by Miguel Turri*
Water is a strategic resource for many countries. Many wars, such as the Six Days in the Middle East, have been fought in order to gain better access to vital liquid. Thanks to the growth of the population and the activities they develop, the requirements related to water have increased, forcing the development of new distribution systems that allow it to be taken to the areas that require it.
In the case of Venezuela, several projects related to the issue of the distribution of drinking water are currently being developed. Such is the case of the "Bolivarian Aqueduct" started in 2004, which represents the largest and largest hydrological work in that country, having an extension of 235 kilometers of steel pipes 12 meters long and 56 inches in diameter. This places it as the largest project in the country. Its hydrological flow will be 2,500 liters per second, starting from the Matícora reservoir near the Mene Mauroa region to the cities of Punto Fijo and Santa Ana de Coro, in the state of Falcón.
The construction of a work of such magnitude, needs a thorough study of the characteristics and requirements that the idea of transporting drinking water through buried pipes contains. Beyond the considerations of construction and installations, the conditions of maintenance and useful life of the work must be taken into account.
In this sense, the proper selection of materials for construction is of the utmost importance when devising this type of project. Especially if it is considered that a metal structure (the pipe) is being integrated into the same space together with a liquid (water), that is, the perfect ingredients for the corrosion process to be present immediately. In addition, there is also the problem of chemical agents dissolved in the earth that will come into contact with the outer surface of the aqueduct.
Coating scheme
The simplest and most economical way to protect a metal structure from corrosion is to apply a paint system that is capable of withstanding the working conditions under which the structure will be subjected for an extended period of time.
The aqueduct specifications required the coatings to comply with the ANSI/AWWA C210 standard "Liquid-Epoxy Coating Systems for Interior and Exterior of Steel Water Pipelines". This standard includes from the type of paint that must be used for the interior and exterior of the pipe, through the type of surface preparation that must be carried out, to the inspection methods to be carried out to ensure the adequate performance of the system.
The coating that is used for the corrosion protection of the interior of the pipes must be formulated based on epoxy resins, provide lasting corrosion protection and must not incorporate any type of contaminant to the water that circulates through it, since it will be used for human consumption.
The Venezuelan standard COVENIN 3739:2002 "Epoxy Resins and Polymers Based on Epichlorohydrin Used for the Elaboration of Sanitary Coatings" of the Ministry of People's Power for Health, specifies that this type of coatings, once they have cured, must contain less than 1 p.p.m. of a chemically toxic agent called epichlorohydrin.
Additionally, this product has to reach a minimum dry film thickness of 8 mils (200 microns), according to the project specification. For this case, a product was supplied which is a two-component epoxy coating cured with adduct-amine. This product has 70% solids by volume and is capable of reaching dry film thicknesses between 5 and 12 mils (125 and 300 microns). It has the approval of the "National Sanitation Foundation" (N.S.F.) and by the "Ministry of People's Power for Health" to be in contact with drinking water.
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For corrosion protection of the outside of the pipes should also be used a coating formulated from epoxy resins, reaching a minimum dry film thickness of 16 mils (400 microns), as specified in the project.
But in this case, the working environment that must support such a coating is totally different from that which exists inside the pipe, since the aqueduct will be underground. This means that the coating selected for this application must be resistant to moisture and the diversity of chemical agents present in the earth along the path of the aqueduct. In this sense, a product was supplied that was an epoxy pitch cured with amine that has excellent chemical resistance. This coating, thanks to its formulation, has 78% solids per volume and is capable of reaching dry film thicknesses between 8 and 20 thousands in a single hand (200 and 500 microns).
Application
The start-up of the painting works was an engineering challenge, since it was necessary to adapt the application equipment to the coatings, in order to meet the requirements of the project. In this case, the painting process is carried out thanks to an airless application system and is executed in two stages: first the inside of the pipe is painted with Amercoat 395HS and after reaching the drying to the handling of this product, the Amercoat 78HB coating is applied to the outside of the pipes.
In general, the application process consists of a spear (where the nozzles are fixed) that moves along the pipe applying the paint, while the tube rotates on its own axis. This implies that there are at least five variables that must be controlled to meet the requirements of the project, which are:
Speed of advance of the spear.
Speed of rotation of the tube.
Pump pressure.
Nozzle used.
Nozzle-Substrate distance.
Surface pre-treatment
Another aspect of utmost importance to ensure the proper performance of the paints is the surface preparation that must be carried out to the pipes before the application of the coatings. In this case the surface preparation required by the project is an SSPC-SP 10 (cleaning with abrasive jet to almost white metal). Equipment is used that shoots pellets (metal particles) against the surface of the pipe, in order to eliminate any presence of rust on the structure and generate the appropriate anchor profile required by the painting system, in order to ensure that during the application and commissioning of the pipes, the coatings do not present any type of failure.
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For this, the team of technicians together with the personnel of the companies that manufactured the pipes, were in charge of working from the beginning of the project to achieve the optimal working conditions that not only met the requirements of the project, but were also in tune with the productive cycle of each of the construction companies.
At the beginning of the project, work began with one of the tube manufacturers, which although it was operational, did not have all the necessary equipment to develop the painting work required by the work.
The technical staff was in charge of adjusting one by one the variables of the process, modifying parameters and operating conditions, not only of the application equipment, but also of our products. No detail was overlooked until our painting, together with the mechanical and human team of the tube manufacturing company, worked in a synchronized way.
The technical staff was involved in the production process of the company from the arrival of raw materials for the manufacture of the pipes, through the processes of inspection and quality control, to the delivery of the finished product.
During the execution of the works, the presence of technical personnel of the coating manufacturer has been constant, to attend to any type of concern that may arise in the process of applying the paints. Additionally, courses have been given for workers in the coating area, which are aimed exclusively at the painting system of the "Bolivarian Aqueduct".
These courses are entitled ENCAPI, "Training and Training of Painters. System for Drinking Water Pipes-AMERON, Complying with the AWWA C210 Standard". The objective of this is to train the staff, from the painters, through the quality control inspectors, to the superintendents of the painting area, in the most important aspects related to the application of each of the coatings used for the pipes that have made up the project. The courses are evaluated, in order to ensure that the information has been assimilated and those participants who pass, receive a certificate that accredits them as qualified personnel to work on that work.
Currently the project has completed its first phase of manufacture and installation, which is made up of a 60-kilometer stretch of pipe. Once the work is completed, it is estimated that approximately 210,000 gallons of paint will have been used, which translates into an investment of around 14.8 million dollars in the area of industrial coatings alone.
If it is considered that the entire project has contemplated a cost close to 430 million dollars, the investment in painting does not exceed 3.5% of the total budget. But what an important role does the corrosion protection of the paint system play in ensuring the uninterrupted supply over time of drinking water for the population.
Thinking about the future implies taking into account the challenges that tomorrow will bring, it is trying to imagine how to grow and improve the quality of life of people. This is precisely what is sought when a work is projected that wants to improve the development and quality of life of the peoples, such as the construction of the "Bolivarian Aqueduct", which beyond supplying a significant amount of drinking water to western Venezuela, raises the possibility of the development of new projects for the benefit of the people.
* Technical Support Department, Pinturas AYA. [email protected]
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