Pressure Vessel Components

Shell  - The shell in most vessels is what provides the longitudinal length of the vessel.  Or all vessels, the thickness of the shell is based on the pressure the shell will see (both internal and external), plus any additional loads created by the supports, nozzles or other attachments.  Most shells are circular in shape.  This is based partially on economics of forming the shell but mostly is due to the equal distribution of forces on the circular shape.

Head  -  A head is one of the end caps on a cylindrically shaped pressure vessel.  The inward pressure of each type of head determines the range of its use.

• Dish Radius  -  Also know as crown radius.  It is the major radius of the formed head, usually measured from the inside.
• Inside Depth of Dish  -  Measurement from the inside center of the head to the tangent line.
• Knuckle Radius  -  Also known as corner radius. It is the formed radius of the head which transitions the dish portion to the straight flange. This process is done on a flanging machine.
• Straight Flange  -  Is the straight portion of the head measured from the tangent line to the edge of the head.  The industry standard is 1 1/2".
• Tangent Line  -  The point on the head where the knuckle radius meets the straight flange.  Refers to the point of contact, tangency, between the cylinder and the knuckle portion of the vessel head.  The distance from the tangent line on one head to the tangent line on the opposite head is known as the straight side or tangent-to-tangent.

Nozzle  -  Nozzles are inserted into the shell or head and are the first step of what connects to the process piping.  Nozzles can connect to flanges or threaded fittings depending on the design.  Nozzles must be designed depending on the metallurgy of the shell & nozzle, internal and external projections of the nozzle, orientation of the nozzle and  internal and external forces on the nozzle, such as pressure and piping forces.

Slirt and Legs  -  The saddle is another designed component which carries the weight of the vessel.  A saddle is a plate that supports a pressure vessel and connects to the foundation.  The design of this component takes the physical dimensions of the vessel (weight, length and design) and external forces (Seismic Zones and Wind  Forces, for example).

Internals  -  Pressure vessels usually have internals that are specific to the process.  Click on for more reading on Vessel Internals.