Page 265 - Valve Selection Handbook

252 Valve Selection Handbook

When considering the use of rupture discs in combination with pres-
sure relief valves, the designer should follow the applicable design code.
Reordering Rupture Discs

When reordering rupture discs, the user should always quote the lot or
batch number to ensure the supply of the correct replacement disc. The
user should also be aware that the requested burst pressure only needs to
fall within the manufacturing range of the ordered disc to meet the manu-
facturer's obligations. The rated or marked burst pressure can therefore
vary between orders of the same rupture disc.
User's Responsibility

The user's personnel must be fully aware of the handling, storage,
installation, and maintenance requirements of rupture discs. Under no
circumstances should the installation be entrusted to a person who is
unaware of the installation requirements and the consequences of
improper handling of rupture discs.
Each plant should maintain a system that records location and specifi-
cation of installed rupture discs, the date and history of rupture disc fail-
ures, the agreed-upon replacement periods, and ordering and storage
instructions. The consequences of any misunderstanding can be costly.
In general, only personnel trained in the selection, installation, and
maintenance of rupture discs should be entrusted with specifying, procur-
ing, and installing rupture discs.

Explosion Venting

Explosion Vent Panels. Many powders used in the industry as well as
flammable gases form explosive mixtures when dispersed in air. On igni-
tion, such mixtures will explode and nearly instantly cause the pressure
to rise to a level that would rupture low-strength enclosures with inade-
quate venting.
When the risk of such explosions exists, low-strength enclosures are
provided with vent panels, commonly of either rectangular or circular
shape, that are sized to prevent the pressure in the enclosure from rising
above a safe level. Figure 6-35 shows a typical explosion vent panel and
Figure 6-36 a comparative graph of a vented and an unvented explosion.
P stat in the graph is the burst pressure, P red is the reduced explosion pres-