Nitrided Grip Elements for Corrosion-Resistant Tubulars
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Solution Overview
Problem
Conventional grip surfaces for tubular workpieces, especially those made from corrosion-resistant alloys, face challenges in achieving sufficient traction while minimizing marking and preventing iron contamination, which is critical for maintaining the corrosion resistance of stainless steel tubulars.
Innovation Solution
The use of grip elements with a substrate material that is substantially free of free iron, featuring pyramidically shaped die teeth with a nitrided surface, which provides the necessary strength and hardness to grip CRA workpieces without marking and prevents iron contamination, utilizing surface-hardening treatments like nitriding, boronizing, or chromizing to ensure effective gripping without surficial iron.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional grip surfaces are used on CRA tubulars, then sufficient traction can be achieved, but iron contamination occurs and marking is caused on the tubular surface
Solution Approach 1:
The grip element applies local quality by using a CRA substrate material specifically at the grip surface where contact with the tubular occurs, while the rest of the body can be made of different material. This ensures the critical contact area has the necessary corrosion resistance and non-contaminating properties, while maintaining overall structural integrity.
Solution Approach 2:
The grip element employs composite material construction by combining CRA substrate material with appropriate hardening treatments or coatings on the gripping surfaces. This creates a multi-layered structure that provides both the corrosion resistance of CRA and the enhanced hardness needed for effective gripping without marking.
2Strength
If harder grip surfaces are used to increase durability and slip resistance, then gripping effectiveness improves, but marking and surface damage to CRA tubulars increases
Solution Approach 1:
The invention changes the material parameters by selecting CRA substrate material with specific hardness characteristics that are inherently lower than conventional steel, and controlling the hardness through heat treatment or surface treatments to achieve an optimal range that provides durability without excessive hardness that would cause marking.
Solution Approach 2:
Local quality is applied by treating only the gripping surfaces with hardening processes or coatings, while the bulk material maintains its base CRA properties. This ensures the contact surfaces have enhanced slip resistance without the entire grip element being excessively hard, which would increase marking risk.
3Ease of manufacture
If conventional steel grip elements are used, then manufacturing is easier and cost is lower, but free iron contamination occurs on CRA tubular surfaces
Solution Approach 1:
Homogeneity is applied by making the grip element substrate entirely from CRA material, ensuring that no conventional steel or iron-containing materials are present anywhere in the component that could contaminate the tubular surface. This uniform material composition eliminates the source of free iron contamination throughout the entire part.
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
This solution ensures reliable gripping of CRA tubulars with minimal marking and iron contamination, maintaining the corrosion resistance of stainless steel surfaces while providing sufficient slip resistance and durability.
Implementation Method 1
the surfaces of the toothed structures (or at least portions thereof) are strengthened and hardened by nitriding
Implementation Method 2
the product of the normal force multiplied by the effective friction coefficient of the interfacial region (i.e., the traction limit) must always be greater than the combined applied loads acting as a shear force
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A grip element for gripping a tubular CRA workpiece has a hardened grip surface carrying an array of generally pyramidic die teeth, which may have either pointed or rounded tips, with the configuration of the tooth tips being selected for effective gripping of the CRA workpiece by means of an interference grip, and without unacceptable marking the CRA workpiece. The die tooth density over the grip surface may be selected to minimize accumulation of contaminants between teeth and/or to facilitate removal of accumulated contaminants. The substrate of the grip element may comprise a stainless steel having no free iron, with the grip surface being hardened by nitriding. Optionally, the tips of the grip element may truncated after nitriding to partially expose the stainless steel substrate. In alternative embodiments, the grip element may have a carbon steel substrate with a nitrided grip surface.