When plugging a straight tube exchanger, which head does not need to be removed?

In the context of plugging a straight tube exchanger, the correct answer is the tub head. The tub head, also known as the tube sheet or tube head, is typically a fixed component that secures the tubes in place and is designed to allow access to the tubes for maintenance and repair. When plugging or sealing tubes, you can often access the necessary tubes from the tub head without the need to remove it.

Removing other components like the channel head or the floating head is usually necessary to facilitate access to the corresponding tubes or for the purposes of inspecting or repairing the heat exchanger. The dollar plate, which connects various components of the exchanger, may also need to be removed to allow for proper access. Therefore, the tub head remains in place during the plugging process, making it distinct from the other heads that may require removal.