the type and amount of paints, hardener, and solvents of each layer is proper and under the manufacturers recommendations.
Checking the color shade, density, and weight of the paint for each layer and reviewing its conformity according to the catalog and data sheets is also recommended. Other features to be careful about are appearance of the wet and the dry film (WFT and DFT) as well as possibility of complications for each layer preferred.
Figure 2.14 Some typical complications of the paints resulting from poor quality paint features. Weak adhesion of top coat by one manufacturer on the primer (left). Weak adhesion of topcoat to intermediate (right). Weak adhesion of intermediate to primer (down).
2.2.5.5 Paint Warehousing and Storage
One of the problems for paint application projects is the long‐time duration between the paint production and its use in the field. Most industrial users buy paint a few months before using it due to the long QC test time, and storage of paints in most projects can be up to a year. In some countries, due to political and economic reasons early forecasting and purchasing are also needed.
In the executive projects, a separate warehouse is not provided for the paints and they may be stored with other equipment in a public warehouse. The standard conditions for paint storage, such as setting the right temperature, are not indicated most of the time; this is another problem that reduces the paint quality. The method of storing and using paints during storage is very important and stated in manufacturer catalog.
2.2.5.6 Role of Executors and Contractors
One of the main problems leading to the reduction of a paints lifetime is the lack of knowledge of executors and contractors and the lack of a precise working plan. The planning and scheduling of work in many cases is based on the weather, but sometimes it is very difficult to predict the field conditions and climate change can disrupt the work schedule, accuracy, and order of work. The selection of skilled and capable contractors and providing proper facilities for implementing the standards of surface preparation and paint application play an essential role in the life of the paint. In addition to being fully aware of operation standards, the contractor must have the proper equipment to assure the health and safety of the workers and comply with the local environment regulations. Examples of unqualified workers and contractors are seen at Figure 2.15.
2.2.5.7 Surface Preparation
One of the most important phases of a paint operation is the surface preparation, which sometimes costs quite a bit. Appropriate weather conditions, good blasting materials, equipment, and proper technical skills are needed to prepare the surface. Most of the paint problems of industrial equipment are due to the weakness of the surface preparation. Some examples of these problems are observed during the field operation inspections seen in Figure 2.16. In scientific documents, special attention is referred to this issue [11].
Dry abrasion blasting with silica sand, copper slag, steel grits, etc. is the most correct and common method of field and workshop surface preparation. In a scientific research, the author investigated the surface preparation factors affecting the primer adhesion to steel substrate; the primer was an epoxy zinc phosphate with a dry thickness of 60 μm. The surface was prepared by different methods. The results are according to Table 2.1. Primer adhesion on all samples was acceptable, however, there was a noticeable difference between the adhesions of the primer to the steel surface prepared by different methods. Between some common methods of surface preparation, abrasive blasting especially by sand, to the degree of cleanness of Sa3, shows the highest quality on the paint adhesion.
Figure 2.15 Examples of unqualified workers.
Figure 2.16 Some weakness of the surface preparation. Paint application on rusted surface (left). Unsuitable abrasives and reuse of them several times (right). Weak surface preparation on weld lines (down).
Table 2.1 Adhesion of a common zinc phosphate epoxy primer on the steel surfaces prepared with several methods.
| Preparation methods | Adhesion (MPa)ASTM D4541 | Disbanding condition |
|---|---|---|
| Washing with white sprite | 1.73 | Paint layer from metal surface |
| Wire brush ST3 | 3.19 | Paint layer from metal surface |
| Weak acid washing | 2.89 | Paint layer from metal surface |
| Hard acid washing | 4.48 | Paint layer from metal surface |
| Phosphating | 4.30 | Paint layer from metal surface |
| Wet sand blast, water blast | 8 | Paint layer from metal surface |
| Dry sand blast Sa3 | 11.63 | Paint layer from metal surface |
In other research, the effect of different types of abrasives on steel preparation was investigated. Physical and chemical properties of tested abrasives are discussed in [17–19].
Properties of some abrasives are determined according to Table 2.2. In a series of tests, the author examined and compared the adhesion of a zinc phosphate epoxy primer with the same thickness on steel sheets that were prepared with these different abrasives. Results are summarized in Table 2.3.
Often, the functional performance of abrasives, such as the effect on primer adhesion is very important. It affects the mechanical stability of the film, as well as its chemical resistance, especially when the film is exposed to humid and saline environments during service time. The author investigated the effect of a number of abrasives on cured film performance by doing several tests. For that, some samples were blasted by different abrasives. They were coated with the same paint, having nearly dry film thickness. Then they were tested in a humidity chamber according to ASTM D2247, and in a salt spray chamber according to ASTM B117 [20, 21].
In these experiments, silica sand compared with different