What two sheets of steel make up the construction of the steam drum?

The correct answer identifies that the steam drum is constructed from a wrapper and tube. The wrapper, or outside layer, provides structural integrity and containment for the steam and water mixture, while the tube material allows for heat exchange and facilitates the circulation of water and steam within the drum. The combination of these two components ensures that the steam drum can withstand pressure and temperature changes during operation, making it a crucial part of a steam generation system.

The other choices do not accurately describe the components of a steam drum. The frame and casing typically refer to elements of the overall support structure, while tube and plate may suggest different functions not related specifically to the drum's construction. Understanding the roles of the wrapper and tube will help better comprehend steam drum design and functionality in a machining context.