Learn how the surface pretreatment, application of coatings and finishes was carried out in order to prevent corrosion in this project that was carried out in Venezuela.
by Eng. Charly Hamoni K*
The company Cantv-Movilnet, at the beginning of 2005 promoted a project that was carried out by the company Manufacturer of Telecommunications Towers, called "Construction and Coating of Telecommunications Towers of CANTV-MOVILNET". This covered the transmission network of fixed and mobile telephone signals in the states of Anzoátegui, Apure, Barinas, Bolívar, Carabobo, Falcón, Lara, Miranda, Portuguesa, Sucre, Táchira, Vargas and Zulia, among others, and of which our company was the main supplier.
Telecommunications companies have seen the need to expand their coverage network and services by installing new equipment that meets customer requirements, motivated by the accelerated growth of technology and users who seek to obtain a service that is not only efficient, but also fast and simple, in order to communicate the aforementioned states with each other and with the rest of the national and international territory.
This project had the commercial and technical visits of our technical team, offering support and training before and during the coating of the structures to the contractor company and the personnel in charge of carrying out the application of the coatings.
More than 30 telecommunications towers were painted in new galvanized steel, with heights between 24 and 100 meters and between 3 and 40 tons of galvanized steel, both monopoly towers and self-supporting towers. The coating project was valued at more than 6.2 million dollars, where coating and application formed the bulk of the operation. Finally the project required a total amount of 56,000 gallons of paint, between bottom and finish.
Surface pretreatment
Prior to the coating process of the galvanized structure, the surface preparation was carried out with the SSPC-SP2 methods cleaning with manual tool and / or SSPC-SP3 cleaning with mechanical tool, until creating the necessary roughness to promote the adhesion of the bottom to the surface, but without damaging the galvanizing layer.
The term galvanized is used almost exclusively to describe the formation of a zinc coating on steel parts, by immersing them in a molten zinc bath. Zinc binds to steel tightly, forming layers of multiple steel-zinc alloys on the surface, with varying degrees of zinc content. This metal has special electrochemical properties (barrier protection, sacrificial anode), being more oxidizable and tends to corrode first than steel.
The galvanizing has a very smooth final finish, which makes it difficult to adhere to the coating, which is why the surface preparation is carried out to the galvanized structure. If a preparation of a higher degree were to be carried out than that carried out for the project in question, there could be a risk of damaging the galvanizing layer and therefore losing the protection it provides.
Coating scheme
Usually in projects of galvanized structures, a system is recommended that involves as a background a tolerant surface coating, which is able to adhere to substrates with low preparation. There is also the option of an anchor promoter bottom that imparts the necessary roughness for the back layer to adhere.
For this case, we decided to carry out an initial test with different coatings of our product line in order to find the one that offers the best protection, and especially the required adhesion characteristics. These tests were carried out in the field in the facilities of the tower of Lomas de Níquel, Miranda State and simultaneously in our laboratories supported by the results, our technical support team chose the paint system described in the following table.
The Amercoat 71 bottom is a very versatile epoxy coating, suitable for a wide variety of substrates including galvanized, which meets the thicknesses required by the project. It provides maximum weather resistance and adheres very well to surfaces prepared to the recommended grade described above.
The recommended finish is a polyurethane coating, resistant to UV rays, with outstanding resistance to weathering, abrasion and a wide variety of corrosive environments, with excellent color and gloss retention. The Amercoat 450HS is manufactured in a wide variety of colors, which adapt to the customer's requirements. In the telecommunications towers of CANTV-MOVILNET, the colors white and red were used in alternating stripes, starting from the base with the red color according to the International Standard Obstruction Parking and Lighting and the National Official Gazette # 5044 of Signaling.
Another factor that we take into account when recommending the system is that the contractor applies the brush coatings. Both products, both the Amercoat 71 bottom and the Amercoat 450HS finish, are applicable with this method and have good broachability. The enamel when applied provides the optimal leveling so that when the paint finally heals it presents a uniform and high-gloss finish.
Why line galvanized telecommunication towers? The objective of painting the towers is primarily to protect the structures against abrasion and the aggressive environment to which they will be subjected from the base to the tip, providing greater durability over time and thus prolonging the life of the same, increasing the time intervals to perform the maintenance of the structures.
The galvanized telecommunications towers have a duration of approximately 20 years and when coated the duration range is extended between 30 and 35 years depending on the environment to which they are subjected and to comply with the scheduled inspections and maintenance plan. Duplex paint schemes involving galvanized structures and cladding, such as the one used for this project, are at the top, being the one that provides the greatest protection and durability of the structures over time.
Projects like these represent large investments in the present that see their immediate and future fruits.
* Technical Support Department, AYA Paints.
