Various types of stainless steel are increasingly widely and successfully used in a variety of marine environments. It must be pointed out that the long-term protection of stainless steel from corrosion in seawater requires complex anti-corrosion engineering technology and a lot of investment. Austenitic and martensitic stainless steels have long been used in superheater tubes and turbine blades on marine power plants. It is not easy to maintain low chloride levels in these installations, because the application technology of marine power plants is not different from the basic principles of ordinary power generation plants. Stainless steel is also being used in large-capacity chemical vessels on ocean-going merchant ships, and its use is in some ways very different from those used in land-based chemical plants.
Most stainless steel grades can be used with satisfactory results in marine conditions, but different grades are susceptible to stress corrosion cracking behavior. Martensitic steels represented by Type 410 and ferritic steels represented by Type 430 will rust within months under marine conditions. This uniform rust can be removed by mechanical grinding. The more popular stainless steels are austenitic stainless steels because of their resistance to rust (with the exception of stress corrosion cracking). along with
Over time, austenitic stainless steel will also turn black. If for aesthetic or other reasons, this blackening can also be removed by sanding. Stainless steel rarely produces uniform rust candles in seawater, so there is no need to worry about it in actual use.
Thrusters The thrusters on tugboats and other boats on the ocean can be made of cast stainless steel CF-8 (pretty dry type 304 stainless steel). When the ship is not sailing, a conductive metal loop is formed from the main shaft of the propeller through the bearing to the hull. Cast propellers equivalent to type 410 stainless steel are also often used, and are widely used in other areas such as icebreakers.
With the development of modern stainless steel technology, complex austenitic-ferritic stainless steel 20Cr-8Ni-3.5Mo has been used to cast large-scale propellers (up to 3000kg) on ocean-going ships.
Vessels that often work in ports are particularly prone to encountering logs or other floating bodies on the sea that can accelerate damage to the propellers. Therefore, the propeller made of austenitic stainless steel can be repaired by straightening or welding, which is a problem worthy of attention in material selection.
Pumps: Centrifugal pumps have long been observed to show some reliability in seawater operating conditions, such as stainless steel components. In the flowing seawater, using CF-8M cast stainless steel impeller (its composition is equivalent to 316 type stainless steel) and using 316 type stainless steel as the main shaft can be used without any problems. Crevice corrosion and pitting corrosion are likely to become serious problems when the pump stops working. But if you use more lively and rust-prone cast iron to make a
Cast iron can provide cathodic protection during downtime for pump boxes with considerable wall thicknesses. When the pump is working, the lower rust steel must be polarized under the cathodic protection of the cast iron box, but the flowing water maintains the cathodic protection. In addition, pumps that work for a long time may be protected by alternating use, sometimes replacing seawater with freshwater.
О-ring: Series electrical connectors and related О-ring locating devices are widely made of Type 304 and Type 316 stainless steel, especially in marine and military engineering. Satisfactory results can be obtained by using the above materials. O-ring seals can be cathodically protected by the hull, aluminum frame, or other factors. Without cathodic protection, the slack of the O-ring can quickly (some within a few weeks) produce crevice rot and cause serious failure.