Threaded Pipe Joint Sealing Geometry for Combined Load Tightness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing threaded joints in the oil and gas industry face challenges in maintaining tightness under combined loads, cyclic operations, and repeated assembly/disassembly, leading to potential leakage and damage, especially under multidirectional loads and corrosive conditions.
Innovation Solution
A threaded pipe joint design featuring a toroidal-conical surface on the nipple tip and a mating conical-toroidal surface on the coupling, with optimized sealing surface geometry and radial interference, ensuring even contact pressure distribution and stability under combined loads, and enhanced radial stiffness to prevent seizing and maintain tightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded joints are used, then assembly and disassembly is straightforward, but tightness cannot be maintained under combined loads and cyclic operations
Solution Approach 1:
The sealing function is segmented into two independent units: radial seal and end-face seal. Each seal operates independently to address different loading conditions, with the radial seal handling axial loads and the end-face seal handling multidirectional loads, thereby maintaining tightness without requiring a single complex sealing structure
Solution Approach 2:
The sealing approach transitions from single-point contact to two-dimensional area contact. The end-face seal introduces a new sealing dimension perpendicular to the radial seal, creating a comprehensive sealing system that covers both radial and axial directions, effectively preventing leakage under combined loads
2Reliability
If sealing surfaces are increased to improve tightness, then leakage resistance improves, but contact pressure distribution becomes uneven leading to metal scuffing
Solution Approach 1:
Different sealing surfaces are assigned different functions and pressure characteristics. The radial seal operates under high contact pressure for axial loading, while the end-face seal operates under distributed pressure for multidirectional loading. This local differentiation allows each seal to optimize its pressure distribution, preventing metal scuffing while maintaining leakage resistance
Solution Approach 2:
The end-face sealing surfaces utilize curved (toroidal-conical and conical-toroidal) geometries that naturally distribute contact pressure more evenly across the sealing interface. This curvature prevents stress concentration at specific points, reducing the risk of metal scuffing while maintaining effective sealing under varied loading conditions
3Reliability
If radial interference is increased to improve seal tightness, then tightness margin improves, but radial stiffness increases causing seizing
Solution Approach 1:
The sealing function is divided between radial and end-face seals, allowing the radial seal to use moderate interference (50-80% of plastic compression) while the end-face seal provides additional tightness through area contact. This segmentation reduces the need for high radial interference, preventing seizing during screwing operations
Solution Approach 2:
The toroidal-conical and conical-toroidal surfaces with optimized radii (R1 = 0.05-0.15D, R2 = 0.03-0.1D) create a gradual pressure build-up during assembly. This curved geometry distributes the interference effect over a larger area and longer contact path, reducing peak contact stresses that would otherwise cause seizing while maintaining adequate tightness margin
4Productivity
If thread taper ratio is increased to improve assembly speed, then screwing speed improves, but tightness under external pressure deteriorates
Solution Approach 1:
The sealing function is separated into radial and end-face components, with the end-face seal specifically designed to handle external pressure conditions. This allows the thread geometry to be optimized for assembly speed (taper ratio 1:10 to 1:20) without compromising tightness under pressure, as the end-face seal compensates for any pressure-related sealing deficiencies
Solution Approach 2:
The seal radii parameters (R1 and R2) are specifically optimized to work with the chosen thread taper ratio. The relationship between R1, R2, and the thread geometry creates a balanced system where moderate taper ratios can be used for both fast assembly and adequate pressure resistance, as the seal geometry compensates for reduced mechanical advantage
Data Source
Figure 1a~1c
Figure 2a~3b
Figure 4~5
AI summary
The invention relates to a threaded pipe joint comprising internal and external mating members with conical surfaces, on which threaded portions having the general surface profile of a frusto-conical shape are formed, wherein radial sealing surfaces forming a radial sealing unit and end-face sealing surfaces forming an end-face sealing unit are provided on the internal and external mating members from the side of the smaller diameter of the frustrum, wherein the internal mating member has at least one threadless portion, on which the radial sealing surface is located, characterized in that the threadless portion of the internal mating member, on which the radial sealing surface is located, is configured with enhanced thickness such that the generatrix of the radial sealing surface is located higher than the thread root line by a value of δ in range from 0,60 to 0,9 mm, and the number of full-crest turns on the internal mating member engaged with the counter-turns of the external member is 6-10 turns.