Boiler plates are high temperature service stainless steel plates that are intended for high temperature services with high pressure, oxidation resistance and corrosion resistance. The structural steel plates are intended for high wear and tear, high strength and corrosion resistant applications. There are different material grades that are used for different application requirements with different mechanical properties.
Grades and mechanical properties of boiler plates and structural steel plates
The structural steel plates are used in the construction industry mostly. Their yield strength has to be stronger. There are S235, S275, S355 and other grades of structural steel plates. The S355 has a yield strength of 355MPa and the tensile strength ranging between 470-630MPa. It has 7850kg per meter cube of density and high hardness in the range of 146 to 186 HB (Brinell Hardness). The structural steel plates also have to be high wear and tear. Often the different types of materials used have the chemical composition with high carbon content and alloying materials such as the tungsten to increase the strength and wear and tear properties of the steel. The boiler plates on the other hand have to have high temperature resistance. The A516 for instance has high tensile strength at 70-90ksi and minimum yield strength of 38ksi. It could be used integrated with applications that deal with boilers, heat exchangers, pressure vessels and valves. It has carbon, silicon, manganese, phosphorus, sulfur, alumimum and chromium in its composition.
Variations of steel plate grades
The different grades of plates and their composition make the difference between the mechanical properties. The mechanical properties in turn determine the application of the plates. There are plates made in the A36, A572, A588, 1045, A514, 4130, 4140 and 4340 grades.
The A36 is the commonly used structural steel for plates. Its tensile strength ranges from 400 – 550MPa. It can operate under temperatures up to 427 degrees Celsius. The A572 is a columbium vanadium steel that has minimum yield strength of 50,000PSI. It is very much resistant to atmospheric corrosion which makes it applicable in outdoor steel structures. Another structural steel grade is the A588 which is a weathering steel that forms an oxide layer on the outside and remains corrosion resistance for the rest of the time. It is also called corten steel.
The ASTM A516 is a pressure vessel class of carbon steel that is used for moderate to lower temperature services of pressure pipes and boilers. It has a tensile strength ranging from 55ksi to 70ksi. The ASTM A387 is a chromium molybdenum steel plate grade that is used in boilers for elevated temperature services. There are grades 5, 11, 12 and 22 of this specification that can meet the different requirements of boiler plates. Each grade has a Class1 and Class 2 with slightly different mechanical properties as well.
Selection of different plate types
There are different manufacturing procedures involved in making the plates. Two of the major types are the hot rolled plates and the cold rolled plates. The hot rolling procedure is conducted under hot conditions where the cold rolling takes place under low temperatures. The hot rolled plates are heated above the recrystallization point of steels at high temperatures so that when created, these plates are easy to work with. The hot rolled plates could come up with scaly surface and slight distortions due to the rapid cooling after the shaping of the plates. The structural applications can use the hot rolled plates. The boiler plates however need more accuracy in dimensions and on the surface. They cannot have serrated edges, deformations or scaly surfaces because of the high temperature and pressure operations combined with boiling ingredients. So the cold rolled plates are preferred. The hot rolled plates are re rolled under room temperature to eliminate the deformations, scaling and any other inaccuracy in dimensions. This makes them costly but better for smooth surface and less corrosive due to less friction on the surface.