Modified API Buttress Coupling Hoop Stress Reduction

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Solution Overview

Problem

Standard API Buttress Connections fail due to excessive mechanical stress in deviated wells, leading to plastic yielding and splitting, which increases well costs and poses environmental risks in shale formations.

Innovation Solution

A modified API Buttress Coupling with an internal mechanical stop and altered thread geometry, including increased pitch diameter and reduced thread interference, to control plastic deformation and hoop stress, while maintaining gas tightness and compatibility with standard API Pins.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If standard API Buttress Connection is used, then cost of tubulars is reduced, but resistance to mechanical failure under high stress decreases

Engineering Contradiction:

Improvecost of tubularsVSAvoidresistance to mechanical failure

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The coupling geometry parameters are modified by increasing the pitch diameter and adjusting the thread profile. This changes the stress distribution characteristics, allowing the coupling to withstand combined loads (make-up torque, internal pressure, bending, and torsional loads) without exceeding yield strength, while still using standard API Buttress Connection components

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The thread interference region is optimized by increasing pitch diameter, which concentrates the load-bearing capability in the critical threaded connection zone. This local geometric modification enhances the overall connection strength without requiring changes to the entire tubular system

Inventive Principle:

Principle #3Local quality

2Device complexity

If standard API Buttress Connection is used, then simplicity of connection design is maintained, but plastic yielding and splitting occur under combined loads

Engineering Contradiction:

Improvesimplicity of connection designVSAvoidyield strength under combined loads

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The pitch diameter parameter is increased and the thread profile is adjusted to modify stress distribution. This geometric parameter change allows the coupling to resist plastic yielding and splitting under combined loads while maintaining the standard API Buttress Connection design framework

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The coupling is pre-designed with optimized geometry parameters before installation. The increased pitch diameter and modified thread profile are built into the coupling structure in advance, so that when installed with standard API Pins, the connection automatically possesses enhanced strength characteristics without requiring additional components or complex assembly procedures

Inventive Principle:

Principle #10Preliminary action

3Stress or pressure

If increased pitch diameter is implemented, then hoop stress is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvehoop stressVSAvoidthread geometry precision

Core Design Contradiction:

Stress or pressureVSManufacturing precision

Solution Approach 1:

The pitch diameter is increased to reduce hoop stress concentrations in the coupling wall. While this does require precise manufacturing to maintain thread compatibility, the standardization of the modified coupling dimensions allows for controlled precision requirements that are achievable with conventional manufacturing processes

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10107423B1Coupling for connecting threaded tubulars

Publication Date: 2018.10.23 TEJAS TUBULAR PROD

AI summary

A casing coupling has a taper which is different from the taper of a standard API Pin. The coupling has a thread pitch diameter which is increased relative to that of a standard API coupling but which still mates with a standard API pin.