How are boiler components subjected to induction annealing?

Whether parts made of bent or welded steel pipes and steel plates should be heat treated depends on the material of the steel pipe or steel plate, the outer diameter and wall thickness of the steel pipe, the thickness of the steel plate, whether the deformation is cold deformation or hot deformation, the degree of deformation and the welding method used. Methods will be determined in detail. Usually, cold-formed steel pipes with large deformations generally need to be stress-relieved and tempered. Even if large-size thick steel plates are hot-rolled at high temperatures, they should be normalized and tempered afterwards. Fire treatment; in order to refine the grains and improve the mechanical properties of the welded joints, large-size rear plates need to be normalized and tempered after electroslag welding.

The manufacturing process of "four tubes" such as water-cooled walls is:

Design - blanking, bending or welding - assembly and welding to form a film-type water-cooled wall tube screen, or assembly into a serpentine tube bundle such as a superheater - power plant placement, welding, and installation. The "four tubes" such as the water-cooled wall and superheater are connected to the steam drum, each header and the main steam pipe through ducts, forming a circulation loop of the boiler - the water-cooled wall tube panels form the furnace walls on all sides of the boiler; the ceiling superheater and cladding The superheater constitutes the furnace top and flue; the serpentine tubes hung side by side above the furnace serve as front and rear screened heaters and reheaters; the serpentine tube bundle in the flue forms an economizer, etc.

The boiler drum is an extra-large structural member made of thick steel plates through complex processes. Its processing route is: design - blanking - heating the steel plate at high temperature and stamping it with a hydraulic press into semi-circular heads at both ends of the drum - whole A steel plate is heated at high temperature and hot-rolled into a cylinder shape - longitudinally welded into steam drum barrel sections, normalized and rounded - two heads and several barrel sections are assembled and welded into a steam drum - normalized in a large annealing furnace Tempering treatment - after various processing and welding, stress relief treatment, it becomes the finished product of the boiler drum.

Weld thickness heat treatment methods are divided into two types: post-weld heat treatment with heating in the furnace and post-weld heat treatment with local heating of the welding part. Post-weld heat treatment with furnace heating requires parts to be put into the furnace at one time in principle. When it cannot be loaded into the furnace at one time, such as the 29m extra-long boiler drum of the 600MW unit, it can be heated in two sections, but the overlapping heating area should be greater than 1500mm; insulation measures should be taken at the outside of the furnace to avoid excessive temperature gradients. The external parts of the furnace should be reasonably placed with supports to prevent harmful thermal expansion and contraction. The temperature of the heated parts should be less than or equal to 400 degrees Celsius. When heating, avoid direct contact of the flame with the workpiece. For post-weld heat treatment with local heating, the type and form of the heating device used are not limited, but the heating width of the welding zone is greater than twice the thickness of the steel plate. When using local heating post-weld heat treatment, the temperature gradient between the heated parts and the non-heated parts should be minimized.