Why is copper tubing preferred over steel or cast iron in tubular boilers?

Copper tubing is often preferred in tubular boilers primarily due to its greater heat transfer rate. Copper has superior thermal conductivity compared to steel and cast iron, which means it can transfer heat more efficiently. This efficiency helps in quicker heating and higher overall performance of the boiler, allowing for more effective energy use and shorter heating times.

While good ductility is a notable characteristic of copper, which allows it to be bent and shaped easily without breaking, this trait isn't the primary reason for its preference in boiler applications. Likewise, although copper can handle high temperatures, it is usually not the material of choice for extreme temperatures where materials like steel or specially designed alloys would be more suitable. Additionally, while copper can sometimes be more expensive than steel, the focus in boiler design is typically on efficiency, performance, and longevity rather than on initial material costs. Thus, the superior heat transfer capability of copper stands out as the main reason for its preference in tubular boiler designs.