Ferritic heat-resistant steel has excellent thermal conductivity, low expansion coefficient, good resistance to intergranular corrosion, stress corrosion resistance, and low production cost. It is the preferred steel grade for steel for seamless steel pipes
of boilers. It is 20g, 15crmo, 12cr1mov, cr5mo, cr9mo, T11, T12, T22, T91, T92, and the like.
Boiler seamless pipes
are mainly used for:
1. Water wall tube
It is used to absorb the radiant heat in the furnace and heat the water to saturated steam while protecting the fireplace. Steel for water wall pipe generally requires a certain room temperature and high temperature strength, good high temperature durability and creep resistance, excellent corrosion resistance, especially excellent welding performance.
The reducing atmosphere in the lower part of the boiler furnace causes the thinning of the water wall tube, which is more serious when using high sulfur coal. According to the temperature used by the water wall tube, the steel type is not the same.
2. High temperature superheater / reheater
High-temperature superheater tube: heating saturated steam into superheated steam with a certain temperature, which is divided into several stages for heating; reheater tube: used to send the steam for doing work back to the boiler and then send it to the steam turbine for work.
The boiler's final superheater and reheater seamless tubes have the highest performance requirements in the boiler components, the most complex and severe service conditions, and 30-35 ° C higher than the rated steam temperature. The boiler tube used has ultra-high temperature endurance strength and
creep strength, and also needs to meet a certain degree of corrosion resistance: anti-pipe material outer wall smoke corrosion, dust particle corrosion, oxidation resistance.
3. Pipelines and headers
The outlet header and the main steam and reheat steam pipelines are located outside the furnace, which are less affected by the corrosion of the flue gas, and require less corrosion resistance of the material, and the temperature of the part of the pipe wall is substantially equal to the steam temperature.
At present, the pipeline and the header are made of ordinary medium alloy ferritic heat-resistant steel, which has a low coefficient of thermal expansion and a high thermal conductivity.
In summary, boiler ferritic heat-resistant steel generally works in high temperature, high pressure and steam corrosion for a long time. In this environment, the steel properties will deteriorate rapidly, which will affect the operation of the equipment, while ferritic heat-resistant steel can be very good. Meet this need. However, due to the high temperature strength, it cannot be used at higher temperatures. To this end, people are developing new types of ferritic heat-resistant steels, such as ODS steel, but at a higher cost, it seems that it is not suitable for a wide range of applications.