Understanding Boiler Steel Plate and Usage

Boiler steel plates are among the crucial materials in boiler manufacturing, primarily referring to the hot-rolled special carbon steel and low-alloy heat-resistant steel plates used for manufacturing important components in boilers such as boiler shells, drums, headers, end caps, support brackets, etc.

Boiler steel plates often operate under conditions of medium to high temperature and pressure. Apart from withstanding high temperatures and pressures, they are also subjected to impact, fatigue loads, corrosion from water and gases, making the working conditions harsh. If a boiler suffers a catastrophic failure during operation, it can lead to serious losses.

Therefore, boiler steel plates must possess excellent physical properties, mechanical properties, and workability, with strict requirements outlined in material standards to ensure safety during usage.

Boiler Steel Plates

Classification by Material

From a material perspective, boiler steel plates can be classified into two categories: special carbon steel plates and low-alloy heat-resistant steel plates. The materials used for boiler steel plates have strict control over chemical composition, especially harmful elements such as phosphorus, sulfur, and residual elements like chromium, nickel, copper; During smelting, good deoxidation and removal of non-metallic inclusions should be carried out to ensure good plasticity and toughness; Uniformity in microstructure is required, with grain size controlled within a certain range (usually aiming for a grain size between 3 and 7); Strict requirements are set for surface quality and internal defects; Furthermore, mechanical properties at both room temperature and high temperature must be guaranteed.

The GB/T713-2014 “Steel Plates for Boilers and Pressure Vessels” standard clearly specifies that oxygen converter or electric furnace smelting should be adopted and refining treatment should be carried out outside the furnace during manufacturing. It is also required to ensure that the compression ratio of continuous casting billets to steel ingots during hot rolling is not less than 3.

Classification by Operating Environment

Based on different working conditions, boiler steel plates can be divided into two major categories: steel plates for manufacturing room temperature and medium temperature pressure-bearing components, and steel plates for manufacturing high-temperature pressure-bearing components.

Boiler steel plates for room temperature and medium temperature (below the creep temperature) mainly use carbon steel, including carbon steel, carbon-manganese steel, and carbon-manganese-silicon steel, namely Q245R, Q345R (20g, 22Mng, 16Mng, 19Mng steel in GB/T713-1997 “Steel Plates for Boilers”), as well as ASME SA-515/SA-515M “Carbon Steel Plates for Medium and High Temperature Pressure Vessels,” SA-299/SA-299M “Carbon Manganese Silicon Steel Plates for Pressure Vessels,” etc. They are primarily used for manufacturing pressure-bearing components such as boiler drums and below-medium temperature header end caps.

Room temperature and medium temperature boiler steels require: Higher room temperature strength; Good impact toughness and low notch sensitivity; Due to the extensive cold deformation required during processing of components like boiler drums, they also need to have good aging toughness; Good processing and welding properties; Good low magnification structure, etc.

For high-temperature (above the creep temperature) boiler steel plates, low-alloy heat-resistant steels are generally used, including chromium-molybdenum steel, chromium-molybdenum-vanadium steel, chromium-molybdenum-tungsten steel, etc. They are mainly used to manufacture high-temperature pressure-bearing components such as high-temperature header end caps and steam pipe plugs.

Examples include 15CrMoR, 12Cr1MoVR in GB713-2014 Boiler Steel Plate, Gr22, Gr91 in ASME SA-387/SA387 M Pressure Vessel Use Chromium-Molybdenum Alloy Steel Plate, and Gr23, Gr911, Gr122 in ASME SA1017/SA1017M Pressure Vessel Use Chromium-Molybdenum-Tungsten Alloy Steel Plate.

High-temperature boiler steel plates must possess: Sufficient high-temperature endurance strength and ductility; Good high-temperature microstructure stability; Good high-temperature oxidation resistance (heat resistance); Good cold and hot working properties (mainly referring to cold bending deformation and weldability), etc.

Steel Boiler

Main Characteristics of Boiler Steel Plates

As boiler steel plates are products of crucial importance with strict safety and reliability requirements and high manufacturing technology difficulty, they must possess the following main characteristics: High yield strength performance within a certain temperature range (at room temperature, medium temperature, and high temperature); Sufficient toughness to prevent brittle failure accidents during manufacturing or usage; Low strain aging sensitivity to ensure a certain value of aging impact toughness, especially within the corresponding working temperature range; Low notch sensitivity to prevent steel from cracking in welding, piercing, and local stress concentration areas; Good welding performance; Good microstructure without white spots and cracks.

Main Production Processes of Boiler Steel Plates

Given the main characteristics of boiler steel plates mentioned above, the production process of materials necessitates accurate composition control, low impurity elements, clean steel refining technology, precise temperature control, good dimensional accuracy, and plate shape. This requires the adoption of advanced production processes. With the progress of equipment technology and the application of advanced production processes in China, excellent boiler steel plates have been widely used.

RH Furnace Ignition

In general, the modern wide and thick plate production lines adopt the following processes in producing boiler steel plates: Desulfurization pretreatment of molten iron; Smelting production of clean steel in converters; Refining outside the furnace to remove non-metallic inclusions; RH circulation deep degassing process to significantly reduce the content of gases such as hydrogen, oxygen, and nitrogen while ensuring stable steel temperature; Advanced defect-free slab casting technology to obtain high-quality cast billets; Controlled rolling and controlled cooling processes to ensure uniform structure and grain; Precise temperature control during heat treatment, etc.

With the commissioning of large power plants and the extensive industrial application of subcritical, supercritical, and even ultra-supercritical boilers, the development of boiler steel plates as basic materials has seen significant growth. Consequently, the standard level of boiler steel plates will also undergo further development.

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