What precautions should be taken when cold-working (such as bending) STBA20?
Extreme caution is required when cold-bending STBA20. Due to its high strength and hardness, as well as its certain hardenability, cold-working can produce significant work hardening, resulting in increased wall hardness and decreased toughness. Therefore, the bend radius during cold bending should not be too small, typically requiring no less than four times the tube's outer diameter, to avoid excessive deformation and microcracking. For thick-walled tubes or those undergoing large deformations, stress relief annealing is recommended after cold working to eliminate processing stresses, restore the material's toughness, and prevent problems during subsequent use or welding.
What is the process for hot-working (hot bending or hot forming) STBA20?
Hot-working is the preferred method for forming STBA20, but it requires strict process control. First, the steel tube should be uniformly heated to an appropriate temperature range, typically between 850°C and 1050°C, ensuring uniform heat distribution. Overheating and excessive surface oxidation should be avoided during the heating process. Forming operations should be completed within this temperature range. After processing, components must be slowly cooled or immediately normalized and tempered to restore their normal microstructure and mechanical properties. Never allow them to cool rapidly in air.
What are the key considerations when installing STBA20 piping systems?
When installing STBA20 piping systems, the first priority is to ensure that all pipe sections and components are clearly and accurately labeled with the correct material to avoid mixing with lower-grade materials (such as carbon steel). Second, installation must strictly follow the design drawings, ensuring that supports and hangers are correctly set to avoid placing additional stress on the piping. Third, all welding work must be performed by qualified welders using approved welding procedure specifications (WPP/WPS), with strict preheating, interpass temperature control, and post-weld heat treatment. Finally, throughout the installation process, pipe ends must be protected to prevent foreign matter from entering the pipe.
Why should temporary attachments be avoided on STBA20 piping?
It is strictly prohibited to weld temporary attachments such as brackets and lugs on STBA20 piping. Any uncontrolled welding creates an unheat-treated heat-affected zone (HAZ) with a hardened martensite structure in the base metal. This zone is extremely fragile and easily serves as a starting point for crack initiation. These cracks can propagate under the high-temperature and high-pressure operating conditions of the equipment, potentially leading to catastrophic leaks or pipe bursts. If welding of accessories is necessary, it must be performed according to a formal welding procedure, including preheating, the use of compatible welding consumables, and post-weld heat treatment.
Why is post-installation cleaning of the STBA20 piping system important?
Post-installation cleaning (purging or chemical cleaning) is a crucial step before commissioning. Its purpose is to thoroughly remove all impurities, such as scale, welding slag, grease, and sand, that remain inside the piping during fabrication, transportation, and installation. If these impurities are introduced into the boiler or turbine, they can cause serious damage: wear on high-speed rotating blades; block narrow pipes or heat exchange tubes; and, at high temperatures, deposit and form localized hot spots, leading to overheating or even pipe bursts. Therefore, a rigorous cleaning procedure is essential to ensure internal cleanliness of the system.
