Oilfield Pipe Threaded Joint With Dual Toroidal Metal Seals
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Solution Overview
Problem
Existing Premium threaded joints for oil and gas wells face challenges in maintaining tightness and reliability under various combined loads, including bending, compressive, and cyclic loads, due to low compression strength and external pressure resistance, which leads to potential depressurization and loss of tightness.
Innovation Solution
The design incorporates two axially spaced toroidal surfaces forming ball-and-taper seals with specific radii and tension relationships, ensuring that the circumferential stresses in the male member's end section are within the yield strength of the material, and the make-up torque is optimized to prevent plastic deformation, maintaining contact pressure across a wide range of loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the end section (shoulder) is increased to improve compression strength, then the compression strength increases, but the pipe end diameter must be reduced (run-in) which complicates manufacturing
Solution Approach 1:
The end section is divided into multiple functional zones: a first end section with a first thickness containing the metal-to-metal seal, and a second end section with a second thickness greater than the first thickness. This segmentation allows the thicker portion to provide compression strength while the thinner portion maintains manufacturability and proper seal geometry.
Solution Approach 2:
The thickness of the end section is varied locally along the axial direction. The region containing the seal maintains optimal thickness for sealing performance, while a subsequent region has increased thickness to provide compression strength. This local variation in geometry allows simultaneous optimization of sealing and compression properties without requiring overall reduction of pipe end diameter.
2Reliability
If the radial stiffness of the pin at the seal location is increased to improve resistance to external pressure, then the compression strength increases, but the design constraints on end section thickness are violated
Solution Approach 1:
Instead of increasing radial stiffness by uniformly thickening the end section (which would violate design constraints), the invention extends the thicker portion axially beyond the seal location. This axial extension provides additional compression strength without compromising the radial geometry needed for proper sealing and radial stiffness at the seal interface.
3Reliability
If the make-up torque is increased to ensure tightness under combined loads, then the tightness improves, but plastic deformation of the pin nose occurs
Solution Approach 1:
The threaded joint is pre-assembled to a predetermined angle less than the full make-up angle, establishing initial contact between sealing surfaces. This preliminary positioning ensures proper alignment and contact before final tightening, allowing the joint to achieve tightness under combined loads without requiring excessive make-up torque that would cause plastic deformation.
Solution Approach 2:
The invention changes the geometric parameters of the threaded joint, specifically the end section thickness distribution and seal geometry, to optimize the relationship between make-up torque and resulting contact pressure. This allows adequate tightness to be achieved at lower torque levels that avoid plastic deformation.
Data Source
AI summary
A threaded joint for casing pipes and production pipes has a threaded portion, and a metal-metal type sealing assembly structure in the form of a combination of sealing elements which provide 100% effective functioning of the joint under compression and tension, inter alia under the effect of internal and external fluid pressure, by observing the size ratio criteria of a ball-and-cone type seal, in which a radial sealing surface has two consecutively arranged toroidal surfaces which, in the event of axial contact between flanges, form, together with a mating sealing surface of a female member, two seals which remain tight under any combination of loads. The technical result of the group of inventions is an increase in the reliability of the threaded joint under the effect of static and variable operating loads, including external pressure, compression, twisting, and combined loads during the bending and turning of a pipe string, wherein the pipes can be used in the construction of wells having a degree of deviation of up to 13°/10 m.