Boiler tubes up to but not including 2-inch OD tubes must project into drums or headers at least how many inches?

The requirement for boiler tubes up to but not including 2-inch outer diameter (OD) to project into drums or headers by a minimum distance is critical for ensuring proper heat transfer and operational efficiency. The specified range of 3/16-5/16 inches ensures that there is adequate engagement of the tube within the header or drum. This projection helps prevent leaks, maintains structural integrity, and facilitates the effective exchange of heat between the water and the gases produced during combustion.

When tubes do not meet this minimum projection, they may lead to inadequate sealing at the connection points, increasing the risk of water leaks and reducing the effectiveness of heat transfer. The careful specification of this dimension is thus crucial to the overall safety and efficacy of the boiler operation.

Other ranges provided in the options do not align with the established standards, which have been set to ensure reliability and safety in boiler operations.