أنابيب الفولاذ المقاوم للصدأ في تطبيقات سخان مياه التغذية

ملخص

Stainless steel tubes are commonly used in Feedwater Heater Tube (FHT) applications across industries, including nuclear energy and boilers. In the boiler market, these tubes are utilized in both industrial and utility boilers, which vary in size, design, and applications. As previously discussed, stainless steel is available in various grades to suit different FHT needs. This article will compare stainless steel welded tubes and seamless tubes to aid in decision-making.

تحديد

Here are the two most popular specifications for producing stainless steel tubes for FHT:

ASTM A213/213M: This standard specifies seamless ferritic and austenitic alloy-steel tubes used in boilers, superheaters, والمبادلات الحرارية.
ASTM A249/A249M: This standard covers welded austenitic steel tubes for boilers, superheaters, مبادلات حرارية, and condensers.

Economic Considerations

Producing stainless steel seamless tubes involves more complex processes than welded tubes, making them more expensive for the same dimensions. Seamless tubes, made from round bars without welding seams, are often viewed as superior in corrosion resistance and pressure-bearing capabilities. Weld seams can be weak points if not properly managed, but this does not imply that welded tubes are of inferior quality.

Welded tubes have their advantages, such as lower production costs, better surface finish, and more uniform thickness. The technology used by VHET for producing welded tubes under ASTM A249/A249M is advanced and widely used in FHT applications. Both seamless and welded tubes produced according to these specifications are suitable for their intended purposes. Ignoring economic factors, it is crucial to understand more about stainless steel welded tubes for FHT applications.

Advantages and Disadvantages of Stainless Steel Seamless Tubes

Seamless tubes are made from stainless steel bars and lack welding seams, offering certain advantages. They are typically small in diameter, around 15–18 mm OD for FHT applications, and usually less than 90 mm for utility boilers. Through several drawing processes, seamless tubes can achieve uniform thickness.

لكن, seamless tubes involve more processes, leading to longer delivery times and higher costs. Customization can take 2 ل 3 months, and the finish may not be as smooth as welded tubes.

Advantages and Disadvantages of Stainless Steel Welded Tubes

Stainless steel welded tubes produced under ASTM A249/A249M are distinct from general-purpose welded tubes, mainly due to the online annealing process. The advantages of this production method include:

No Carbon Contamination
- VHET technology eliminates the need for lubricants during formation or reduction processes, preventing carbon contamination during annealing. في المقابل, seamless tubes require lubricants and degreasing, which can be challenging to achieve on the inside walls of long tubes.
Minimum Residual Stress
- The online annealing process keeps welded tubes straight, minimizing residual stress. Seamless tubes require straightening, which can introduce stress marks and increase residual stress, negatively affecting stress corrosion resistance. على سبيل المثال, الفولاذ المقاوم للصدأ 304 is vulnerable to stress corrosion in high-temperature and high-pressure conditions.
No Risk of Chromium Depletion or Overpickling
- Seamless tubes need pickling to remove oxide and chrome-depleted layers after annealing. Due to their length and small diameter, this process is difficult and can lead to incomplete chrome removal or overpickling, resulting in a rough finish and increased pressure drop. Welded tubes produced with VHET technology avoid these risks, as no pickling is required.

Overall, while both seamless and welded stainless steel tubes have their pros and cons, they can both effectively serve their intended applications in FHT systems.