The term heat exchanger in most process industries is referred to as the «shell and tube heat exchanger». As the name implies, it is equipment that as a «shell» and a bundle of «tubes». One of the fluids flows inside the shell and outside the tubes and the other fluids inside the tubes.

The 927 gasket is similar to the 923 style gasket but it is made with a flexible graphite corrugated tape on each side. This cover increases the gasket sealability, especially if the flange sealing surfaces have pitting, tool marks or other small irregularities. The flexible graphite fills these irregularities and, in turn, increases the sealing.