surface. A noteworthy point about carbon steel samples prepared with copper slags was that their particles trapped in all samples. Slag particles were observed which could not washed out even by using air pressure (five bar pressure) and washing with solvent. However, for samples prepared with silica sand, leaving excess particles from the surface with compressed air were easily and completely removed from the surface. All samples were coated with the same paint layer with a similar dry film thickness.
Table 2.2 Properties of tested abrasives in blasting.
| Test | Standard | Result for all samples |
|---|---|---|
| Hardness (mohz) | SSPC‐AB‐1 | At least 6 |
| Weight change on ignition | SSPC‐AB‐1 | Max. 5% |
| Oil content | ASTM D‐7393 | No visible |
| Specific gravity | ASTM C‐128 | Min. 2.5 |
| Moisture content | ASTM C‐566 | 0.5%< |
| Water soluble contaminants | ASTM D‐4940 | <1000 μs/cm |
Table 2.3 Effect of abrasives on adhesion of primer at humid and salty environments.
| Abrasives | Adhesion test before exposureASTM D4541Psia | Adhesion test; 1500 hours salt spray and 24 hours dryingASTM D4541 Psia | Adhesion test; 1500 hours humidity and24 hours dryingASTM D4541Psia |
|---|---|---|---|
| Copper slag Sample A | 1687 | 528 | 1603 |
| Copper slag Sample B | 1541 | 486 | Test error |
| Copper slag Sample C | 1569 | 388 | 1160 |
| Copper slag Sample D | 1446 | 516 | 1223 |
| Cupper slag Sample E | 1355 | 422 | 1306 |
| Supper slag Sample F | 1525 | 1329 | 1385 |
| Silica sand Sample G | 1687 | 1855 | 989 |
| Silica sand Sample H | 1900 | 1917 | 1898 |
As seen in the Table 2.3, after complete curing and before beginning the corrosive tests, the adhesion of all samples was in acceptable range. Separation of all samples were with an interlayer that did not return to the abrasive quality. The sheets were prepared with different abrasives, placed and tested for resistance in a humidity cabin environment at 100% humidity, and similarly in a salt spray chamber for 1500 hours, separately. The results were interesting; the samples prepared with abrasive silica sand showed a significantly better resistance than others. In addition, they had more strength adhesion at the end of the laboratory exposure tests. The results are shown according to Table 2.3. Therefore, type, shape, and size of the abrasive material have a significant effect on long life of paints in the abrasive blasting method.
2.2.5.8 Technical Painting Operations
Painting application requires special skills; the inexpert technician can lead to the destruction and complication of the film. Examples of paint application problems are shown in Figure 2.17. It is necessary for the executors be aware of the causes of paint defects and the method of avoiding, eliminating, and correcting these complications.
Figure 2.17 Some examples of paint application problems. Rusting on primer due to thin primer layer (a). Running of paint and settling of dirt due to adjacent blasting operation (b).
Many paint defects are mainly related to the method of their application. The wrong choice of hardener and thinner for paints, incorrect mixing of paint components, and wrong choice of different layers of a paint system are the most common causes of complication in paint application. Accuracy at the important points in the catalog can cut problems. Lifting, orange peel, overspray, pinholes, spatter coat, etc. are some of the complications that may occur due to these problems [7].
Excessive hot or cold temperature of the substrate, high humidity, dust, and local pollution are other factors that may cause complications during paint application. Adherence to implementation instructions greatly reduces these problems. Complications such as amine blushing, blushing, holidays, rusting, etc. are observed in these conditions [7].
Inadequate regulation of paint viscosity and spraying pressure in airless spraying, as well as inadequate air‐to‐paint ratio in air spraying methods are other causes of complications during application. These factors lead to difficulty in achieving the right thickness as well as complications such as sagging and running, etc.
2.2.5.9 Inspection and Management
Industrial paint inspection plays an important role in the useful life of paints and paint systems. Unfortunately, in certain circumstances, surface preparation and paint application is performed without the necessary care by inspectors. For example, for problems referred to in Figure 2.18, the paint was applied only on visible sections. In addition, the primer was applied to the previous existing paint, which is another gross mistake of inspection.
On the other hand, a number of refinery project managers have no technical approach to the issue of paints and some of them consider it as one of the last priorities. Unfortunately, sometimes the project manager tries to compensate for the delay in completing the project by reducing the surface preparation and paint application time, and orders for increasing the speed of the paint operations.
Paint is very important as the most common way to prevent corrosion. It also gives beauty to the facilities and will give the workers a sense of security and safety while doing their work. Lack of attention to the problems of paint leads to the rapid development of damage, especially in chemical and marine