Boiler tube

Boiler tube quality problems

Boiler tube quality problems mainly in the cracks, shrinkage, peeling, pit, layered, pinhole, slag and so on. Boiler tube defects and injuries that may exist in the same smelting and rolling process. The main defects in the surface of the boiler tube and an outer surface than the inner surface. About 70 percent of these defects from the raw material (billets), billets in blowing insufficient residual slag material, shrinkage, etc., with which there may be rolled steel transverse cracks, laminated, folded, heavy leather and other defects, longitudinal cracks caused mostly rolling strain. If the boiler tube in the emergence of these defects or injuries, considers the material appeared discontinuous density within the material is damaged, it is possible leaks in the hydraulic pressure test, boiler pressure element is made at run time there may leak or burst pipes. Because of this, in order to ensure the quality of boiler pipe, whether it is related to a foreign country or boiler seamless steel pipe standards are clearly defined, as the process performance guarantee, steel hydraulic test should be made by the root.

The purpose of the hydrostatic test, there are two: one is the process of hydraulic test, its purpose is to test the material (or components) for leaks, that the sealing properties of materials; the other is the verification of the hydrostatic test, its purpose is to strength test material (or components) is adequate. From here, the hydrostatic test pressure boiler tube is part of the process of trial, is the material density test, if the test material is dense and continuous; it is not the strength of experimental verification. Strength theory of mechanics of materials known from, seamless steel components are thin and long, and its diameter is very small, even for thin-walled tubules can withstand a lot of pressure.

Boiler tube thermaL fatigue

Stratified soda boiler heating surface tubes, economizer tubes stuffed steam super heater with water, temperature and pressure relief valve is opened by intermittent, will cause the temperature of the slide, resulting in alternating thermal stress, thermal fatigue cracking. Also, in the action of corrosive media, these fatigue cracks on the tubes in particularly vulnerable to such rough surface, the larger scratches, corrosion pit corrosion rate has the notch area, so called corrosion resistance to thermal fatigue cracking. Hot corrosion fatigue cracks generally showed plexiform single line distribution, and perpendicular to the stress direction. In the inner wall of the lateral cyclic crack, crack shorter with fatigue fracture is characterized by brittle fracture.

Boiler heating surface tubes during operation, the wall directly with the high-temperature steam smoke, water and steam into contact, will produce other corrosion, damage caused by premature rupture of the pipe. Such as work in the open air as the air preheater, etc., due to fumes in SO2, but also produce low-temperature corrosion damage.