By Abel De la Cruz*
Anticorrosive maintenance works through the application of protective coatings in our environment, commonly suffer from engineering studies for their execution, unlike the treatment of anticorrosive protection of surfaces in new construction works, whose technical file (specifications and procedures) is part of the engineering study of the work.
It is common to find that anti-corrosion maintenance projects of the productive infrastructure or services do not have an adequate allocation of economic budget, which allows to elaborate previous studies with the diagnosis and evaluation of the state of conservation of the infrastructure, as well as with the procedures for the planning and execution of a comprehensive maintenance program, including the terms of quality assurance and the industrial safety and hygiene measures that these require.
Process
In our consulting experience in corrosion protection, we have found that anti-corrosion maintenance of surfaces with paints, in a large number of industrial and service companies, is not yet given the same priority compared to mechanical and electrical maintenance, except when the need for immediate treatment arises or when coating failures put structural or operational aspects at risk.
Effective maintenance planning requires that through periodic inspections and with adequate records, a detailed knowledge of the conditions in which the plant facilities, structures, equipment, etc. are located.
In this way, the magnitude and depth of the treatment will be known, the need for the replacement of structures or mechanical repairs, the order of priority to execute the works, especially in companies with extensive infrastructure.
To carry out the development of the technical file, engineers in the maintenance and project area must have specialized knowledge in corrosion and protection techniques, as well as at least three years of experience in inspection and application of industrial paint. Below we propose the development of the following field activities:
1) Carry out the calculation of the structural areas, in order to obtain the extension and approximate valorization of the maintenance. The areas that will receive maintenance can be classified according to:
a) Type of work to be carried out (cleaning of dust and grease, resane painting, total painting, etc.)
(b)Type of surface
(c)Equipment
d)Painting system
2) To draw up isometric diagrams/plans of the equipment and structures of the inspected equipment in which the area to be repaired can be marked (especially when the damage is punctual or scarce). In case the damage is extended or generalized in the structure or equipment, this punctual identification will not be necessary. Schemes or isometrics shall indicate the following:
a) Identification of the structure or equipment.
b) Identification of the fault found.
c) Record of the thicknesses of old paint measured.
d) Area to be repaired.
e) Color or type of paint to be used.
It can also be used as an alternative for the schematization of equipment, the photographs of digital preference.
3) Identification of areas that have suffered corrosive deterioration or attack of the medium, both on the base metal substrate, and on the painted areas in each of the service units, and perform the following inspection tasks:
Identification and sizing of the fault of the old paint
This work is carried out by means of a visual inspection and five-magnificators may be used, the inspection must be exhaustive and the type, extent and degree of failures must be determined, such as:
Rusting: ASTM D 610, ISO 4628-3
Degree of tipping assessment: ASTM D 659, ISO 4628-6
Check Grade Assessment: ASTM D 660
Cracking grade assessment: ASTM D 661, ISO 4628- 4
Blistering grade evaluation: ASTM D 714, ISO 4628- 2
Scaling/flaking grade assessment: ASTM D 772, ISO 4628-5
Measurement of applied paint thicknesses
In the case of equipment and metal structures in general, the necessary amount of readings must be taken to determine the remaining thickness, so that the real state of the coating and the maintenance and correction work to be carried out are determined.
The SSPC-PA 2 Standard: "Measurement of Paint Thickness with Magnetic Gages", describes the methodology for measuring the dry film thickness of a coating and defines the number of points to be measured based on the area and geometry of the surface.
Assessment of accession
The corrosion protection of steel through the use of coatings depends on a good adhesion of the paint to the substrate. The adhesion test allows you to decide whether or not to remove the old coating before painting.
The evaluation of this factor is of great importance in the durability of the paint system and is destructive in nature. Field trials that are generally used to measure the adhesion of coatings are as follows:
The "Standard Test Methods for Measuring Adhesion by Tape Test" ASTM D 3359 A (for X-Cut) and B (for Grid Cutting) (ISO 2409)
The "Standard test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers" ASTM D 4541(ISO 4624)
The adhesion test, according to ASTM D 3359, is performed by the cutting method (with razor) in the form of a cross or grid depending on the dry film thickness of the paint system. The results are qualitative based on a visual scale with six levels or degrees of adhesion, evaluating the degree of chipping along the edges of the cuts.
The tensile adhesion test, according to ASTM D 4541, consists of gluing a metal device to the surface of the coating perpendicularly with an epoxy adhesive and then measuring the force needed to tear off the applied paint.
Values higher than 3.0 Mpa are commonly specified as acceptable for corrosion protection paint systems in industrial severe media C 5-I, according to the ISO 12944 classification of corrosive environments. The acceptability values will depend on the type of service (atmospheric, rural, marine, immersion, etc.) to which the paint system is subjected (ISO 20340, ISO 12944-6).
4)Evaluate and determine the necessary factors that influence the selection of paints for maintenance work:
Environmental or climatological conditions.
Corrosive aggressiveness of the medium (ISO 12944).
Facilities for applying paint and preparing the surface.
The name and/or type of the old painting. Not only to evaluate its performance but to avoid incompatibility with other paints and the consequent premature failures in case repainting is carried out without total elimination of the old paint.
Surface preparation achieved in the previous painting. Perhaps it is the most important factor that affects the duration of the system, since knowing the procedure applied we can evaluate and diagnose its results.
System service time. It is equivalent to the exposure time of the system from the previous painting work to the date on which the maintenance will be carried out.
Based on the results and their interpretation, the Technical File for Anticorrosive Maintenance is prepared and prepared, which describes in detail the extent of the structures or surfaces that will receive the treatment, the state of the coating and the substrate, the rules of surface preparation, the methods of application of the paints, the maintenance painting procedure, inspection standards, quality control in each of the process activities and industrial health and safety standards to protect personnel and the environment, etc.
* Manager AmericanConsult Peru. [email protected] http://www.americanconsultperu.com
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