Corrosion Control & Protection – Part 2
Display Surface
Surface profile is determined by a number of variables that are determined as follows: —
1. Strength and hardness of the surface cleaned
2. The speed of the abrasive
3. The hardness and density of the abrasive
4. The size or mass of the abrasive
5. The angle of the abrasive action
6. The particles of the abrasive
7. The time when the surface is exposed to radiation
What is Hydro-rays?
A purification technique is basedthe energy of water striking a surface in order to achieve its purifying effect.
Two different operating pressures are commonly used:
1. High pressure water blasting to operate at pressures above 680 bar (10,000 psi)
2. Ultra-high pressure hydro-blasting operation at pressures above 1700 bar (25,000 psi)
What is water cleaned?
1. Low pressure water washing works with pressure of less than 68 bar (1000 psi)
2. High pressure water wash is working at a pressure between 68-680bar (1000-10,000 psi)
3. Radiation uses high-pressure hydraulic pressures between 680-1700 bar
(10,000-25,000 psi)
4. Ultra-high pressure hydro-blasting works with pressure above 1700 bar (25,000 psi)
typically in the range 2000-2500 bar (30,000-36,000 psi)
Benefits of Hydro-rays on chemical blast cleaning
1. Health and Safety
Uses no abrasive, reduces the risk of injury
No breathing problems for the operators of dust
Reduced noise levels
No sparkProduction
Minimal disruption to other work in the vicinity
2. Contamination
No ingress of dust on wet paint, delicate machine parts
No clean-up requirements
3. Surface salt reduction
Reduce salinity at the surface
Soluble salt contamination
Salt contamination of steel and other substrates in the ballast water of ships and tanks is a common cause of breakdown of the coating blistering. There are two known mechanisms for development of blisters, osmosis andCorrosion.
If the surface is contaminated with hygroscopic material prior to painting for more than a critical mass, then osmotic blister failure is likely to occur in operation. Hygroscopic materials such as salts contained in sea water tend to absorb water. Pull the water through the coating, where the volume forces blistering. This type of error often occurs within weeks of immersion. The critical mass depends on a number of factors, including coatingCharacteristics and environmental factors. The more soluble salts, the greater impact. Sodium chloride is more soluble than sodium sulfate, and is therefore a harmful impurity.
Breakdown by corrosion is a gradual process, but should appear as a rule for many months. The presence of electrolytes under the film promotes the corrosion. The corrosion products generated at the cathode to have a strong osmotic effect, causing blisters, while the anodeproduced voluminous rust, caused blisters.
Be the source of the contamination salts in ballast and cargo tanks from previous cargoes, ballast water, the atmosphere, wash water and also from abrasives used to prepare the steel. Many shipowners are indicating salt contamination in their new plating and construction services.
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