Pressure Housings are normally produced from premium high temperature alloys. Magnetic or amagnetic (non magnetic) depending on the application. Most common materials for high performance Housings are related to the family of the Inconels. Due to the high properties of these materials, they are impractical to extrude as tubes, and therefore, are machined from solid round bars. Once the steel bars have been heat treated and qualified, they are bored (or trepanned) as shown in the photograph. The trepanning operation leaves a central 'core' as the one shown of the partially drilled bar on the right. In down-hole applications, these Housings are subjected to external pressures. In order to survive these very high crushing pressures, the wall thickness of the tubes must be very uniform so that all the collapsing stresses are balanced. The trepanning is done with specialized techniques and machines, and the resulting wall thickness is charted and filed with the Housing's QC information.
Once the Housings are in a tube form, the ends are machined to the customer's needs and specifications, which normally require threads and sealing surfaces. The last qualifying step is pressure testing the housing to confirm it's pressure rating.