Corrosion Protection for Earth Boring Bit Legs
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Solution Overview
Problem
Earth boring bits, particularly their steel legs, are prone to breakage due to corrosion, especially in areas around the welds, leading to leg fracture during drilling operations, especially in geographic regions with corrosive drilling fluids.
Innovation Solution
A protective anti-corrosive coating comprising alloys like nickel, chromium, copper, aluminum, or silicon is applied to the outer surfaces of the bit legs, including areas above and below the ball plug weld, to inhibit corrosion and reduce the likelihood of leg breakage. The coating can be a nickel-based alloy or a polymer, applied through methods such as high-velocity oxygen fuel (HVOF) spraying or thermal spraying, and may cover both hardfaced and tungsten carbide compact surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hardfacing and tungsten carbide compacts are applied to the bit leg outer surface, then wear resistance is improved, but corrosion protection is reduced and leg breakage occurs
Solution Approach 1:
The bit leg outer surface is divided into different functional zones: hardfacing and tungsten carbide compacts provide wear resistance in high-wear areas, while anti-corrosive coating provides corrosion protection in areas susceptible to corrosion. This segmentation allows each material to perform its optimal function without compromising the other.
Solution Approach 2:
The invention uses a composite structure combining hardfacing (carbide particles in iron/nickel/cobalt matrix), tungsten carbide compacts, and anti-corrosive coating (nickel-based alloy or polymer). This composite material approach allows simultaneous achievement of wear resistance and corrosion protection that neither material could provide alone.
2Reliability
If anti-corrosive coating is applied to the entire outer surface including weld areas, then corrosion protection is improved, but manufacturing complexity increases
Solution Approach 1:
The anti-corrosive coating is selectively applied to specific areas of the bit leg outer surface where corrosion is most likely to occur, such as around the ball plug weld and in other high-stress regions. This localized application provides effective corrosion protection while minimizing the complexity of the coating process compared to full-surface coating.
3Strength
If the bit leg is made of steel for strength, then structural strength is improved, but susceptibility to corrosion increases
Solution Approach 1:
The anti-corrosive coating acts as an intermediary layer between the steel bit leg and the corrosive drilling fluid environment. This intermediate protective layer prevents direct contact between the corrosive environment and the steel, thereby protecting the steel structure from corrosion while maintaining its structural strength.
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 anti-corrosive coating effectively reduces the risk of leg breakage by protecting high-stress areas from corrosive drilling fluids, extending the lifespan of the bit legs and preventing premature failure.
Implementation Method 1
An anti-corrosive coating is formed on an outer surface of the leg to reduce the tendency for leg breakage
Implementation Method 2
The coating can be a nickel-based alloy or a polymer, applied through methods such as high-velocity oxygen fuel (HVOF) spraying or thermal spraying
Implementation Method 3
The coating can be a nickel-based alloy or a polymer, applied through methods such as high-velocity oxygen fuel (HVOF) spraying or thermal spraying
Data Source
AI summary
An earth boring bit has a steel body having at least one leg with a depending bearing pin. A cone having cutting elements is rotatably mounted to the bearing pin. A ball plug weld is on the outer surface of the leg. A layer of hardfacing applied to part of the outer surface of the leg, the hardfacing having carbide particles in a matrix. A corrosion resistant coating containing at least 50% nickel is formed on parts of the outer surface of the leg that are free of the layer of hardfacing both above and below the ball plug weld.