OCTG Threaded Joint Seal Geometry for High-Compression Sealability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing premium threaded joints for oil country tubular goods face challenges in ensuring consistent sealability due to insufficient contact at the seal portion during fitting engagement, particularly under varying environmental conditions and stresses.
Innovation Solution
The design involves setting a difference in radius of curvature between the arc of the annular outer peripheral surface portion of the pin and the arc of the annular inner peripheral surface portion of the box within a ±10% range, and ensuring a center position difference in the pipe axial direction of 2 mm or less, forming a projecting arc on the pin and a recessed arc on the box to enhance contact length and sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the seal portion surfaces are divided into three arcs with substantially the same radius of curvature, then stress concentration is decreased, but sufficient contact state at the seal portion during fitting engagement is not always ensured
Solution Approach 1:
The invention changes the geometric parameters of the seal portion by forming a projecting arc on the pin side and a recessed arc on the box side, with specific radius of curvature relationships (Rp1 < Rp2 and Rb1 > Rb2). This parameter modification ensures both adequate contact during engagement and reduced stress concentration, resolving the contradiction between sealability and stress resistance.
Solution Approach 2:
The invention introduces asymmetry in the arc configurations of the seal portion. The pin side has a projecting arc with smaller radius of curvature, while the box side has a recessed arc with larger radius of curvature. This asymmetric design creates optimal contact conditions during fitting engagement while maintaining stress distribution, thereby improving both sealability and stress concentration resistance.
2Strength
If the radius of curvature of seal portion arcs are set substantially equal, then stress concentration is reduced, but contact length at the seal portion is insufficient
Solution Approach 1:
The invention modifies the radius of curvature parameters differently for the pin side and box side arcs. Specifically, Rp1 < Rp2 and Rb1 > Rb2, creating a parameter relationship that simultaneously increases contact length and maintains stress distribution. The projecting arc on the pin and recessed arc on the box work together to achieve both objectives.
Solution Approach 2:
The invention utilizes curved arc surfaces with specifically designed radius of curvature relationships. The projecting arc and recessed arc configurations create extended contact length through optimized curvature, while the specific radius relationships ensure proper stress distribution across the seal portion.
3Ease of manufacture
If standard threaded joint design is used, then manufacturing simplicity is maintained, but sealability under severe environmental conditions is insufficient
Solution Approach 1:
The invention modifies specific geometric parameters of the seal portion (arc radii and their relationships) while maintaining the overall threaded joint structure. This selective parameter change improves sealability under compression and severe environmental conditions without significantly complicating the manufacturing process, as the modifications are localized to the seal portion geometry.
Data Source
AI summary
A threaded joint includes: a pin having an annular outer peripheral surface portion formed on a tip end side of a steel pipe, and an externally-threaded portion formed from the annular outer peripheral surface portion toward a center of a steel pipe in an axial direction of the steel pipe; and a box having a cavity in which the pin is housed, wherein an internally-threaded portion which threadedly engages with the externally-threaded portion and an annular inner peripheral surface portion which is brought into contact with and abuts against the annular outer peripheral surface portion are formed in the cavity, wherein the pin and the box are joined to each other due to threaded engagement between the externally-threaded portion and the internally-threaded portion.