying on radial thickness. By distributing structures along the axial direction and using circumferential grooves to manage stress, the design satisfies tight radial size constraints while maintaining strength and sealability

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS11828391B2Threaded connection

Publication Date: 2023.11.28 NIPPON STEEL CORPORATION

AI summary

In a threaded connection of a two-step thread construction including intermediate shoulder surfaces, a break is prevented near the intermediate critical cross sections upon application of a tensile load, and the intermediate shoulder surfaces are easier to create, thus improving productivity. The outer periphery portion of a pin located between an intermediate shoulder surface of the pin and a second male thread is provided with a circumferential groove including a curved surface smoothly contiguous to the intermediate shoulder surface, thereby mitigating plastic strains generated near the pin intermediate critical cross section PICCS. The inner periphery portion of a box located between an intermediate shoulder surface of the box and a first female thread is provided with a circumferential groove including a curved surface smoothly contiguous to the intermediate shoulder surface, thereby mitigating plastic strains generated near a box intermediate critical cross section BICCS.