Casing head is the lower part of the wellhead that is almost connected to the surface casing string and provide a means of suspending and packing off the next casing string. It is a simple metal flange welded or screwed onto the top of the conductor casing or casing to form part of the wellhead. It is a primary interface for the surface pressure control equipment such as BOP or Christmas tree.
The casing head after or when installing is usually tested to avoid leakage under BOP condition, before any surface equipment is installed. It is typically qualified to withstand up to 10,000psi working pressure. Its terminate the need for lock-down screws to retain the bowl protectors, creating fewer leak paths. The bottom prep of the casing head can be machined to fit a variety of application.