Avoid metal corrosion failure

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Seaside areas are often faced with harsh conditions due to the high levels of salt content Corrosion problems.

Whether the area is close to seawater, it is often sprayed with sea water
Splashing, or occasionally by the turbulent tide, rapid corrosion of materials are phase
When worrying about the problem. Immediately adjacent to the sea buildings, railings, lamp posts, carvings
The plastic faces the risk of corrosion including premature visual impairment and complete structure
Failure and so on.
Experts studying atmospheric corrosion have thoroughly studied the rot of coastal areas
Erosion factors, but designers usually do not understand these studies, or
Do not know how to apply the research results in the design project. In addition, off
Corrosion behavior of the material and how far sea salt drifts from the shoreline
Land and other aspects there are still some wrong ideas. This article helps designers
Judge the corrosion of coastal areas, and use cases to illustrate the relevant materials
performance.

What factors will affect the corrosion?
Corrosion occurs under the condition that the surface of the material must be made of the electrolyte
Wet, electrolyte is a conductive aqueous solution. Material surface is regular
There is a direct correlation between wetting and its rate of corrosion, and salt
Will increase the conductivity of water and accelerate the process of corrosion, salt can destroy some
Protective oxide formed on metal surface. For example, regular exposure to
Salty environments destroy the protective coating of metallic aluminum.
The moisture that is necessary to cause corrosion can come from rain, fog or even
Water vapor in the air (humidity). Heavy rain or thunderstorms can help remove the potential
In the harmful sediments, but the salt content of light rain will instead be due to moisture
Increased gas and salt content exacerbate corrosion. Shown in Table 1 Pro
Under combination of humidity and temperature, salts on the surface of the material begin to absorb water
Points and forms a corrosive chloride electrolyte solution. The weather in one area
The situation data helps to determine how often salt is activated by temperature and humidity conditions,
Presence of salt fog and coastal forms of rainfall.
Table 1 sea salt and deicing salt began to absorb water to form a corrosive chloride solution
Temperature and humidity levels

Salt absorption of water to extend the corrosion time, increase the pollution
Corrosiveness of dyestuffs and particulates. Rough surfaces cause higher corrosion
Rate because the rough surface accumulates more corrosive surface deposits and makes
Moisture stay for a long time. So, in the coastal corrosive environment, the best
The use of a smooth surface material designed to facilitate the rain washed, and / or system
Set manual cleaning program.
When the building is very close to the brine, the building is slightly higher
And the parts directly affected by the sea breeze the highest corrosion rate. To illustrate the high

The impact of the degree, the carbon steel sample placed in Canavell, Florida
Cape Coast 55 meters (180 feet). Samples are on the ground and 18 meters from the ground
The annual corrosion rates at (60 ft) high are 0.131 and 0.165 mm (5.2
And 6.48 mils), while corroded at 9 meters (30 feet) from the ground
Rate 3 times higher than the ground (0.44 mm / 17.37 mils) 1,2. Corrosion occurs
The height of the most serious parts, along with the shape of the coastline, wind speed and ground and
Water temperature varies.
Sea salt environment
Sea salt (including sodium chloride, calcium chloride and chlorine) is applied when the waves reach the coast
Magnesium) becomes suspended particles floating in the air. Salt concentration in the sea air
Many factors depend on the wind speed, the turbulence of waves, and the tortuous course of the coastline
Degrees and the temperature difference between land and sea. Weather conditions and surf situations often
Every month is changing, the salt content has obvious seasonal differences.
The distance the salt migrates inland is determined by the weather, geographical conditions and water droplets

Size and initial concentration of suspended salt particles and other factors. In some places
Side, sea salt is limited to about 1.6 km (1 mile) from the beach,
In other places, 48 ​​km (30 miles) away from the sea
Inland there is also a fairly high salt content 2,3.
Panels A and B are the United States National Atmosphere Deposition Project Group (NADP) 4
Chloride (salt) deposition data collected between 1994 and 2006. The figure
It shows how salt deposition changes with time and climate.
From the map you can clearly see the coastal areas of California and the Atlantic Ocean
Central Coast salt content is different. Other countries have also drawn similar chlorination
Sediment maps, which are an important tool for assessing the corrosivity of coastal areas.
If you can find such a corrosion map, understand the chlorine in a region over the years
Concentration and pollution, acid rain and weather conditions can be helpful.
When the waves impact the coast, they form suspended salt particles and the corrosion rate will increase.
The height and direction of the waves, the width of the waves, the base of the waves, extend into the sea
Terrestrial, coastal and cliffs will affect the content of particulate matter. Sea relative
Quiet areas (such as safe haven or estuary), salt content is less 5.

The most corrosive coastal areas in the world vary greatly in appearance,
include:
Part of the coasts of the Middle East and Australia (high temperature, high local humidity,
Little rainfall);
New Scotland, Canada (high concentrations of salt spray and small regular
rain);
· Rocky or surging coastline from South Africa to Hawaii.
Research shows that the area with the highest corrosion rate is generally 400 away from the coastline
To 600 meters (1300 to 2000 feet) and to the last 50 from the coastline
At 200 meters (165 to 650 feet) 3, corrosion rates have increased exponentially
plus. Generally more corrosive in the coastline or beyond the coastline,
Because there is a tidal wave splashing.
For often soaked in salt water (or salt water) or subjected to salt water splash
Use, the choice of materials need to follow the recommendations of the corrosion experts should be taken
Designed for use in immersion in salt water designed metal, such as “sea
Water-grade “stainless steel (super ferritic stainless steel, super duplex stainless steel, or
Super austenitic stainless steel). Note: 316 stainless steel is not sea level not
Stainless steel, not suitable for complete immersion in seawater or often subject to seawater fly
Splashing uses. In addition, some corrosion control methods can be used to extend the corrosion resistance
Erosion life of materials with poorer properties, however, the service life is still limited
It also needs regular inspection.

“Metal choice”
For architectural applications, the material does not even perforate or
Structural damage, whose appearance declines over time, is also considered
Is a failure. If aluminum, zinc and carbon steel (anode metal) are not and inert
Larger metals such as stainless steel and copper are carefully separated by galvanic corrosion
Greatly accelerate the corrosion rate of the anode metal. The right picture has a galvanized steel bolt,
316 stainless steel ladder used to fix the dock on the pier, galvanized steel bolts
Corrosion is taking place at a higher rate of corrosion and the failure of the bolt will result in the original failure
The damaged ladder collapsed. In salt-containing environments, in addition to corrosion resistance
The strongest stainless steel, all of the metals mentioned in this article are prone to crevice corrosion
Erosion (ie corrosion at tight junctions), joints must be sealed
Prevent it from premature failure.
Galvanized steel bolts to attach 316 stainless steel ladders and trestles with high corrosion rates
Corrosion occurs. Failure of the bolt will cause the originally undamaged ladder to fail in service.

“Stainless steel”
Because stainless steel is the best corrosion resistance, the most inhuman architectural gold
Genus, often used in corrosive coastal areas, so galvanic corrosion to stainless
Steel is not a problem. Stainless steel has many different kinds of them
Has its own different corrosion resistance and strength. The most widely used
304 stainless steel, due to surface rust, usually not used for beach use,
Even so, the corrosion rate of stainless steel is also commonly used in building aluminum alloy
1/10 to 1/1006, 7 of the material. It happens even though the surface of it is corroded
Structural failure and perforation also take hundreds of years.
316 stainless steel with smooth surface and stronger corrosion resistance is coastal
District most commonly used stainless steel grades. If the building structure is infrequent or regularly
By the splash of salt water, or if the content of suspended salt particles is particularly high,
Can consider more corrosion-resistant stainless steel such as 2205, 904L and
317LMIN. Often use duplex stainless steel such as 2205 to reduce the high intensity
Widget section size reduces costs.
Progreso, Mexico Two adjacent
Trestle Pier, showing stainless steel and
Differences in long-term performance of carbon steel. Right back to
The pier still in use was built in 1941
Year, using stainless steel reinforcement, soil
Core sample shows no stainless steel or structure
There is damage. Beside it has been completely damaged
The pier was made of carbon steel in 1960
Built of tendons

“Aluminum alloy”
For the common aluminum alloy construction materials, the salt environment is destroyed
The most serious environment. Although the distance will be different, but in general, in the distance
Within 0.8 km (0.5 miles) from the sea, the corrosion of aluminum alloy is the most serious. in case
There are also sulfur dioxide or acid rain in the environment, the corrosion rate will be significantly increased. Such as
Fruit inland at least 3 to 8 kilometers (2 to 5 miles) from the shoreline
With aluminum, sea salt, the corrosion of aluminum is usually greatly reduced. Even more
Used near inland, it is also often necessary to use anodized aluminum or watch
Apply a protective coating to the surface and require regular maintenance cleaning so that
Keep the original smooth surface 8.
In salt-containing environments, aluminum is most easily oxidized except zinc
Construction metal. Care must therefore be taken to separate the metal to avoid rapid corrosion
Failure. Certain grades of 2xxx and 7xxx aluminum alloys are highly crystalline
Corrosion, delamination or stress corrosion cracking should not be used
Coastal environment. Structural aluminum can be produced as a result of surface corrosion in coastal environments
Raw fatigue failure, should be better corrosion resistance, high strength aluminum alloy. When one
A higher salt content, the material should consult the views of experts.

“Copper”
There are many types of copper alloys, some often used in salt water environment. high
Purity copper alloys are often used for roofing and other architectural purposes. Corrosion of copper
As low as aluminum, up to 10 times higher than aluminum. Copper corrosion is generally considered
Aesthetically beautiful (unlike stainless steel and aluminum). Copper in the sea
Corrosion rates vary greatly in the environment, in the most corrosive environments
Piercing can occur on the roof in less than 50 years. Galvanic corrosion of copper in general
not a problem. If you want to use copper in ecologically fragile coastal areas, you have to
Be cautious because copper is a potential biocide.

“Carbon steel”

Exposed carbon and weathering steels are very fast in high-salt environments
Raw corrosion. Weathering steels will not form in high-salt or high-sulfur dioxide environments
The protective oxide layer has a corrosion rate similar to unprotected carbon steel. bare
The corrosion rate of exposed carbon steel is 100 times higher than that of aluminum and 8000 higher than that of 316 stainless steel
Many times. In addition, because carbon steel is more lively than stainless steel or copper, it must be put
Carbon steel and 316 stainless steel or copper carefully separated.
Protective coatings and / or multi-coatings containing zinc and aluminum (zinc) may be used
System to extend the service life of carbon steel in the coastal areas. The regular dimension of the coating
Protection is essential. Once the coating peels off, corrosion will accelerate. Metal coating
The service life of the layers varies significantly with the severity of the environment. in
In some places, red rust was seen in less than three years, while others were there
Corrosion occurred more than 20 years ago. In the most demanding coastal environment, in general
Metal coating plus multi-layer coating to extend the service life. Even if taken
These precautions, carbonated steel fences in the splash zone, can only last up to 8 years
Without structural damage. Zinc is a potential biocide, and sometimes it is needed
To collect and purify runoff water from zinc alloy and galvanized roofing.

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