One Piece Construction

This link shows an example of a one piece gasket for a process plant piping system.

http://www.flexitallic.com/pro_non_metallic_sf1630.html

This link shows an example of a multiple piece gasket for a process plant piping systems.

http://www.flexitallic.com/pro_therm_835.html

The one piece gasket would normally be used for low pressure, low temperature non-toxic fluids and gasses.

The multiple piece gasket is normally used for services with both elevated pressure and temperature as well as toxic characteristics.