1 Introduction
Steel drums are packaging containers that contain and protect internal products. So the inner surface of the drum must be kept clean, ie there is no oil and any other contaminants. The rust inside the steel drum is iron oxide, which can contaminate the inner product. In the past, INSUNG has tested the following methods to control the rust in the barrel:
experiment method:
1) After welding, dry the weld with dry air.
2) Spray oil mist on the inner wall to prevent rust.
3) Spray oil mist to the weld area.
4) Change the traditional materials with nickel-plated cold coils.
Among these methods, the use of nickel-plated cold coils works best, so only this method has been used until now. The nickel-plated cold coil is coated with a thin layer of nickel particles on the surface of the cold coil. The speed of rusting is 2.5 to 3 times lower than that of ordinary steel plates. In spite of this, the high temperature zone created by the welding edge melts the nickel layer and causes rust from the surface. Therefore, a new method is to allow air and moisture to enter the interior of the barrel to prevent oxidation of the inner wall. This method uses dry air to replace the moist air inside the barrel, so that the humidity in the barrel contents is reduced, and the damp air inside the barrel is also reduced.
2. The principle of rusty steel drum
In general, the corrosion of most metals is related to moisture and oxygen in the air. The reaction between them causes a layer of metal oxides on the metal surface, which causes the metal surface to lose its luster. This process is rust.
The main component of rust is the hydrated oxide Fe2O3nH2O. This is the result of the reaction of the surface of the iron with water and oxygen. When iron is oxidized at high temperatures, a hard black scale surface is formed, which is another type of rust.
The chemical reaction of iron with water and oxygen produces oxides. The reaction equation is as follows:
Fe + 2H2O → Fe(OH)2 + H2
2Fe(OH)2 + 1/2O2 + H2O → 2Fe(OH)3
2Fe(OH)3 → Fe2O3 3H2O
3. Prevention of rust in barrels
To prevent the internal surface of the drum from rusting, it is necessary to prevent the inner wall of the drum from coming in contact with moisture and oxygen.
Use the following methods to prevent the internal surface of the drum from rusting:
1 Select anti-rust oil and quantity
The use of anti-rust oil will affect the coating quality on the surface of steel drums. If too much anti-rust oil is used, it will cause pollution in the barrel.
2 reduce the surface roughness of the steel drum
Reducing the surface roughness of steel drums will affect the paint adhesion on the drum surface, so reducing the surface roughness of steel drums is not the preferred method.
3 Treatment of Steel Drums with Zinc Phosphate
The use of zinc phosphate to chemically treat the interior surfaces of steel drums will cause pollution to the surrounding environment and produce industrial waste water. Therefore, this method is not allowed in Korea.
4 steel barrels with internal coating
The use of internal coating methods for steel drums increases production costs and may cause internal paints to react with the contents.
5 Avoid contact between steel drums and substances that can easily cause corrosion by steel drums, such as chlorine and sulfur.
The steel drum production line should be established in an environment where there is no possibility of causing corrosion of the steel drum. It is necessary to keep away from chlorine and sulfuric acid.
6 Limit the humidity of the air in the barrel
Studies have shown that reducing the humidity in the barrel air is the best way to reduce rust.
4. Method to reduce the internal humidity of the steel drum
Generally, to reduce the moisture in the barrel, the temperature and humidity of the air in the barrel must be reduced before plugging the lid of the drum. Prior to this, moisture was condensed by careful work.
1) Condensation of moisture
Change the amount of water vapor in the air. When the air temperature is low, the pressure will change, and the amount of water vapor will condense into liquid water when it reaches the minimum level.
Taking a closed barrel as an example, when the ambient temperature decreases, the water will condense, and the water vapor condenses into water in the barrel and causes the inner wall of the barrel to rust. In order to prevent the formation of water droplets in the barrel, there are two methods that can be used. One is to adjust the temperature of the outside so that a temperature difference occurs inside and outside the barrel to generate water droplets. Another method is to replace the wet air in the barrel with dry air or nitrogen or argon to reduce the formation of water droplets.
2) The effect of temperature inside the drum on rust
In general, when the air temperature is high, its humidity will be higher. If the air temperature decreases, the humidity in the air will decrease, and the moisture will condense and turn into liquid droplets.
After the outer surface of the drum is painted and dried, the temperature can reach as high as 120°C. Therefore, it must be cooled for a long time to make the inner temperature of the drum the same as the outside environment.
If the temperature of the air in the barrel is close to the ambient temperature in the same enclosure, the moisture in the barrel will decrease. Using this method (to cool the steel drum and allow it to cool gradually in line with the ambient temperature) can make the barrel rust later. Moreover, it must be stored until the drum is cooled, and it is best to use a cooling device to reduce the temperature of the painted drum surface.
3) Influence of moisture on the inner surface of the drum
In general, in South Korea, the maximum and minimum temperatures do not exceed 15°C during the day.
Assume that the drum volume is 200 liters, the internal pressure is atmospheric, the barrel temperature is 30°C, and the relative humidity is 90%. When the temperature decreases by 15°C, the amount of condensable water can be calculated by the following method.
In Table 1, saturated water vapor is 30.3g/at 30°C, and the amount of water vapor in the barrel is:
{30.3g/ × 0.2 × 0.90 (relative humidity) = 5.454g}
At 15°C, the saturated water vapor is 12.8g/, and the amount of water vapor in the tank is:
{12.8g/ × 0.2 × 1.00 = 2.56g}
Therefore, the amount of condensed water is:
5.454g ? 2.56g = 2.894g
This means that when the temperature in the barrel changes from 30°C to 15°C, 2.894g of saturated water vapor in the barrel is condensed to stay on the inner surface of the barrel. Therefore, to prevent rust in the barrel, 2.894g of water vapor must be condensed into liquid water and discharged outside the barrel.
Table 1. Saturated water vapor quantity (relative humidity: 100%, unit : g/)
temperature
Saturated steam
temperature
Saturated steam
temperature
Saturated steam
45°C
65.350
31°C
32.039
17°C
14.475
44°C
62.259
30°C
30.358
16°C
13.629
43°C
59.293
29°C
38.756
15°C
12.827
42°C
56.448
28°C
27.221
14°C
12.065
41°C
53.718
27°C
25.760
13°C
11.343
40°C
51.102
26°C
24.366
12°C
10.659
39°C
48.595
25°C
23.038
11°C
10.011
38°C
46.193
24°C
21.773
10°C
9.397
37°C
43.893
23°C
20.568
9°C
8.817
36°C
41.691
22°C
19.421
8°C
8.268
35°C
39.583
21°C
18.329
7°C
7.749
34°C
37.568
20°C
17.291
6°C
7.258
33°C
35.641
19°C
15.562
5°C
6.795
32°C
33.799
18°C
15.366
4°C
6.358
4) Urban Climate Conditions in Ulsan, South Korea
Table 2 and Figure 1 below show the urban climate conditions (including temperature, humidity, cleanliness, etc.) over the past decade in Ulsan, South Korea.
Table 2. The weather in Ulsan City, South Korea, for the past ten years.
January
February
March
April
May
June
July
August
September
October
November
December
Lowest temperature. (°C)
-2.7
-1.3
2.6
7.7
12.3
17.1
21.7
22.3
17.4
11.0
4.8
-0.7
Maximum temperature. (°C)
7.0
8.5
12.7
18.7
23.2
25.7
28.9
29.8
25.8
21.6
15.5
9.9
Average temperature. (°C)
1.6
3.2
7.4
13.1
17.6
21.1
25.0
25.7
21.2
15.9
9.6
4.0
Average humidity (°C)
54.7
56.0
61.6
64.6
68.2
76.6
80.5
79.7
77.2
70.0
64.0
56.8
Average cleanliness (°C)
-9
-7.2
-2.1
4.4
10.2
15.7
21.0
21.2
16.2
9.1
1.6
-6.3
Maximum temperature difference (°C)
9.7
9.8
10.1
11
10.9
8.6
7.2
12.4
14.8
16.8
16.2
7.2
Figure 1. Climate in Ten Years in Ulsan City, South Korea
According to this information, in the weather of Ulsan City, we can see that the average humidity and the average cleanliness are higher in the month where the average temperature is higher. Especially in the summer (July and August), the average cleanliness is similar to the minimum temperature, and the barrels are most likely to rust.
This means that containers such as drums are more likely to rust in summer months due to higher temperature and humidity.
5) Fill the drum with dry air to reduce moisture
(1) Dry air production
In Yingshan's production workshop in Ulsan, the production process of the dry air charged into the barrel is as follows:
Compressor→Gas tank→Filter→Air desiccant→Linear filter→Air tank→Dry air absorbent→Filter
First, the air is compressed by the compressor. Second, compressed air enters the gas tank. Third, dust and contaminants in compressed air are filtered through filters. Fourth, the moisture in the compressed air is liquefied by the freeze-dried agent. Fifth, the moisture in the compressed air is separated by a linear filter and the contaminants are filtered again before entering the gas tank. Sixth, the moisture and pollutants in the compressed air are again absorbed by the absorbent. Seventh, clean compressed air enters the steel drum through the filter.
(2) Experimental results of feeding dry air into the barrel
The experimental result of sending dry air into the barrel was the “dry air production line†at INSUNG in Ulsan. Referring to Table 3 and Figure 2, the indicators of dry air sent to the drum are: temperature 32°C, pressure 5kgf/cm2, input nozzle diameter 11mm.
Table 3. Experimental results of feeding dry air into the barrel
Sample number
Dry air before feeding
After dry air is fed in
200 liters
After dry air is fed in
400 liters
Air temperature
temperature
(°C)
humidity
(%)
Cleanliness
(°C)
temperature
(°C)
humidity
(%)
Cleanliness
(°C)
temperature
(°C)
humidity
(%)
Cleanliness
(°C)
maximum
(°C)
Minimal
(°C)
1
36.6
53.5
24.8
36.2
31.7
16.8
35.6
12.6
2.4
30.7
22.6
2
34.5
59.2
25.4
33
32.6
13.4
32.8
13.3
1.1
25.7
23.5
3
34.1
50.5
22.4
33
25.5
9.5
31.6
10.2
3.5
24.1
21.1
4
31.1
51.4
20
29.7
29.2
8.8
28
15
-1
24.6
14.9
5
30.9
61.4
22.6
29.5
29.5
8.9
29.2
12.3
-2.2
23.5
19.8
6
28
47.3
15.5
27.8
25
6.1
27.7
14.9
-1.2
25.3
12.1
7
twenty four
43
10
23.5
22.7
0.8
23.8
13.7
-6.1
19.9
7.4
8
22.6
56.9
13.6
20.6
35.2
5
21.6
14.9
-5.6
17.2
9.3
9
21.3
43.3
8.3
18.5
33.1
1.1
17.8
13
-10.4
11
3.6
10
19.4
52.5
9.5
19.3
19.9
-3.7
18.6
14.4
-8.2
11.3
2.5
Figure 2. Experimental results of feeding dry air into the barrel
Table 3 shows the changes in cleanliness and humidity in the barrel before and after 200 liters and 400 liters of dry air are fed into the barrel. When 400 liters of compressed air were fed into the barrel, the cleanliness in the barrel was 16°C lower than that of the barrel without compressed air.
Figure 2 shows the maximum temperature change in January, with a temperature difference of 8°C to 17°C (assuming that steel drums were used to hold chemical products in the month of the month when the temperature difference changed the most). At this time, the steel barrels that sent 400 liters of dry air to the barrel were left for a month without rust.
5 Conclusion
The above tests for preventing internal rust in steel drums are available. Another alternative is to replace the moist air with dry air, but the cleanliness is controlled within a reasonable range, which is effective for cost savings.
It has been two years since the INSURF company's dry air production system at the Ulsan plant has never complained about the rusting of steel drums in the past two years. They said that INSUNG's steel drums also made the quality of steel drums satisfactory during the rainy season.