Steel Pipe Threaded Joint With Incomplete Thread Seal Geometry
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Solution Overview
Problem
Conventional threaded joints for steel pipes in harsh environments, such as deep-underground or ultra-deep water oil wells, fail to maintain adequate sealing performance against both internal and external pressures due to insufficient consideration of contact pressure changes caused by these pressures.
Innovation Solution
A threaded joint design featuring a female threaded portion with an incomplete thread section and a complete thread section, where the incomplete thread section has a length at least three times the thread pitch, and a flank angle of less than 0 degrees, allowing for radially outward expansion under internal pressure while maintaining stiffness and preventing radial contraction under external pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If clearances are provided between roots of male threaded portion and crests of female threaded portion to relieve mating contact, then contact pressure between seal surfaces is amplified under internal pressure, but thread mating stability deteriorates
Solution Approach 1:
The threaded portion is divided into two segments with different clearance characteristics. The first threaded portion has clearances between roots and crests to allow radial expansion and amplify seal contact pressure under internal pressure. The second threaded portion has normal clearance to maintain thread mating stability and prevent excessive movement.
Solution Approach 2:
Clearance characteristics are localized to specific regions. Near the seal surface, larger clearances are provided to relieve mating contact and allow pressure amplification. Farther from the seal surface, normal clearances are maintained to ensure stable thread engagement and prevent galling.
2Reliability
If the flank angle is increased to allow radial expansion under internal pressure, then sealing performance against internal pressure is improved, but resistance to radial contraction under external pressure deteriorates
Solution Approach 1:
The threaded portion is segmented into two regions with different flank angle characteristics. The first threaded portion has a larger flank angle that facilitates radial expansion under internal pressure, improving seal contact. The second threaded portion has a normal flank angle that provides structural resistance to radial contraction under external pressure.
Solution Approach 2:
Flank angle is optimized locally for different functional requirements. Near the seal surface, a larger flank angle allows greater radial flexibility for seal enhancement. Farther from the seal surface, a standard flank angle maintains structural integrity and resistance to external pressure effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design enhances sealing performance against internal pressure while maintaining sealing integrity against external pressure, reducing the likelihood of galling and ensuring stable thread mating, thus improving the joint's overall performance in harsh environments.
Implementation Method 1
When internal pressure is applied, the region near the seal surface in the threaded portion of the pin is expanded radially outward from the inside to cause enlargement of the diameter, whereby the contact pressure between the seal surfaces is amplified
Data Source
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AI summary
The load flanks (15) in the male threaded portion (11) of the pin (10) and the load flanks (24) in the female threaded portion (21) of the box (20) have a flank angle θ of less than 0 degrees. The female threaded portion (21) is divided into, in order from near the seal surface (26), an incomplete thread section (21b) and a complete thread section (21 a). In the female threaded portion (21), over the entire area including the two thread sections (21a, 21b), roots (23) collectively define a single tapered periphery. The incomplete thread section (21b) has a length of at least three times the thread pitch and has a thread height lower than a thread height of the complete thread section (21a). In a made-up state, the shoulder surfaces (17, 27) are in contact with each other, the seal surfaces (16, 26) are in contact with each other, and in the incomplete thread section (21b), clearances are provided between the roots (13) of the male threaded portion (11) and the crests (22) of the female threaded portion (21). Consequently, sealing performance against external pressure is maintained and sealing performance against internal pressure is improved.