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What do we know about the gas-thermal spraying?

The gas-thermal spraying helps meet the challenges of multiple extension of the service life of oil and gas, metallurgical, chemical and petrochemical equipment for the account of reduction of the intensity of wear and corrosion of individual parts.
According to L.Kh. Baldayev, Director General of TPCS Limited, advanced methods of application of gas-thermal coatings include gas-plasma and HVOF (high velocity oxygen fuel) processes.
The purpose and application domain of plasma spraying of powdered materials is application of coatings with special properties: (corrosion-resistant, heat-resistant, thermal-protective, antifriction, etc.) during manufacturing and repair of parts and assembly units exposed during operation to high loads and intensive wear.
High velocity oxy-fuel (HVOF) flame spraying is used for application of overdense protective coatings with high adhesive characteristics and special properties during manufacturing and repair, including local, of machine parts and assembly units.

The economic effect is achieved for the account of the following factors:

1. creation of a thin coating with tailor-made properties is much cheaper than manufacturing of
an entire part from expensive alloys;
2. weight reduction in the large allows energy saving;
3. longer interrepair cycles make it possible to reduce down time and costs of assembly and
pre-commissioning;
4. maintainability of coatings allows saving the time of waiting for a new part and achieving an
equivalent service life at 30-50% of the cost.

Many engineering processes and know-how owned by TPCS Limited have no match in Russia and CIS countries, and globally are used by a limited number of companies. It relates, in particular, to high-velocity spraying techniques where the gas flow velocities exceed 2,000 m/s, and the coating density reaches 99.9% of the base material density.
For example, in 2003, Technological Protective Coating Systems suggested a new solution for protecting inner surfaces of the columns by application of an anticorrosive wear-resistant coating using the gas-thermal spraying method. Based on the test results, high-alloy stainless steel was selected and the coating was applied using a HVAF (high velocity air fuel) thermal spraying technique. The operating principle of the installation is based on burning fuel in a special combustion chamber exhausting a gas jet having a velocity of up to 2500 m/s. The powdered material fed into the gas flow is heated up and accelerated to velocities of about 700-800 m/s. Arriving at a work piece, powder particles possessing high kinetic energy form a dense coating with high adhesive characteristics. The volume fraction of air in the coating is no more than 1%, and the adhesion to the base exceeds 80 MPa. The coating has many layers; therefore, there is no through porosity. The strengths of this approach also consists in that the method can be conditionally called a "cold technique", i.e. when coatings are applied, parts heat up to no more than 120-150°С. This approach avoids any phase transformations in the base metal during coating application.
It was also TPCS who developed a technique and fabricated a unique robotic center for in-place application of protective coatings to the inner surfaces of the columns by the high-velocity gas-thermal spraying method without.
Based on the results of a check for the period of more than three years' operation of absorber columns repaired using the gas-thermal spraying method, a conclusion was drawn about the cessation of the process of corrosive-erosive wear, which is less than 0.1 mm compared to the annual 8-10 mm for uncoated columns.
During operation of the columns, the coating behavior is regularly observed, and the results of the first columns operation revealed a possibility of development of underfilm corrosion in the bottom part of the column, in the liquid phase area. In this connection, a new composition was suggested which is essentially a two-layer coating with an undercoat that is less prone to the development of underfilm corrosion. Application of a two-layer coating made it possible to increase the repair interval of the coating from 3 to 5 years.

In such a way, the use of the above method allows:

• Reducing the cost of purchases of new columns (formerly, the columns were subject to replacement every 6 years).
• Reducing the cost of installation/removal and pre-commissioning.


Reference materials:
1. New Equipment and Technologies of the Gas-Thermal Spraying. L.Kh. Baldayev, Cand. Sc. (Engineering) // "Tekhsovet" journal, March 3, 2007//
2. Protection of Oil and Gas Equipment and Facilities Against Corrosion Using Gas-Thermal Spraying Methods. //A.Z. Lurye. Business Development Director, Technological Protective Coating Systems Limited, V.V. Geraskin Executive Director, Technological Protective Coating Systems Limited.