Nubbins are predominately machined into a heat exchanger flange to create a high stress point to produce a tighter seal.
Traditionally the gasket used when a nubbin is present is a Double Metal Jacket (DMJ), which consists of a metal jacket with a soft internal sealing material e.g. Graphite, PTFE. The metal jacket is commonly soft iron, carbon steel or a 300-series austenitic stainless steel.
This paper will compare the performance of a DMJ and Kammprofile gasket, performance being – leakage and temperature cycling and the affect the nubbin has on the gasket after testing.