The IX Seal-rings are designed and used where the NORSOK CFC (Compact Flange Connections) are in use. The rings come in three different kinds of steel and are coated with PTFE in varying colours in order to distinguish between them. Standard identification NORSOK STANDARD L-005 (NCF5).
link:http://www.gasket-china.com/gasket/ring-joint-gasket/high-temperature-ix-ring-joint-gasket.html