Page 227 - Valve Selection Handbook

6

RUPTURE DISCS

Rupture discs are the pressure and temperature sensitive element of
non-reclosing pressure relief devices, consisting of the rupture disc and a
holder. They are designed to protect pressure systems against damage
from excessive overpressure or vacuum by bursting at a predetermined
pressure differential across the disc.
The original rupture disc consisted of a plain metal sheet that was
clamped between two flanges. When exposed to pressure on one side, the
disc would stretch and form a hemispherical dome before bursting. The
predictability of the burst pressure, however, was poor. To improve the
predictability, rupture discs were subsequently predomed by applying
pressure to one side of the disc that was higher than the normal operating
pressure by some margin.
The rupture disc thus produced is today's solid-metal forward-domed
rupture disc. Flat metal rupture discs have also been reengineered for
low-pressure applications. Both types of rupture discs are of the tension-
loaded type in which the fluid pressure stretches the disc material as the
fluid pressure increases.
The continuing effort to raise the operating ratio of rupture discs led to
the development of reverse-buckling discs. This type of disc is domed
against the fluid pressure so that the fluid pressure introduces a compres-
sion load on the convex side of the disc.

214