Oil drilling tools play a vital role in the process of oil exploration and exploitation. However, due to long-term operation in harsh working environments, such as high temperature, high pressure, corrosive media, and friction and impact with rocks, oil drilling tools are prone to wear, corrosion and cracks, which seriously affect their service life and working performance. Laser cladding technology, as an advanced surface engineering technology, provides an effective solution for the repair and strengthening of oil drilling tools.

1. Common forms of damage to oil drilling tools

(I) Wear
During the drilling process, oil drilling tools rub against rocks, mud, etc., especially the drill pipe joints, drill bits and other parts, which are prone to wear. Long-term wear will lead to a reduction in the size and strength of the drilling tools, affecting drilling efficiency and safety.

(II) Corrosion
There are various corrosive media in the underground environment, such as hydrogen sulfide, carbon dioxide, brine, etc. These media will corrode the surface of the drilling tools, causing pitting and pitting on the surface of the drilling tools, reducing the bearing capacity and service life of the drilling tools.

(III) Cracks
During the operation, the drilling tools are subjected to alternating loads, impact loads and thermal stresses, etc., and cracks are easily generated on the surface or inside. The expansion of cracks will cause the drilling tools to break, causing serious safety accidents and economic losses.

2. Principles and characteristics of laser cladding technology

Laser cladding technology uses a high-energy-density laser beam to irradiate the surface of the substrate, so that the preset or synchronously fed cladding material is quickly melted and forms a good metallurgical bond with the substrate surface, thereby forming a cladding layer with specific properties on the substrate surface.

Laser cladding technology has the following characteristics:

(i) The cladding layer is metallurgically bonded to the substrate, with high bonding strength and not easy to fall off.

(ii) The heat input is small, and the heat-affected zone on the substrate is small, which can effectively reduce the deformation and changes in the organizational properties of the substrate.

(iii) The dilution rate of the cladding layer is low, and the composition and properties of the cladding layer can be precisely controlled.

(iv) It can achieve local repair and strengthening, with strong pertinence, and can save materials and costs.

(v) It can produce high-performance cladding layers such as wear-resistant, corrosion-resistant, and high-temperature-resistant to meet the needs of different working conditions.

3. Application of laser cladding technology in the repair and strengthening of oil drilling tools

(I) Repair and strengthening of drill pipe joints
Drill pipe joints are the connecting parts between drill pipes. They are subjected to large torque and tensile and compressive loads during drilling, and are prone to wear and fatigue cracks. Using laser cladding technology, a layer of wear-resistant and fatigue-resistant alloy materials, such as cobalt-based alloys and nickel-based alloys, are clad on the surface of the drill pipe joints, which can significantly improve the surface hardness, wear resistance and fatigue strength of the drill pipe joints and extend their service life.

(II) Repair and strengthening of drill bits
During the drilling process, the drill bit is in direct contact with the rock and is severely worn. By cladding a layer of wear-resistant and high-temperature resistant alloy materials, such as tungsten carbide and ceramics, on the surface of the drill bit through laser cladding technology, the wear resistance and cutting performance of the drill bit can be improved, the service life of the drill bit can be extended, and the drilling efficiency can be improved.

(III) Repair and strengthening of drill collars
During the drilling process, the drill collars play a role in increasing drilling pressure and stabilizing the drilling tools, and are susceptible to wear and corrosion. Using laser cladding technology to clad a layer of corrosion-resistant and wear-resistant alloy materials, such as stainless steel and nickel-based alloys, on the surface of the drill collar can improve the corrosion resistance and wear resistance of the drill collar and ensure the safe and reliable operation of the drill collar.

4. Selection of laser cladding process parameters

When repairing and strengthening oil drilling tools with laser cladding, the reasonable selection of process parameters is the key to ensuring the quality of cladding. The main process parameters include laser power, scanning speed, powder feeding speed, spot diameter, overlap rate, etc.

(I) Laser power

The size of the laser power directly affects the melting depth and dilution rate of the cladding layer. Generally speaking, the greater the laser power, the greater the melting depth of the cladding layer and the higher the dilution rate. When repairing oil drilling tools, the appropriate laser power should be selected according to the material, size and degree of damage of the drilling tools to ensure a good combination of the cladding layer and the substrate, while avoiding excessive dilution.

(II) Scanning speed

The scanning speed determines the action time and heat input of the laser beam on the substrate surface. If the scanning speed is too fast, the bonding strength between the cladding layer and the substrate is insufficient; if the scanning speed is too slow, the heat input is too large, which can easily lead to deformation of the substrate and cracking of the cladding layer. Therefore, it is necessary to select a suitable scanning speed based on factors such as laser power and the characteristics of the cladding material.

(III) Powder feeding speed
The powder feeding speed affects the composition and thickness of the cladding layer. If the powder feeding speed is too fast, the number of unmelted particles in the cladding layer will increase, affecting the quality of the cladding layer; if the powder feeding speed is too slow, the thickness of the cladding layer will be insufficient. The powder feeding speed should be reasonably adjusted according to parameters such as laser power and scanning speed to obtain a cladding layer with excellent performance.

(IV) Spot diameter
The size of the spot diameter determines the energy distribution of the laser beam and the width of the cladding layer. Generally speaking, the larger the spot diameter, the more uniform the energy distribution, but the lower the precision of the cladding layer; the smaller the spot diameter, the more concentrated the energy, the higher the precision of the cladding layer, but it is prone to local overheating and deformation. When repairing oil drilling tools, the appropriate spot diameter should be selected according to the damaged part and size of the drilling tools.

(V) Overlap rate
The overlap rate refers to the degree of overlap between adjacent cladding paths. If the overlap rate is too small, the surface of the cladding layer will be uneven and grooves will appear; if the overlap rate is too large, the cladding layer will be uneven in structure and the performance will be reduced. Usually, the overlap rate should be controlled between 30% and 50%.

5. Performance test after repair and strengthening

In order to ensure the quality of oil drilling tools after laser cladding repair and strengthening, it is necessary to perform performance testing on the repaired drilling tools. The main inspection items include appearance inspection, size inspection, hardness test, metallographic structure analysis, bonding strength test, wear resistance test, corrosion resistance test, etc.

(I) Appearance inspection
Observe the surface quality of the cladding layer through visual inspection or with the help of tools such as magnifying glasses to check whether there are defects such as cracks, pores, slag inclusions, etc.

(II) Size inspection
Use measuring tools to measure the size of the repaired drilling tools to check whether they meet the design requirements.

(III) Hardness test
The hardness of the cladding layer is tested with a hardness tester to understand the hardness distribution of the cladding layer and ensure that it meets the use requirements.

(IV) Metallographic structure analysis
The metallographic structure of the cladding layer and the substrate is observed through a metallographic microscope to check the bonding between the cladding layer and the substrate, as well as the organizational morphology and defects inside the cladding layer.

(V) Bonding strength test
The bonding strength between the cladding layer and the substrate is tested using methods such as tensile test and shear test to ensure that the bonding strength meets the requirements of relevant standards.

(VI) Wear resistance test
The wear resistance of the cladding layer is tested using a friction and wear tester, and compared with the unrepaired drill bit to evaluate the wear resistance of the repaired drill bit.

(VII) Corrosion resistance test
The repaired drill bit is placed in a simulated underground corrosion environment for a corrosion test to test its corrosion resistance and determine whether it can meet the requirements of the underground working environment.

As an advanced surface repair and strengthening technology, laser cladding technology has significant advantages in the repair and strengthening of oil drilling tools. By rationally selecting cladding materials, optimizing process parameters, and conducting strict performance testing, damaged oil drilling tools can be effectively repaired and strengthened, their service life and working performance can be improved, the cost of oil exploration and production can be reduced, and strong support can be provided for the development of the oil industry. With the continuous development and improvement of laser cladding technology, its application prospects in the field of oil drilling tools will be broader.