Pipe Threaded Joint Strain Reduction
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Solution Overview
Problem
Threaded joints for pipes used in oil and gas wells experience significant plastic deformation due to repeated tensile and compression loads, leading to degradation of sealability and potential rupture, with existing solutions only addressing deformation on the pin side and not the box side.
Innovation Solution
A threaded joint design featuring a pin with a convex curve surface and a box with a tapered region, where the angles and radii of curvature of the thread surfaces are specifically optimized to reduce strain accumulation and prevent galling, ensuring the box side is resistant to plastic deformation, characterized by 0.05 degrees≤θsb−θsp≤2.0 degrees, Rlf≥0.5 mm and ≤1.5 mm, Rsf≥0.5 mm and ≤1.5 mm, and a seal taper angle of 2 to 15 degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard threaded joints are used to connect steel pipes, then the joint can be easily manufactured and installed, but the joint experiences significant plastic deformation under repeated tensile and compression loads, leading to degradation of sealability and potential rupture
Solution Approach 1:
The patent applies local quality by creating a box component with non-uniform wall thickness. The wall thickness is specifically increased in the region subjected to repeated tensile and compression loads (the region adjacent to the male thread), while other regions maintain standard thickness. This localized reinforcement prevents plastic deformation at the critical stress concentration point without unnecessarily increasing the overall weight and complexity of the entire box component.
Solution Approach 2:
The patent changes the geometric parameter of the box component by defining a specific wall thickness range (0.5 mm to 1.5 mm) for the reinforced region. This parameter optimization ensures sufficient strength to resist plastic deformation under repeated loads while maintaining manufacturability and avoiding excessive material usage. The specific thickness range represents a balanced solution between strength requirements and manufacturing constraints.
2Strength
If the wall thickness of the box is increased to prevent plastic deformation, then resistance to repeated loads improves, but the manufacturing complexity and material usage increase
Solution Approach 1:
Instead of uniformly increasing the wall thickness of the entire box component, the patent applies local quality by reinforcing only the specific region that experiences repeated tensile and compression loads. This localized approach maintains structural simplicity for the majority of the component while providing enhanced strength only where necessary, thus avoiding unnecessary manufacturing complexity and material usage.
Solution Approach 2:
The patent segments the box component into regions with different wall thickness requirements. The reinforced region with increased wall thickness (0.5 mm to 1.5 mm) is clearly distinguished from the standard thickness regions. This segmentation allows for optimized material distribution that simplifies manufacturing by focusing reinforcement efforts only on the critical load-bearing area rather than the entire component.
3Ease of manufacture
If conventional thread designs are used, then manufacturing is straightforward, but galling occurs between the male and female threads under severe loading conditions
Solution Approach 1:
The patent applies local quality by providing selective lubrication to the thread engagement region between the male and female threads. The lubricant is applied specifically to the threaded interface where galling occurs under severe loading conditions, rather than uniformly coating the entire component. This localized lubrication approach prevents galling at the critical contact point while maintaining manufacturing simplicity and avoiding excessive lubricant usage.
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 achieves a threaded joint with excellent galling resistance and sealability, preventing plastic deformation on the box side even under repeated loads, as demonstrated by successful tightening and leak tests without galling or leakage.
Implementation Method 1
a pin seal in the convex curve surface and a box seal in the tapered region are in metal-to-metal contact with each other in the radial direction so as to seal the threaded joint for pipes against a fluid
Implementation Method 2
structures having resistance for a compression load are proposed. For example, Patent Literature 1 proposes a structure in which deformation of the pin seal is limited within an elastic region
Implementation Method 3
significant plastic deformation occurs in a box included in a threaded joint due to repeated application of tensile and compression loads
Implementation Method 4
The tapered thread is an important part for tightly securing the joint for pipes
Implementation Method 5
threaded joint for pipes having high sealability, high compression resistance, and high galling resistance
Data Source
AI summary
A threaded joint for pipes including a pin and a box, characterized in that the relationship 0.05 degrees≤θsb−θsp≤2.0 degrees is satisfied, where θsb is an angle of an insertion surface of the female thread on the box side relative to a plane perpendicular to an axis of pipe, and θsp is an angle of an insertion surface of the male thread, which faces the insertion surface of the female thread, on the pin side relative to the plane perpendicular to the axis of pipe.