Corrosion Policy Decision Making. Группа авторов
for this propose at industrial complexes [10].
There is a lot of variety of liquids inside the tanks in a petrochemical complex. In addition, there is a huge difference in the internal ambient temperature of containers, vessels, tanks, etc. in industrial facilities. All of these environmental parameters must be considered when choosing paint and coatings for each application.
Recognition and classification of atmospheric and/or immersion environments, determination of their degree of corrosion, and choice of proper paint systems for each class is briefly explained in some standards [11, 12].
By measuring environmental characteristics and operating conditions such as substrate temperature, it is possible to extract the proper type and thickness of a suitable paint system and the number and thickness of layers based on standards [11].
Users must have knowledge of the standards for choosing the suitable paint systems for various industrial applications. They must be familiar with the environmental factors affecting the early degradation of paints.
Some of the factors needed to consider for choosing paint systems are as follows.
1 The substrate surface conditions;
2 environmental classification and determination of the environmental corrosion class;
3 the operating temperature of the equipment and the allowable service temperature;
4 the effect of UV rays;
5 the presence or absence of CP of substrate;
6 optimal life of the paint system;
7 possibility of workshop and/or field application;
8 the need for a special color of paint for luxury and/or identification;
9 health, safety, and environmental restrictions;
10 surface preparation and application conditions;
11 previous experiences;
12 possibility and cost of repairs; and
13 paint properties.
Lack of knowledge on the properties of paints and improper use of them is another major cause of paint degradation. If the inspectors and consultants of the industrial production of equipment do not have accurate information of the properties of ordered paints, unsuitable choices will cause premature destruction of the paints. For example, epoxy paint that is used in the open industrial environment of an oil refinery and exposed to direct sun radiation is rapidly damaged due to the weak resistance of the epoxy to the ultraviolet rays of sunlight (Figure 2.10).
In addition, due to the lack of knowledge about the method of curing ethyl silicate paint (requires high humidity for curing), its use in an industrial complex located in a dry environment has led to lack of primer curing, and ultimately the destruction of the paint system. This mistake was repeated for three times (Figure 2.11).
Therefore, in order to reduce or avoid paint problems, it is necessary for inspectors and users of industrial paints to have enough information about the properties of paints. Many documents have written with the knowledge of the type, classification, and use of paint [11, 13, 14].
Figure 2.10 Paint checking due to weak resistance of the epoxy to the sunlight in an oil refinery.
Figure 2.11 Lack of curing of ethyl silicate primer used in dry area.
The four main components of industrial paints, including pigments, binders, solvents, and additives play their own special role in paint performance. In addition, paint systems consist of appling industrial paints in continuous and sequential layers, each layer having certain properties.
Pigments play an important role in improving the quality of paint. Although some pigments have decorative properties, they also play an important role in optimizing the texotropic properties and rheology of the paints, such as reducing sagging and dripping problems. The strength of the paint and the gloss and hiding properties on the previous layer are other characteristics that are enhanced by the pigments. They also play an important role as corrosion inhibitors in the primer.
In the simplest classification, pigments are divided into two main groups; pigments and extenders [7]. Pigments include zinc powder and zinc oxide, iron oxides, titanium dioxide, lead chromate, basic lead‐silico chromate, molybdate, zinc chromate, lead cyanimides, zinc powder, blue iron (Prussian blue), aluminum pigments (powder and paste), bronze, mercury oxide, etc. and their chemical properties are explained in handbooks and factory catalogs.
Zinc powder is one of the most common primer pigments. It is sometimes packaged as a third part for primers. Often, not observing the exact mixing ratio or insufficient stirring leads to poor wetting and causes a complication in the dry film (Figure 2.12).
Titanium dioxide is one of the most common pigments used in paints. Titanium is present in the structure of anatase and rutile. The rutile type consists of a denser crystal lattice than anatase, and it has a higher refractive index, and this type has good resistance to deterioration. The use of anatase as pigments of the top coat paints leads to severe chalking when the system is expose to sunlight (Figure 2.13).
Extenders are solid minerals that may added to paint formulation along with the pigments to modify some of the properties of the paints as well as to reduce the cost of production. They are also used to improve the following properties, and optimizing quality of paints.
1 Adjusting and optimizing the ratio of pigment to binder to meet suitable PVC.
2 Increasing the physical strength of the paint film.Figure 2.12 Poor wetting and undesired mixing of primer components.Figure 2.13 Chalking when the system exposes to sunlight because of the use of anatase Tio2 pigments of the top coat.
3 Improving the rheological properties of paint.
4 Increasing the resistance to ion penetration.
5 Reducing the effect of microbial agents.
6 Optimization of optical properties.
7 Resistance or electrical conductivity.
8 Thermal resistance and fire retardant development.
Some extenders include calcium carbonate, white carbonate, aluminum silicate, magnesium silicate (talc), mica, silica, calcium sulfate, asbestos, barium sulphate, and zinc sulphate. Their chemical properties described in the reference [7].
Organic pigments and metal pigments also used in a few applications whose properties are described in some sources [7, 15]. For example, the use of the pigments of aluminum, copper, nickel, iron, stainless steel, zinc, tin, etc. in paints were described [7].
The resin is most important to form a uniform and continuous film on the metal surface. This component used in the paint formulation allows for adherance to the substrate and allows the continuity of paint components to bond in the dry film. It should also create a dry film that prevents the diffusion of water vapor and various corrosive contaminants from the environment