What portion of the steam drum contains a manhole for access to the drum for cleaning, inspection, and repair?

The drum head is the correct answer because it refers to the top or end of the steam drum where a manhole is typically located. This component is designed to provide access for maintenance tasks such as cleaning, inspection, and repair of the internal surfaces of the drum itself.

Manholes in the drum head allow machinist mates to enter the steam drum safely when necessary, which is crucial for ensuring that the steam generation system operates efficiently and effectively. The steam drum serves as a reservoir for water and steam in a boiler system, and having access to it is important for maintaining the overall health and functionality of the boiler.

The other options do not serve this specific purpose: the blow-off head is associated with the blow-off valve for draining sediment, the top header is part of the water distribution system, and the steam chest is used for the collection of steam before it is sent to other systems. Thus, only the drum head properly encompasses the manhole for direct access to the steam drum.