The detection and characterization of blisters on carbon-graphite mechanical seal faces

Blisters that develop on carbon-graphite mechanical seal faces are irregula rities in surface topography that result in poor sealing performance and a high incidence of catastrophic failure. On first inspection a blister is a burnished area that is slightly elevated above the surrounding seal surface . In this study, the topography of several hundred blisters was examined wi th interference microscopy. The shape of the burnished area is typically el liptical or cylindrical. The leading edge against the direction of rotation of the mating seal ring extends abruptly upward from the surrounding seal surface. The trailing surface gradually merges into the parent seal face. M ost blisters have a maximum height of 0.25 mu m to 0.75 mu m (10 mu-in to 3 0 mu-in).