Application of Stainless Steel
Stainless steel not only has good corrosion resistance but also has various characteristics such as a good appearance. The application range of stainless steel is becoming more and more extensive. The following table is a simple example of the application of stainless steel:
1. The application of stainless steel in the construction industry
In recent years, the use of stainless steel as a building material has become increasingly widespread. There are many reasons for its increasing use, including a better understanding of materials, attempts to update certain designs, and the idea of producing a structural material that is both durable and maintenance-free.
In the early days, the use of stainless steel in construction was limited to certain occasions. In the past, architects were looking for a new material with special effects when it was thought that there was no suitable material. In fact, on many such occasions, stainless steel has been used for a long time and its effect has been continuously scouring the stainless steel for a long time, making manufacturers believe that stainless steel materials used in outdoor occasions will not corrode even under highly corrosive gas conditions.
Because stainless steel has two characteristics of durability and almost no need to maintain the surface, it makes people pay more attention to its application than ever before. The prices of most building materials have risen rapidly at a certain percentage, and the prices of many materials have risen far more than stainless steel materials. The cost of maintaining and maintaining the building’s internal and external structures in good condition has increased dramatically. Today’s architects must seriously consider the entire situation of the building. If the building needs to be replaced or repaired for many years, then the architect’s design is a failure.
In recent years, the walls of swimming pools have been made of stainless steel. Concrete, the main material used for a long time, needs to be repaired and painted every year, especially in the northern regions. Swimming pools built with carbon steel and coated also need a large area of scrubbing and painting every year, both of which add to the swimming pool. Considerable usage expenses.
When the swimming pool is made of stainless steel (Type 304, 2B finish) as the sidewall, scrubbing is very simple, and it can be washed quickly with water and soap. Nowadays swimming pools often use stainless steel tank walls and concrete bottoms, and the bottoms are made of concrete for anti-skid.
The walls of some buildings use Type 304, Grade 8 mirror polished stainless steel as the material.
The interconnected stainless steel plates have been polished and colored to make the walls have uniform color and reflectivity. In order to prevent grease stains, the exposed part of the large-area stainless steel plate (fluff feet) is installed in a thick interlayer composed of a galvanized plate and a compressed plate. The polished stainless steel plate is connected and fixed with the galvanized steel plate with epoxy resin as an adhesive.
Dry stainless steel can get very soft properties, making it possible to be used as a roof covering material. It is precise because this material is easy to form, durable and beautiful, many architects choose stainless steel not only as a protective layer but as an integral part of the overall design.
Some buildings (indoor skating rink tubes) use stainless steel to build the Yongping overlapped roof, which not only makes the building beautiful from the design point of view but also makes the indoor skating season prolonged due to the reflective effect of the stainless steel surface. Undertake unreasonable investment.
For some special structures, many problems are often solved due to the application of stainless steel. For example, there is a garage. The design requires that the garage not only protects the parked cars but also has good ventilation for the exhaust gas; at the same time, it can also allow a certain degree of sunlight to enter the garage. The selection of materials is durable and requires no maintenance.
In order to meet the above requirements, the designer chooses 6*10in (15*25cm) 201 stainless steel grating, and fixes the grating on the vertical column, so that the inside and the outside are staggered to create an overlapping layout. In order to enhance the architectural design effect, staggered outer grating The upper surface adopts a floating surface finish, the outer row of column grids adopts an ordinary 2B finish, and all the inner grids are 2D finish. This changing pattern of lending gives the garage a vivid appearance.
For the roof structure of a building, its service life and appearance should be equally valued. In the airport restaurant, in order to make the roof beautiful, the exhaust fans are covered with stainless steel plates. When choosing a covering material, the non-reflective properties of the material are also particularly emphasized. The selected village material is type 304 stainless steel, rough polished, low reflectivity, and grade 6 finish. Special attention should be paid to the choice of brightness, especially due to glare, which hinders the pilot’s sight when landing at the destination.
Stainless steel is used in the interior and exterior building structures of the office lobby. Its construction measures use stainless steel as the curtain wall. The columns at the entrance of the building are covered with stainless steel plates, and the purification devices of all windows on the front of the building are covered with stainless steel.
The non-flowered board above the restroom of the office building is composed of stainless steel plates with embossments. Use male and female dies to punch the embossed part of the stainless steel sheet.
Stainless steel not only has a long service life but is also a good material for making convex structures. This can enhance the beauty of the building, so it is often the main symbol of the square.
Another example of the use of stainless steel as the main material for outdoor art buildings is the famous arch bridge standing on the river.
Stainless steel materials can be selected arbitrarily. It has a variety of different strength-to-weight ratios to meet the requirements of various building structures. In addition, different levels of surface finish also provide a range of choices for various construction facilities to meet actual needs. The architect’s bold ideas will make stainless steel increasingly widely used in the construction industry.
2. Application of stainless steel in marine installations
Various types of stainless steel are increasingly widely and successfully used in various marine environments. It must be pointed out that long-term protection of stainless steel from corrosion in seawater requires complex anti-corrosion engineering technology and a large amount of investment. Austenitic and martensitic stainless steels have long been used for superheater pipes and turbine blades in marine power plants.
It is not easy to maintain a low chloride content in these devices, because the application technology of marine power devices is not different from the basic principles of general power generation devices. Stainless steel is also being used for large-capacity chemical containers on ocean-going merchant ships, and its use is in some respects completely different from the use conditions of land-based chemical plants.
Most stainless steel grades can get satisfactory results when used in marine conditions, but different grades are sensitive to stress corrosion cracking. Martensitic steel represented by type 410 and ferritic steel represented by type 430 will rust within a few months under ocean conditions. This uniform rust can be removed by mechanical polishing.
The more popular stainless steel is austenitic stainless steel because of its strong corrosion resistance (except due to stress corrosion cracking). Over time, austenitic stainless steel will also blacken. 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.
Thruster
The propellers on tugboats and other ships on the sea can be made of cast stainless steel CF-8 (very dry type 304 stainless steel). When the ship is not sailing, it forms a conductive metal loop from the main shaft of the propeller to the hull through the bearings. Cast propellers equivalent to 410 stainless steel are also often used and are widely used in other aspects such as icebreakers.
The development of modern stainless steel technology has begun to use complex austenitic-ferritic stainless steel 20Cr-8Ni-3.5Mo to cast large propellers (up to 3000kg) on ocean-going ships.
Vessels that often work in ports are particularly susceptible to encountering logs or other floating bodies on the sea to accelerate the damage of their propellers. Therefore, the use of austenitic stainless steel to make the propeller can be repaired by straightening or welding, which is a problem worthy of attention in material selection.
Pump
It has long been observed that centrifugal pumps can show a certain degree of reliability if they use stainless steel components under seawater working conditions. In the seawater that keeps flowing, using CF-8M cast stainless steel impeller (its composition is equivalent to 316 stainless steel) and 316 stainless steel as the main shaft, there can be no problems. When the water pump stops working, crevice corrosion and pitting corrosion are likely to become serious problems.
However, if a more active and rusty cast iron is used to make a pump box with a considerable wall thickness, the cast iron can play a cathodic protection effect during downtime. When the pump is working, the cathodic protection of the cast-iron box must be able to polarize the lower rusty steel, but the flowing water remains the cathodic protection. In addition, long-term pumps may be used alternately, and sometimes seawater is replaced with fresh water for protection.
Bulk container
Stainless steel has always been used as bulk bag containers in freight transportation to loading liquefied natural gas (LNG), chemicals, beverages, etc. The LNG container used in freight transportation uses 304L stainless steel, whose purpose is not to resist corrosion but to consider the mechanical properties at low temperatures.
For containers of marine chemicals, the purpose of using stainless steel is mainly to consider its corrosion resistance, which is different from the storage and transportation of terrestrial chemicals. If the vessel is a general non-scheduled freighter, the container carrying chemicals can also transport anything, from acetic acid, lees to xylene.
Generally, 316L stainless steel is used for valves, freight pumps, pipes, heating coils, and the container itself. The container can be made of integral stainless steel or coated with a layer of stainless steel plate of 0.06¡«0.08in (1.5-2.0mm) with carbon steel. Before use, the board must be carefully checked for defects and thoroughly cleaned and passivated.
Experiments have shown that the container with chemicals is allowed to be rinsed with seawater, but it must be rinsed with fresh water soon. For any stainless steel heating device in the container, do not start it to prevent stress corrosion cracking before the chloride is completely washed away. When designing chemical containers, they should not be considered for holding seawater because doing so will lead to the risk of crevice corrosion.
If the design plan stipulates that it must be used to hold seawater, then a cathodic protection system must be considered to control the development of crevice corrosion. In this case, stainless steel containers may produce lime deposits that are difficult to remove, which is a problem worthy of attention.
Heat exchanger
Austenitic stainless steel pipes have been widely used in the cooler of the forced water circulation system and the steam condenser of the power station. The water inlet of the latter is not suitable for copper alloy materials due to high pollution. The more popular and good material is 316 stainless steel. In coastal and harbor areas, a large number of foreign clumps and silt entering the condenser pipe are particularly likely to cause serious obstacles. Measures must be taken to eliminate this situation. A reasonable measure is to use rubber balls to circulate through the pipeline.
The rubber balls can squeeze to clean the pipe wall. When the flow speed of seawater is about 1m/S, it can prevent marine organic debris from being sucked in, thereby protecting the condenser pipe from pitting corrosion. Unlike other non-ferrous alloys, the pipes using stainless steel as the condenser are not limited by the maximum flow rate, but it is related to the economic effect of the entire pump device.
O-ring
Series electrical connectors and related O-ring positioning devices are widely made of 304 and 316 stainless steel, especially for marine and military engineering. Satisfactory results can be obtained by using the above materials. The O-ring seal can be cathodic protection through the hull, aluminum frame, or other factors. If there is no cathodic protection effect, the fineness of the O-ring seal will soon (some within a few weeks) produce cracks and cause a serious failure.