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The use of stainless steel in marine environment

DataTime:[3/13/2017]

Stainless steel has been successfully and widely used in a variety of marine environments, because in order to stainless steel in the seawater environment long-term corrosion resistance, the need for a very complex stainless steel processing technology. Austenitic stainless steels, martensitic stainless steels have long been used in the manufacture of navigational power units on superheater pipes and turbine blades.

 

In addition, these stainless steels are also used to make large-capacity chemical containers on ocean-going vessels, and the use of these devices is sometimes different from the conditions used by the land chemical plant.

 

Many grades of stainless steel can be used very well in marine environments, but different grades are sensitive to stress corrosion cracking. Martensitic stainless steel on behalf of 410 and ferrite stainless steel on behalf of 430, if in the marine environment, a few months time will rust. However, such uniform rust can be removed by mechanical grinding.

 

The more popular stainless steel is austenitic stainless steel because the steel is more resistant to corrosion. But the time is too long, the same will be black. Also can be polished to remove these blacks. And the steel stainless steel in the water generally do not occur evenly rust, so do not worry too much.

Stainless steel leaves

Stainless steel leaves

 

The use of stainless steel in marine environment

 

The stainless steel components in the propeller

 

The marine vessel's propeller can be made of cast stainless steel CF-8 (similar to 304 stainless steel). When the vessel stops sailing, from the propeller spindle through the bearing to the hull, constitute a conductive metal circuit. Cast stainless steel, similar to the chemical composition of 410 stainless steel, is also often selected as a propeller, and is also widely used in icebreakers.

 

With the development of stainless steel technology, also has a compound austenitic - ferritic stainless steel 20Cr-8Ni-3.5Mo to cast large-scale propeller on the ocean wheel (weight 3000kg).

 

Often in the port operations of the vessel, the propeller is vulnerable to the impact of debris on the sea and accelerated damage. So the austenitic stainless steel as raw material made of the propeller can be straightened or welded way to repair, so the material is to consider this aspect.

 

Stainless steel components in the pump

 

When the centrifugal pump operating environment is the ocean, such as the pump has a stainless steel components, equipment, the reliability will be significantly increased. Seawater CF-8M cast stainless steel impeller (similar to 316 stainless steel) and 316 stainless steel as the spindle, the reliability is very good. If the pump does not work, it is likely to be crevice corrosion and point corrosion. So you can use a more lively and rusty cast iron to make a considerable wall thickness of the pump, so cast iron in the downtime will have a cathodic protection of the pump. When the pump work, the cast iron box under the protection of the cathode will be able to make the next rust steel, but the flow of water to be cathodic protection. In addition to long-term work of the pump is best for seawater and fresh water, the use of different equipment.

 

Bulk containers

 

Stainless steel is also often made of bulk containers, such as liquefied natural gas (LNG), chemicals, beverages and so on. Generally use 304L stainless steel to make the shipment of LNG containers loaded, the purpose is not to corrosion but to pay attention to the low temperature of the stainless steel mechanical properties.

 

The containers of marine chemicals generally take into account the corrosion resistance of stainless steel, which is contrary to the storage and transportation of terrestrial chemicals. If the vessel is an ordinary non-scheduled freighter, the container carrying the chemical can also carry other items such as acetic acid, bad pulp or xylene. Usually 316L stainless steel as raw material to make the valve, cargo pump, tube, heating coil and the container itself. The container can be made of stainless steel or made of carbon steel in a 0.06-0.08in (1.5-2.0mm) stainless steel plate. However, before use, be sure to carefully check the container stainless steel plate is defective and thorough cleaning and passivation treatment.

 

Stainless steel components in heat exchangers

 

Austenitic stainless steel pipes are now widely used in forced water circulation systems for coolers and power plant steam condensers, which are not suitable for use with copper alloy because of their high levels of contamination. 316 stainless steel is more appropriate to use. In the coastal and harbor areas, a large number of foreign agglomerates and sludge into the condenser pipe, very prone to serious obstacles, then we must take measures to exclude. A reasonable measure is to use a rubber ball to circulate through the pipe, because the rubber ball can produce squeeze to clean up the pipe wall. When the flow rate of seawater is about 1m / s, it can effectively prevent the inhalation of marine organic debris, so that the condenser pipe can not produce point corrosion. Unlike other alloys, the condenser duct made of stainless steel is not limited by the maximum flow rate but is related to the economic effect of the entire pump unit.

 

O-ring

 

Series-type electrical connectors and associated O-ring positioning devices are usually made of 304 or 316 stainless steel, especially marine and military engineering. This effect is very good. O-shaped seal can be through the hull, aluminum frame to be some factors to obtain cathodic protection. But once there is no cathodic protection, the O-ring is so bad (or even weeks) that it will lose its function because of crevice corrosion.

 

Source: Yaang Pipe Industry Co., Limited (www.yaang.com)

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