In a low-pressure serpentine watertube boiler, how are the tubes typically attached?

In a low-pressure serpentine watertube boiler, the tubes are typically attached using expanding. This method involves mechanically expanding the tube ends to create a tight fit within the headers or drums, ensuring a secure and leak-proof connection. This technique is preferred as it maintains the integrity of the tube material and allows for thermal expansion, which is essential in boiler operations where temperature fluctuations can occur.

Welding, while a strong method of attachment, is not commonly used for watertube connections due to the potential for heat distortion and other issues associated with welding that may compromise the boiler's structural integrity. Threading is generally not suitable for boiler tubes, as it can create weak points that may fail under pressure. Seamless fittings are more applicable to connecting piping rather than being the standard for tube attachment within the boiler structure. Thus, expanding stands out as the most reliable and effective method for ensuring the safe and efficient operation of watertube boilers.