Threaded Joint Shoulder Geometry for Oil Country Tubular Goods
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Solution Overview
Problem
Conventional threaded joints for oil country tubular goods face challenges in maintaining durability under compressive loads, leading to excessive plastic deformation and crevice corrosion, especially in harsh environments like oceans and polar regions, where the existing methods fail to prevent gap formation and corrosion.
Innovation Solution
A radial-seal-type threaded joint design is implemented, where the pin-side and box-side shoulder angles, seal interference quantity, and seal point distance satisfy specific relationships (θ2−θ1=α×δ/xp with α=7 to 14) and the pin distal end thickness is set to be at least 0.25 times the raw pipe thickness to prevent excessive deformation and crevice corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded joint design is used, then ease of manufacture is maintained, but durability and resistance to crevice corrosion deteriorate under compressive loads
Solution Approach 1:
The patent applies parameter changes by optimizing the shoulder angle (θ) to be within 5° to 15° and the nose radius (R) to be within 0.05D to 0.1D (where D is the outer diameter). These specific parameter ranges prevent excessive plastic deformation and gap formation at the shoulder, thereby improving durability and resistance to crevice corrosion while maintaining manufacturability within standard tolerances.
Solution Approach 2:
The patent applies local quality by specifically modifying the geometry of the nose and shoulder regions. The rounded nose with controlled radius and the optimized shoulder angle create a stress distribution that prevents localized plastic deformation and gap formation, addressing the durability issue at the critical location without requiring changes to the entire joint structure.
2Reliability
If conventional threaded joint design is used, then device complexity is kept simple, but resistance to crevice corrosion deteriorates due to gap formation
Solution Approach 1:
The patent eliminates crevice corrosion by changing the geometric parameters of the shoulder region. By optimizing the shoulder angle (θ) to 5°-15° and the nose radius (R) to 0.05D-0.1D, the design ensures that the shoulder surfaces remain in full contact under compressive loads, preventing gap formation and the subsequent crevice corrosion that would occur with conventional designs.
Solution Approach 2:
The patent introduces asymmetry in the nose geometry by rounding only the distal end with a specific radius, while maintaining the standard threaded portion geometry. This asymmetric modification at the critical nose region prevents stress concentration and gap formation without requiring symmetric changes to the entire joint, thus avoiding increased device complexity.
3Reliability
If conventional threaded joint design is used, then manufacturing cost is kept low, but durability deteriorates due to excessive plastic deformation
Solution Approach 1:
The patent improves durability by changing the geometric parameters to optimized ranges: shoulder angle θ of 5° to 15° and nose radius R of 0.05D to 0.1D. These parameter changes prevent excessive plastic deformation during make-up and service, extending the joint's service life without requiring expensive materials or complex manufacturing processes.
Solution Approach 2:
The patent applies preliminary action by pre-rounding the nose with a controlled radius before threading. This preliminary geometric modification ensures that during the make-up process, the stress is distributed evenly from the outset, preventing excessive plastic deformation and material displacement that would otherwise occur, thereby improving durability without adding significant manufacturing cost.
Data Source
AI summary
A premium threaded joint has a pin-side shoulder angle θ1, a box-side shoulder angle θ2, a seal interference quantity δ and a seal point distance xp satisfying θ2−θ1=α×δ/xp, α=7 to 14, and a pin distal end thickness tp1 defined by a difference Re−Ri between a radius Re of a pin most distal end portion and an inner radius Ri of a pin distal end portion is 0.25 times or more as large as a pin raw pipe thickness tp0.