Various types of stainless steel are increasingly widely used and successfully used in various marine environments. It is necessary to point out that the long-term corrosion resistance of stainless steel in seawater is subject to complex anti-corrosion engineering technology and substantial investment. Austenitic and martensitic stainless steel has long been used for marine power plant superheater pipe and a turbine blade. It is not easy to maintain a low chloride content in these devices, since the application of marine power plants is no different from the basic principles of general power plants. Stainless steel is also being used as a large capacity chemical vessel on ocean going ships, and its use is in some ways very different from the conditions of use of land chemical plants.
The results show that most stainless steel grades can be satisfied with the application in marine condition, but different grades are sensitive to stress corrosion cracking. The martensitic steel represented by type 410 and type 430 ferritic steel will rust in a few months in the ocean. This uniform corrosion can be removed by mechanical polishing. The most popular stainless steel is austenitic stainless steel, because of its strong resistance to corrosion (except for stress corrosion cracking). As time migration, austenitic stainless steel will be black. If the appearance or other aspects, the black can also through grinding to remove. Stainless steel will produce uniform corrosion rarely in seawater, so in actual use may not have to worry. The propeller on the ocean tugs and other ships on the propeller by casting stainless steel CF8 (a dry type 304 stainless steel). When a ship does not sail, it is made up of the propeller shaft through the bearing to the hull, forming a conductive metal circuit. Equivalent to the type 410 stainless steel casting propeller is often used, and in other areas are widely used, such as for icebreaker. The development of modern technology has begun to adopt stainless steel, Duplex Austenitic ferritic stainless steel 20Cr - 8Ni - 3.5Mo to cast a large propeller on the ocean liner (up to 3000kg). Ships often work in ports, especially when they are exposed to logs or other floating bodies on the surface of the sea. Therefore, the use of austenitic stainless steel can be produced by straightening or welding method of repair, which is a matter of attention should be paid attention to. Pump has been observed in the working conditions of the centrifugal pump in seawater, such as the use of stainless steel components, it can show a certain reliability. In the flow of water to maintain the use of CF - 8M casting stainless steel impeller (which is equivalent to the composition of 316 type stainless steel) and the use of type 316 stainless steel as the spindle, can not be any problem. When the pump stops working, crevice corrosion and pitting corrosion are likely to be a serious problem. However, if the use of a more active and easy to create a thick wall of iron oxide pump tank wall thickness, the cast iron in the downtime can play a role in cathodic protection. When the pump works, the cast iron box under the cathodic protection effect can make the rust steel polarization, but the flow of water to the role of the cathode protection.
In addition, the long-term work of the pump may be due to alternate use, sometimes replaced by fresh water into the sea and play a protective role. Bulk container stainless steel has been used as a container for bulk cargo containers for liquefied natural gas (LNG), chemicals, beverages, etc.. Container freight used by LNG Sheng type 304L stainless steel, its purpose is not to corrosion but considering the mechanical properties under low temperature. The purpose of the use of stainless steel containers for marine chemical products is to take into account its corrosion resistance, which is different from the storage and transportation of land chemicals. In the case of a vessel belonging to a general tramp ship, the vessel carrying the chemical can also carry any goods, from acetic acid, bad pulp to xylene. 316L type stainless steel is generally used for the valve, cargo pump, pipe, heating coil and the container itself. The container can be made of stainless steel or clad with carbon steel clad with a layer of 0.06 to 0.08in (1.5 - 2.0mm) stainless steel plate. Before use, it is necessary to conduct a careful inspection of the defects of the plate and conduct thorough cleaning and passivation. The experiment showed that the guest with the chemical allowed to flush with seawater, but then quickly washed with fresh water. For any stainless steel heating in a container device, when the previous chloride is not completely washed away and do not start to avoid stress corrosion cracking. Chemical containers should not be designed to be used to hold water because it can lead to the risk of crevice corrosion. If the design scheme is not used to fill the sea water, it is necessary to take into account the cathodic protection system to control the development of crevice corrosion. In this case, the stainless steel container may have to remove the calcareous sediments, this is a problem worthy of attention. Heat exchanger with forced water circulation system for steam condenser and cooler has been widely used in austenitic stainless steel pipe, the water inlet due to high pollution and should not be used for copper alloy material. Comparison of popular material for Type 316 stainless steel. In the coastal and harbor areas, a large number of foreign clumps and mud into the condenser pipe, particularly prone to serious obstacles, this situation must take measures to be excluded. A reasonable approach is to use a rubber ball circulating through the pipeline, because the rubber ball can be extruded to clean up the pipe wall. When the water flow velocity is about 1m / S, it can prevent marine organic debris is inhaled, so as to protect the pipeline from the condenser was produced corrosion. Different from other colored
