The Necessity and Process Flow of Laser Cladding Repair for Oil External Pipe Equipment

I. Introduction

In the petroleum industry, external pipeline equipment, as a critical carrier for oil and gas transportation, operates long-term in complex and harsh environments. From extraction sites to refineries, and from land pipelines to subsea lines, petroleum external pipeline equipment faces various forms of damage, such as corrosion, wear, and erosion. These damages not only affect the transportation efficiency of pipelines but also pose serious threats to safety production. Traditional repair methods often suffer from issues like unstable repair quality and short post-repair equipment lifespan. Laser cladding technology, as an advanced surface engineering technique, provides an innovative solution for the repair of petroleum external pipeline equipment. It significantly enhances the performance and service life of external pipeline equipment, playing a vital role in ensuring the safety of petroleum production and reducing operational costs.

II. Common Issues in Petroleum External Pipeline Equipment and the Necessity of Laser Cladding Repair

1. Common Issues

Corrosion Issues: Petroleum often contains corrosive media such as hydrogen sulfide, carbon dioxide, and chlorides. Long-term exposure leads to chemical and electrochemical corrosion on the inner walls of external pipeline equipment. For example, in pipelines transporting sulfur-containing crude oil, hydrogen sulfide reacts with metals to form sulfide corrosion products, gradually thinning the pipeline walls and reducing their strength. Additionally, electrolytes and microorganisms in the soil can cause corrosion on the outer walls of external pipeline equipment, especially in harsh soil environments like damp or saline-alkali areas, where corrosion rates accelerate.

Wear Issues: When petroleum flows through pipelines, the solid particles it carries (such as sand grains) cause scouring wear on the inner walls of external pipelines. In areas with higher flow velocities, wear is more severe. Furthermore, at pipeline connections, elbows, and other locations, turbulent flow and fluid impact can easily cause localized wear. For instance, in gathering pipelines at oil and gas extraction sites, due to the high sand content in crude oil, the wear rate at pipeline elbows is several times higher than in straight sections.

Erosion Issues: When petroleum contains high-pressure gases or liquids, high-speed jets are generated as they pass through throttling devices, valves, and other components of external pipeline equipment, causing intense erosion on the equipment surface. This erosion can result in surface damage such as pitting and dents, and in severe cases, lead to perforation and leakage. For example, erosion is common in valves of natural gas transmission pipelines due to high gas pressure and flow velocity.

2. Necessity of Laser Cladding Repair

Extending Equipment Service Life: By applying coatings with excellent corrosion resistance, wear resistance, and erosion resistance on the surface of petroleum external pipeline equipment through laser cladding, contact between corrosive media and the substrate can be effectively blocked, reducing wear and erosion damage. This significantly extends the equipment's service life. For example, in the repair of an oil transmission pipeline at an oilfield, the use of laser cladding technology extended the pipeline's service life from the original 3-5 years to 10-15 years.

Ensuring Safety Production: Timely repair of damage to external pipeline equipment can prevent safety incidents such as fires and environmental pollution caused by pipeline leaks, ensuring the safe operation of petroleum production and reducing casualties and property losses. For example, in the repair of subsea oil transmission pipelines, laser cladding technology enables high-precision repair of pipeline defects without disrupting normal production, ensuring the safe and stable operation of subsea pipelines.

Reducing Maintenance Costs: Compared to replacing new external pipeline equipment, laser cladding repair offers advantages such as lower costs and shorter cycles. Repaired equipment can restore its original performance and continue to meet production demands, avoiding the high procurement costs and production losses associated with frequent equipment replacement. For example, laser cladding repair of crude oil transmission pipelines at a large refinery costs only 30%-50% of replacing new pipelines, with repair time reduced by over 50%.

III. Process Flow of Laser Cladding Repair for Petroleum External Pipeline Equipment

1. Surface Pretreatment

Cleaning: Methods such as chemical cleaning or high-pressure water jet cleaning are used to remove oil stains, impurities, rust, and other contaminants from the surface of external pipeline equipment, ensuring a clean cladding surface. For example, for pipelines with large diameters, high-pressure water jet cleaning vehicles can be used for internal cleaning, with cleaning pressures reaching tens of megapascals, effectively removing dirt from the inner walls.

Grinding: Grinding equipment (such as electric grinders, sandpaper, etc.) is used to polish the surface of external pipeline equipment, removing oxide scales and rough layers to improve surface flatness and provide a good foundation for subsequent cladding. For areas with localized deformation or damage, shaping and grinding are also required to restore the surface to a relatively flat state.

Nondestructive Testing: Nondestructive testing techniques (such as ultrasonic testing, magnetic particle testing, and radiographic testing) are used to conduct comprehensive inspections of the cleaned and ground external pipeline equipment to determine the location, size, and type of defects on the surface and inside the equipment. This provides a basis for developing a reasonable cladding repair plan. For example, ultrasonic testing instruments can detect crack defects up to several millimeters deep inside pipelines.

2. Cladding Material Selection

Based on the working environment, type of damage, and performance requirements of the petroleum external pipeline equipment, suitable cladding materials are selected. Common cladding materials include nickel-based alloys, cobalt-based alloys, iron-based alloys, and composite materials reinforced with phases such as tungsten carbide and ceramics.

Corrosion Resistance Applications: In highly corrosive environments, such as pipelines transporting sulfur-containing crude oil, nickel-based alloys (e.g., Inconel series) can be selected as cladding materials. Nickel-based alloys offer excellent corrosion resistance, effectively resisting erosion from corrosive media like hydrogen sulfide and carbon dioxide.

Wear Resistance Applications: For areas prone to wear, such as the inner walls of pipelines transporting sand-containing crude oil, composite materials containing tungsten carbide particles, such as nickel-based or cobalt-based composites, can be used as cladding materials. Tungsten carbide has high hardness and good wear resistance, significantly enhancing the wear resistance of the cladding layer.

Comprehensive Performance Requirements: When petroleum external pipeline equipment requires multiple performance characteristics, the cladding material composition can be optimized, or multi-layer cladding can be employed to meet the requirements. For example, a transition layer with good bonding properties (such as iron-based alloy) can be clad onto the substrate surface first, followed by a composite coating with corrosion and wear resistance (such as nickel-based tungsten carbide composite) on the transition layer.

3. Laser Cladding Operation

Equipment Debugging: Based on the size, shape, and cladding process requirements of the external pipeline equipment, the laser cladding equipment is debugged, including parameters such as laser power, spot diameter, scanning speed, powder feed rate, and powder feed angle. Ensuring stable equipment operation and accurate parameter settings is crucial for the smooth progress of the cladding process and the quality of the cladding layer.

Cladding Method Selection: Laser cladding primarily includes pre-placed and synchronous methods. The pre-placed method involves uniformly spreading the cladding material on the substrate surface in advance and then scanning it with a laser beam for melting. The synchronous method involves feeding the cladding material directly into the molten pool through a powder feed device while the laser irradiates. In the repair of petroleum external pipeline equipment, the synchronous cladding method is more widely used because it allows real-time control of the cladding material addition, ensuring uniformity and quality of the cladding layer. For example, handheld synchronous powder feed laser cladding equipment can be used for repairing small-diameter pipelines, while automated synchronous powder feed laser cladding production lines can be used for large-diameter pipelines.

Multi-Layer Cladding: For situations requiring thicker cladding layers or higher performance requirements, a multi-layer cladding process can be adopted. After each layer is clad, appropriate cooling and inspection are required to ensure good interlayer bonding and the absence of defects. When performing the next layer of cladding, laser parameters and powder feed rates need to be adjusted to ensure the quality and performance of each cladding layer. For example, in repairing subsea oil transmission pipelines, a multi-layer cladding process of 3-5 layers is typically used to enhance the pipeline's corrosion resistance and pressure resistance.

4. Post-Treatment

Heat Treatment: Appropriate heat treatment, such as annealing or tempering, is applied to the clad external pipeline equipment to eliminate residual stress within the cladding layer, improve the microstructure, and enhance the comprehensive performance of the cladding layer. The heat treatment temperature and time should be reasonably selected based on the characteristics of the cladding material and the substrate material. For example, for some nickel-based alloy cladding layers, an annealing process at 800-900°C for 1-2 hours can be used.

Surface Machining: Mechanical machining (such as turning or grinding) or surface polishing methods are used to treat the surface of the clad external pipeline equipment to meet specified dimensional accuracy and surface roughness requirements. For example, for external pipeline equipment that needs to be assembled with other components, turning machining can control the outer diameter dimensional accuracy of the clad pipeline within ±0.1mm and achieve a surface roughness of Ra0.8-1.6μm.

Quality Inspection: Nondestructive testing (such as ultrasonic testing and penetrant testing) and physicochemical performance tests (such as hardness testing, tensile testing, and corrosion resistance testing) are conducted again to perform comprehensive quality inspections on the repaired external pipeline equipment. This ensures the cladding layer is free from defects like cracks and pores and meets performance requirements. For example, hardness testing at different positions on the cladding layer surface using a hardness tester requires hardness values to deviate within specified limits to ensure uniformity of cladding layer quality.

IV. Conclusion

Laser cladding technology, with its unique technical advantages, demonstrates significant application potential in the field of petroleum external pipeline equipment repair. Through in-depth analysis of common issues in petroleum external pipeline equipment and detailed elaboration of the process flow and practical cases of laser cladding repair, it is evident that laser cladding technology can effectively address problems such as corrosion, wear, and erosion in petroleum external pipeline equipment. It significantly extends equipment service life, ensures safety production, and reduces maintenance costs. With the continuous development and innovation of laser technology, the performance of laser cladding equipment will continue to improve, and cladding processes will become more refined. Its application prospects in petroleum external pipeline equipment repair and the entire petroleum industry will be even broader. In the future, laser cladding technology is expected to become a mainstream technology for the maintenance and repair of petroleum external pipeline equipment, providing strong technical support for the sustainable development of the petroleum industry.