Faculty of Engineering, Universiti Malaysia Sabah, Sabah, Malaysia
Received Date: January 23, 2017; Accepted Date: March 14, 2017; Published Date: March 24, 2017
Citation: Shah MMK, Ismail A, Sarifudin J (2017) Investigation of Effect on Prefabricated Light Steel Structure Non-coating and Coating Using Transogard Zinc Chromate Paint after Exposed to Seawater. J Material Sci Eng 6: 326. doi: 10.4172/2169-0022.1000326
Copyright: © 2017 Shah MMK, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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The main objective of this research is to determine corrosion rate and weight loss for the coated and non-coated with several layer of mild steel AISI 1020. This research discussed and focusing on prefabricated material coating and non- coating of light steel structure effect on seawater and study on the research have been done before by others researcher for better understanding on this research. Basically, most of the researches conducted before are only focusing on the type of prefabricated materials. However, in this research the coating will be used in other to improve the properties of materials.
AISI 1020; Coating; Optical microscope; Zinc chromate; ZnCrO4
This research is conducted due to the problems faced by the marine area. Firstly, there is no specific coating can be used to coat the light steel for the application in sea water, the right selection for light steel material should be done properly for better outcome of experimental result without neglecting the cost [1-3].
The following objective need to achieve:
• To investigate the profile of prefabricated material light steel coated and non- coated structure after exposed to sea water.
• To determine weight loss of the coated and non- coated light steel material due to sea water.
The coatings based in chromium (VI) already used since a long time ago and now prohibited because of the toxic content especially chromium (VI) [4-6]. A solution came out, which is trivalent chromate coating, but this coat does not produce the yellow color like the hexavalent chrome coating does. But the function is quite same as the hexavalent chrome coating, so it is used to replace hexavalent chrome in coating, since trivalent chromate coating is more environmental friendly [7-10].
“Many factors in surface preparation affect the integrity of coating which includes residues of oil grease, rust on the surface and mill scale which can decrease adhesion or mechanical bonding of coating to the surface” . Coating is mostly used in Steel piling and other maritime structures because coating constitute the most commonly used and most effective method of corrosion control of marine structures.
The coating used in this experiment will be transogard zinc chromate Paint. The chromate type used is trivalent chromate coating which is a non- toxic paint. The paint Chemical formula is ZnCrO4 and the appearance of the coating is yellow- green crystals (Figure 1).
This is shows that before applying any kind of coatings the penetration playing an important roles in order to make sure the coating fully covered the specimen surface. Besides that, the surface finishing also important to make sure the coating fully used as the protective surface to minimize the corrosion occurs. In seawater, the reduction of dissolved oxygen molecules is the primary cathode reaction on the specimen surface, and such a steady current is due to the limitation of oxygen diffusion. Based on the result also shows, the corrosion rate of the coating depended on its porosity.
The weight loss is converted to a corrosion rate (CR) or a metal loss (ML), as follows:
The constant used, k coefficient is 3.45 × 106, the desired corrosion rate unit used is Mils/ year (mpy) and the area units used is in cm2. The density used is 7.87 g/cc @ g/cm3
The specimen used will be in rectangular design, before the experiment conducted, preparation of the specimen is the complex system (Figure 2).
Surface finishing methods vary across a broad range for better result. Type of steel used is AISI 1020 in the experiment. Firstly, cut the material into rectangular design with size 3 mm × 30 mm × 80 mm. Clean of specimens before weighing to remove any contaminants that could affect test results. The specimens clean by using grinding and polished using sand paper (Figure 3). Before coat the specimen, the samples will be degreased with ethanol and labeling to easier to identify the specimens (Figure 4).
After the cleaning process, 12 pieces of mild steel rectangular design will be coated with one layer of Zinc chromate, ZnCrO4 paint with the thickness of 0.09692 mm. 12 pieces of mild steel rectangular design will be coated with two layer using the same paint which are Zinc chromate, ZnCrO4 with the thickness of 0.14792 mm. the second layer applied when the first layer is completely dry. The other 12 pieces will be in non- coated condition.
The digital scale weigh will be used in order to weigh the specimen, before and after the experiment or test conducted (Figure 5).
A closer picture of the corrosion products formed after progressive corrosion for long-term atmospheric exposure and compared to neutral salt fog and ASST accelerated methods is shown in Figure 5. The progressive corrosion product formation follows the same pattern as during initial corrosion, as described in the preceding paragraph for each corrosion exposure type . From the figure above it is showed that how we can examine the corrosion happened effect of exposed to seawater (Figure 6).
Optical microscopy without coating
The reddish colour covered most of the surface and the red participate more thick than 10th day, 20th day and 30th day. The based with silver and white colour show the area of the metal without any coating (Figure 7) [13-15].
Optical microscopy with one layer of coating
The size of water bubble on the paint layer is decreases compare to the 10th, 20th and 30th days. Besides that, the number of the bubble produce after submerged into the water is decreases covered the surrounding of the specimen surface but some of reddish colour is form on the surface (Figure 8).
Optical microscopy with two layer of coating
“Many factors in surface preparation affect the integrity of coating which includes residues of oil grease, rust on the surface and mill scale which can decrease adhesion or mechanical bonding of coating to the surface”. This shows; the coating cannot be function fully as protective to the surface because of surface preparation (Figure 9). The mechanical bonding of coating to the surface also plays an important role, to avoid the bubble to form between the coating paint and the mild steel. Hence, effect of the bonding between the coating paint and the mild steel is not strong to prevent the corrosion process of mild steel during exposed to sea water [16,17]. Thus, the water bubble is form, the corrosive sea water inside the bubbles do the corrosion process (Tables 1 and 2).
|Days||Condition||Initial Weight(g)||Final Weight(g)||Weight loss(g)||Surface Area(cm2)||Corrosion rate(mmY)||Percentage of weight loss (%)|
|One -layer coating||134.9469||135.1761||-0.2292||5.43548||-77.02||-0.1698|
|One -layer coating||136.0834||136.1232||-0.0397||5.44794||-6.655||-0.0292|
|One -layer coating||134.4546||134.4814||-0.0267||5.429353||-2.99||-0.0199|
|One -layer coating||143.9855||143.9846||0.0009||5.511080||0.07||0.0006|
Table 1: Corrosion rate.
|CR||Corrosion Rate||1Mils/year (mpy)|
|k||coefficient||3.45 × 106|
Table 2: Units properties.
The samples without coating showed increment in percentage of weight loss as the time increases. The percentage of weight loss increase directly proportional with time when the specimens exposed to sea water without any protective layer to reduced corrosion process (Figure 10). The specimens applied with one layer of coating, the percentage weight loss during the 10th, 20th and 30th day is negative. This is means when the percentage of weight loss is negative there is no weight loss occur, the specimens gain weight due to the layer of the coating produce bubble and stored water inside the specimens surface through bubbles. On the 40th day, the percentage of weight loss is 0.0006%. This is shows the corrosion start to take place at the 40th day. For the two layer of coating the percentage weight loss is negative along the period [18-21].
While the rate of corrosion, of the samples without coating showed decrement in corrosion rate as the time increases. The Corrosion rate decreases as the time increases, but start to increases on the 40th day. The specimens applied with one layer of coating, the percentage weight loss is negative on the 10th, 20th and 30th day. This is means when the percentage of weight loss is negative there is no weight loss occur, the specimens gain weight due to the layer of the coating produce bubble and stored water inside the specimens surface through bubbles [22,23]. On the 40th day, the corrosion rate is increases to 0.07mmy. This is shows the corrosion start to take place at the 40th day. The corrosion rate is slowly increases after undergoes the highest increment in corrosion rate due to the corrosion rate approaching the positive corrosion rate. For the two layer of coating, the corrosion rate is negative along the experiment period of time. The specimens start to undergo the corrosion rate after approaching the positive corrosion rate (Figure 11).
The corrosion take place after the water bubbles is formed. This is because the corrosion occurs between mild steel and sea water and the increases the weight loss of the samples. The surface finishing is also some of causes to the water bubbles to forms [24,25].
The data that was recorded show that there are different outcome from different condition of specimens surface. It is showed that with some protection of the mild steel surface can reduce the weight loss and also reduce corrosion rate. In addition, the water bubbles produce is due to the bonding attraction between the water and the mild still is high compare to the bonding attraction between the paint coatings and the mild steel. This is because the corrosion processes occur due to the presence of some ion presence on the mild steel and sea water. The coating only acts as to reduce the corrosion rate.
We would like to take this opportunity to express our deepest appreciation and gratitude to those people who had guided and assisted us doing this research. We thank our colleagues from University of Malaysia Sabah who provided insight and expertise that greatly assisted the research, although any errors are our own and should not tarnish the reputations of these esteemed University of Malaysia.