- •Surface Preparation and Cleaning. Table of content
- •5.1.1.Hand tool cleaning.
- •6.5.1.2.Power tool cleaning.
- •6.5.2. Blast-cleaning.
- •Figure 6.2.
- •Illustration of various blasting methods
- •6.5.2.1.Centrifugal abrasive blast-cleaning
- •6.5.2.2.Compressed-air abrasive blast-cleaning.
- •Figure 6.3 Effect of nozzle pressure on cleaning rate
- •6.5.2.3.Vacuum or suction-head abrasive blast-cleaning.
- •6.5.2.4.Moisture-injection abrasive blast-cleaning (compressed-air moisture- injection abrasive blast-cleaning)
- •6.5.2.5.Wet abrasive blast-cleaning (Compressed-air wet abrasive blast-cleaning).
- •6.5.2.6. Other methods
- •6.6. Abrasives.
- •Table 6.1. Abrasive / Profile Comparative Chart
- •Table 6.2. How to specify Blasting
- •Table 6.3. Examples of production rates to a Sa 2 ½ condition.
- •Table 6.4
- •Table 6.5. Consumption rates at different Nozzle pressures.
- •6.6.1. Metallic abrasives.
- •Table 6.6.
- •6.7. Water jetting and hydro blasting
- •Figure 6.6 Rotating nozzles must be designed to fit the purpose
- •Figure 6.7 The water used must be free from impurities, which may contaminate the surface.
- •6.8. Electrolytic descaling with magnesium strips
- •Figure 6.8 Principle of electrolytic descaling
- •6.9. Preparation between paint coats
Table 6.2. How to specify Blasting
ISO 8501 |
SSPC |
NACE |
Description |
Sa 3 |
SP 5, White Metal Blast Cleaning |
1 |
Removal of all visible rust, mill scale, paint, and foreign matter by blast cleaning |
Sa 2 |
SP 6, Commercial Blast Cleaning |
3 |
Blast cleaning until at least 65% of surface is free of all visible residue |
Sa 1 |
SP 7, Brush-off Blast Cleaning |
4 |
Blast cleaning of all except tightly adhered residues of mill scale, rust, and coating |
Sa 2 ½ |
SP 10, Near-White Blast Cleaning |
2 |
Blast cleaning until at least 95 % of surface is free of all visible rust, mill. scale, paint and foreign matter. |
Table 6.3. Examples of production rates to a Sa 2 ½ condition.
(Newly fabricated steel using a 9.5 mm I.D. orifice nozzle at 7 bar)
Abrasive |
Abrasive Consumption |
Production Rate |
Comments |
Silica sand 16/40 mesh |
12.7 kg/m2 |
26 m2/hr |
35 micron profile; dusty |
Crushed flint 12/30 mesh |
17.6 kg/m2 |
15 m2/hr |
75 micron profile |
Staurolite 50/100 mesh |
15.1 kg/m2 |
27 m2/hr |
10-15 micron profile; smooth surface |
Coal slag 16/40 mesh |
15.1 kg/m2 |
21 m2/hr |
60-70 micron profile |
Copper slag 16/40 mesh |
15.1 kg/m2 |
24 m2/hr |
50 micron profile |
Garnet 36 grit * |
17.6 kg/m2 |
20 m2/hr |
35 micron profile; very little dust |
Aluminium oxide 36 grit * |
15.1 kg/m2 |
25 m2/hr |
35 micron profile; very little dust |
G-40 steel grit * |
26.8 kg/m2 |
17 m2/hr |
60-70 micron profile; no dust |
*) These abrasives can be re-used.
Table 6.4
Examples of cleaning production rates to different blast cleaning standards.
(For a three-person crew day on lightly rusted steel,
using 30/40 mesh medium hardness abrasive. 9.5 mm orifice nozzle at 5.6 bar)
Method |
Production Rate |
Abrasive Used |
Sa 3 |
90 m2 |
4500 kg |
Sa 2 |
230 m2 |
3600 kg |
Sa 1 |
480 m2 |
3000 kg |
Sa 2 ½ |
140 m2 |
5600 kg |
Table 6.5. Consumption rates at different Nozzle pressures.
Orifice Size |
4.2 bar |
4.9 bar |
5.6 bar |
6.3 bar |
7.0 bar |
|
5 mm |
0.84 77.5 7 |
0.92 89 7.5 |
1.06 98 8.5 |
1.15 108 9.5 |
1.26 120 10 |
Air (m3/min) Sand (kg/h) HP* |
6.5 mm |
1.51 141 12 |
1.71 160 13.5 |
1.9 185 15 |
2.08 203 16.5 |
2.27 224 18 |
Air Sand HP |
8 mm |
2.5 242 20 |
2.83 274 22.5 |
3.16 304 25.5 |
3.53 335 28 |
3.84 368 30.5 |
Air Sand HP |
9.5 mm |
3.53 346 28 |
4 391 32 |
4.5 435 36 |
4.85 477 38.5 |
5.5 522 44 |
Air Sand HP |
11 mm |
4.76 467 38 |
5.44 533 43.5 |
6.09 594 48.5 |
6.73 656 53.5 |
7.11 718 56.5 |
Air Sand HP |
12.5 mm |
6.28 605 50 |
7.06 685 56 |
7.85 761 62.5 |
8.65 841 69 |
9.46 917 75 |
Air Sand HP |
16 mm |
9.95 969 80 |
11.3 1097 90 |
12.6 1218 100 |
14.1 1347 112 |
15.35 1472 122 |
Air Sand HP |
19 mm |
14.1 1384 112 |
16 1566 127 |
18 1740 143 |
19.4 1906 154 |
21.95 2087 175 |
Air Sand HP |
*) Electric motor horsepower required to produce indicated cubic metres per minute.