Casing Thread Connection Geometry to Prevent Jamming and Galling
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Solution Overview
Problem
Existing thread connections for oil, gas, and gas-condensate well casings fail to maintain tightness, particularly gas tightness, under multidirectional combined mechanical loads, and suffer from jamming and damage to sealing surfaces during assembly and operation.
Innovation Solution
The thread connection features male and female elements with tapered trapezoidal threads and an internal sealing unit, including additional surfaces between sealing and shoulder end face surfaces, designed with specific angles and radii to prevent jamming and damage, ensuring high tightness and resistance to mechanical loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional tapered trapezoidal threads with parallel crests and roots are used, then the connection can be assembled, but jamming occurs at the initial stage of make-up and sealing surfaces get damaged under mechanical loads
Solution Approach 1:
The thread turn profile is segmented into distinct zones: a first portion with a first slope angle (15-20°) for easy make-up alignment, and a second portion with a second slope angle (5-10°) for load-bearing and sealing. This segmentation allows the connection to progress through make-up stages without jamming while maintaining reliability under load.
Solution Approach 2:
Different portions of the thread turn profile are given different geometric properties - the first portion has a steeper slope for alignment and ease of engagement, while the second portion has a gentler slope for maintaining tightness under mechanical loads. This local differentiation resolves the contradiction between ease of operation and reliability.
2Reliability
If sealing surfaces are made to contact directly, then tightness is achieved, but the surfaces suffer from damage (galling) during operation under high mechanical loads
Solution Approach 1:
The thread connection geometry is designed to distribute mechanical loads progressively through the thread engagement, cushioning the impact on sealing surfaces before full contact is achieved. The progressive slope angles prevent sudden load application that would cause galling, while still ensuring tightness is achieved through proper sealing surface contact.
3Strength
If the thread connection is designed for high load bearing, then mechanical strength is improved, but the make-up process becomes more complex and prone to jamming
Solution Approach 1:
The thread profile parameters are optimized with specific slope angles (first portion: 15-20°, second portion: 5-10°) that balance load bearing capacity with ease of make-up. These parameter changes allow the connection to handle high mechanical loads while maintaining a relatively simple geometric form that is not prone to jamming during assembly.
Data Source
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AI summary
The invention refers to oil and gas equipment and can be applied for thread connection for casings used for construction of vertical, directional and horizontal wells. The connection consists of a male and female elements, the ends of which, both externally and internally, are produced correspondingly with tapered trapezoidal threads, sealing, transition and shoulder end surfaces. The crests and roots of thread turn profile are parallel to axial line of thread. The additional surfaces are produced in the form of taper surface on the female element and of taper surface or convex spherical surface on the male element. Transition from sealing surfaces to additional surfaces are produced in the form of concave spherical surface on the male element and of convex spherical surface on the female element. High tightness of the connection under sufficient mechanical loads is achieved by means of improved characteristics of the connection make-up, prevention of jamming of the connection at the initial stage of make-up, lack of damages (galling) of sealing surfaces.