Oil & Gas Industry
Thermal spraying has extensive and crucial applications in the oil and gas industry. In various types of equipment in this industry, thermal spraying technology effectively solves many difficulties by forming special coatings on the surface of equipment. For example, on the inner wall of pipelines, anti-corrosion coatings can resist the erosion of oil and gas media and extend the service life of pipelines. On components such as compressor blades and valves, wear-resistant coatings improve the wear resistance of components, reduce downtime due to wear and tear, ensure the continuity and safety of oil and gas production and transportation, and significantly improve overall production efficiency and reduce operating costs.
Thermal Spray Techniques Used in the Oil & Gas Industry
Flame Spraying
Process Principle:
Flame spraying is a rather traditional and widely used thermal spraying process. It utilizes the high-temperature flame generated by the combustion of fuel gas (such as acetylene, propane, etc.) mixed with oxygen to heat the spraying materials to a molten or semi-molten state. Then, the materials are atomized by compressed air and sprayed onto the surface of the workpiece to form a coating.
Application in the Petroleum and Natural Gas Industry:
It is commonly used for repairing and strengthening components that do not have extremely high requirements for corrosion resistance. For example, for the external surface protection of some ground oil and gas processing equipment, like the outer walls of oil storage tanks. For some small pipeline connection parts, such as flanges, flame spraying can be used to enhance their wear resistance and prevent mechanical damage during installation and disassembly.
Arc Spraying
Process Principle:
Arc spraying uses two continuously fed metal wires as consumable electrodes. An electric arc is generated at the ends of the wires as a heat source to melt the metal wires. Then, the molten metal is atomized by high-speed gas flow and sprayed onto the surface of the workpiece to form a coating.
Application in the Petroleum and Natural Gas Industry:
This process has obvious application advantages in the petroleum and natural gas industry. For large pipeline systems, arc spraying can efficiently prepare corrosion-resistant coatings on the surface of pipelines. For instance, aluminum or zinc coatings are sprayed on the outer surface of long-distance oil pipelines. These coatings can provide long-term corrosion protection for the pipelines because aluminum and zinc coatings will form a dense oxide film in the air to prevent further corrosion. Meanwhile, the bonding strength of the coatings formed by arc spraying is relatively high and can withstand certain degrees of vibration and impact during the transportation of the pipelines.
Plasma Spraying
Process Principle:
Plasma spraying uses a plasma arc as a heat source to heat the powdered spraying materials to a molten or semi-molten state and then spray them onto the surface of the workpiece to form a coating. The temperature of the plasma arc can reach tens of thousands of degrees Celsius and can melt almost all spraying materials.
Application in the Petroleum and Natural Gas Industry:
In the petroleum and natural gas industry, for some key components working under high-temperature, high-pressure and strong corrosion environments, such as wellhead devices and certain high-temperature and corrosion-resistant components of deep-sea oil and gas exploitation equipment, plasma spraying is a good choice. It can prepare high-performance ceramic coatings, such as alumina, zirconia and other coatings, which have excellent high-temperature resistance, wear resistance and chemical corrosion resistance and can effectively protect the components to work normally under harsh environments.
High-Velocity Oxygen Fuel Spraying (HVOF)
Process Principle:
High-velocity oxygen fuel spraying is a new type of thermal spraying process. It generates a high-speed combustion flame through a special spray gun to accelerate the spraying materials and spray them onto the surface of the workpiece to form a coating. The flying speed of the sprayed particles is quite high, which can make the coating denser and have a higher bonding strength.
Application in the Petroleum and Natural Gas Industry:
HVOF is often used to prepare high-quality wear-resistant and corrosion-resistant coatings in the petroleum and natural gas industry. For example, on the surface of the plunger of the oil well pump in oil extraction, spraying hard alloy coatings such as tungsten carbide by high-velocity oxygen fuel spraying can significantly improve the wear resistance and corrosion resistance of the plunger, extend its service life, and reduce the downtime and maintenance costs caused by frequent replacement of components. On some high-precision valve parts, the coatings prepared by HVOF can also provide good sealing performance and wear resistance.
How to choose a thermal spraying process suitable for the oil and gas industry?
Considering the Working Environment of Components
Temperature Factor
If components work in high-temperature environments, such as wellhead devices or heating furnace components in refineries, a thermal spraying process that can withstand high temperatures should be chosen. Plasma spraying is a great option. It can use materials with high melting points like zirconia to prepare coatings, which can endure temperatures as high as 1000 °C or even higher, effectively protecting the components from high-temperature oxidation and hot corrosion.
For components with relatively low working temperatures, such as ground pipelines, flame spraying or arc spraying processes may be sufficient to meet the requirements. They can provide certain temperature resistance performance and are relatively cost-effective at the same time.
Corrosion Environment
In strong corrosion environments, such as the equipment on offshore oil and gas production platforms that have long-term contact with seawater and oil and gas containing corrosive chemical substances, coatings with excellent corrosion resistance are needed. High-Velocity Oxygen Fuel Spraying (HVOF) and plasma spraying can prepare dense ceramic or alloy coatings. For example, spraying tungsten carbide-cobalt coatings by HVOF has good resistance to seawater corrosion and oil and gas corrosion.
For some inland oil and gas fields where the corrosion environment is relatively weak, mainly with the corrosion caused by formation water and a small amount of acidic substances in oil and gas, arc spraying zinc or aluminum coatings can provide good anti-corrosion protection through the sacrificial anode method, and the cost is relatively reasonable.
Wear Situation
For components that endure severe wear, such as plungers of oil well pumps and compressor blades, a process that can prepare coatings with high hardness and high wear resistance should be selected. High-Velocity Oxygen Fuel Spraying is one of the ideal processes for preparing wear-resistant coatings. It can spray hard materials like tungsten carbide and chromium carbide onto the surface of components at high speed to form dense and firmly bonded wear-resistant coatings, greatly improving the wear resistance of components and reducing equipment damage and maintenance costs caused by wear.
If the wear situation is relatively light, the metal coatings prepared by flame spraying or arc spraying can also improve the wear resistance of components to some extent.
Considering the Shape and Size of Components
Large Components
For large pipeline systems (such as long-distance oil pipelines), arc spraying is a relatively suitable process. Arc spraying equipment is relatively simple and easy to operate. It can quickly spray on the large surface area of pipelines. Moreover, the efficiency of arc spraying is high, and it can complete the preparation of large-area coatings in a relatively short time, reducing construction time and cost.
For large oil storage tanks and other equipment, flame spraying can also be used for external surface protection. Its equipment has good mobility and can be conveniently operated around large equipment.
Small or Complex-Shaped Components
For some small and complex-shaped components, such as the fine structures inside valves and instrument sensors, plasma spraying or high-Velocity Oxygen Fuel Spraying is more appropriate. These processes can precisely control the direction and speed of spraying particles, enabling the coatings to evenly cover the surfaces of components with complex shapes. For example, plasma spraying can adjust the angle of the spray gun and spraying parameters to prepare high-quality coatings on the valve spool and valve seat surfaces, improving the sealing performance and wear resistance of the valves.
Considering Cost Factors
Equipment Cost
Flame spraying equipment is relatively simple and has a low price. For some small enterprises or application scenarios where the requirements for coating performance are not particularly high, flame spraying equipment is an economical choice.
Plasma spraying equipment and high-Velocity Oxygen Fuel Spraying equipment are relatively complex and have high prices. However, they can prepare high-performance coatings. For some key components and application scenarios with extremely high requirements for coating quality, the investment in such equipment is worthwhile.
Operating Cost
The operating costs of flame spraying and arc spraying mainly include the expenses for fuel, electrode materials, and compressed air. The operating costs of these processes are relatively low. In some large-scale projects that are sensitive to cost, such as the protection of long-distance oil pipelines, the operating cost advantage of arc spraying is relatively obvious.
Plasma spraying and high-Velocity Oxygen Fuel Spraying need to consume a large amount of electrical energy and expensive spraying powder materials, so the operating costs are high. However, considering that they can prepare high-quality coatings, for some components with extremely high performance requirements, such as the key components of deep-sea oil and gas production equipment, the high cost investment can be compensated by extending the service life of components and improving the reliability of equipment.
Considering Coating Performance Requirements
Coating Bonding Strength
If there is a high requirement for coating bonding strength, such as on the compressor blades that rotate at high speed, the coating needs to be firmly attached to the component surface to prevent it from falling off during high-speed rotation. The coatings prepared by high-Velocity Oxygen Fuel Spraying and plasma spraying processes have relatively high bonding strengths and can meet this requirement. High-Velocity Oxygen Fuel Spraying can make spraying particles impact the component surface at high speed to form a good mechanical bond; plasma spraying can make the coating materials have physical and chemical interactions with the component surface to improve the bonding strength.
The coating bonding strengths of flame spraying and arc spraying are relatively low, but through appropriate surface pretreatment and post-treatment processes, they can also meet certain usage requirements.
Coating Density and Porosity
For some components that need to prevent liquid or gas penetration, such as the inner layer protection of oil storage tanks, the coatings need to have a low porosity and high density. Plasma spraying and high-Velocity Oxygen Fuel Spraying can prepare relatively dense coatings, reduce porosity, and improve the anti-permeability performance of the coatings.
The coatings prepared by flame spraying and arc spraying have relatively high porosities, but their performance can be improved through subsequent sealing treatment.
The service life thermal spraying process on the equipment in the oil and gas industry
Factors Affecting the Service Life of Coatings
Coating Materials
Different coating materials have significant differences in performance. For example, wear-resistant coatings prepared by High-Velocity Oxygen Fuel Spraying (HVOF) using hard alloy materials like tungsten carbide on components such as plungers of oil well pumps can have a service life that is 3 to 5 times that of ordinary uncoated components according to the actual working conditions. This is because tungsten carbide coatings have high hardness and good wear resistance, and can withstand the wear caused by the frequent reciprocating motion of the plungers of oil well pumps.
For corrosion-resistant coatings, such as thermally sprayed aluminum or zinc coatings on the outer surface of land oil pipelines, their service life is generally around 10 to 20 years. Aluminum and zinc coatings can protect the pipelines through the sacrificial anode method and form dense oxide films in the air to delay the corrosion process of the pipelines.
Working Environment
High-temperature environments will accelerate the aging and failure of coatings. For example, on the heating furnace components in refineries, if zirconia coatings prepared by plasma spraying are used to resist high-temperature oxidation, under normal working temperatures (800 – 1000 °C), the service life of the coatings may be around 5 to 8 years. However, if the working temperature exceeds the designed range, the service life of the coatings will be significantly shortened.
In strong corrosion environments such as offshore oil and gas production platforms, the equipment is eroded by both seawater and oil and gas containing corrosive chemical substances. For ceramic coatings sprayed by HVOF, under normal maintenance conditions, the service life may be around 8 to 12 years. If maintenance is improper, such as the coating surface being scratched or being soaked in seawater for a long time, local failure of the coating may occur within 3 to 5 years.
Coating Quality
Quality indicators of coatings such as bonding strength and porosity have a significant impact on the service life. When the coating has high bonding strength and low porosity, it can better resist the erosion and wear of the external environment. For example, if the coatings prepared by plasma spraying have a good bonding strength (greater than 40 MPa) and a porosity lower than 5%, their service life on petroleum and natural gas equipment will be about 30% to 50% longer than that of coatings with poor bonding strength and high porosity.
Approximate Service Life of Coatings on Different Equipment
Pipelines
For the outer surface of land oil pipelines, if zinc coatings are applied by arc spraying, the service life can reach 15 to 20 years under normal environments. For submarine oil pipelines, multi-layer composite coatings are used, such as first applying aluminum coatings by arc spraying and then using plasma spraying to apply ceramic coatings as a sealing layer on top. Their service life may be around 20 to 30 years and can effectively resist seawater corrosion and the scouring of the complex submarine environment.
Compressor Components
When tungsten carbide coatings are sprayed on compressor blades by HVOF, the service life is generally around 8 to 12 years. The coatings can effectively resist the friction and wear caused by the high-speed rotation of the blades with gases and impurities, as well as the corrosion of the corrosive components in oil and gas on the blades.
Valves
Ceramic coatings are applied on the valve spool and valve seat inside the valves by plasma spraying to improve wear resistance and sealing performance. Under normal operating conditions, the service life can reach 10 to 15 years. The coatings can reduce the wear during the opening and closing of the valves and prevent the leakage of media.