Discs may be simple, no more than a shaped piece of metal foil, or of various
degrees of complexity. Simple discs usually have re-usable holders, whereas
complex ones come as assemblies built into their holders. But
while the former are therefore more economical, the latter are more reliable
and accurate. Usually, in oilfield applications, the cost of an operation
going wrong is huge, when measured correctly to include down-time, lost
production and recovery costs, and it is poor economy to save a little
but to risk a lot.
Consequently, Benoil does not list and rarely supplies simple discs. Products
are usually fully welded assemblies, with the foil welded between two metal
rings. There are also fully clamped versions as assemblies, ones which cannot
be adjusted by the user from the pre-set arrangement. Discs can be held in
place with a secondary mechanism (circlip, external screws) but for most
applications are self-threaded for fixing. The chief exceptions are the
original cementing darts (see catalogue section 6), which are rubber
over-moulded to slide, and not be fixed, in the tubing.
The seating and porting of a burst disc will depend on its application. Benoil
will design an assembly to have a metal-metal seal, a carried O-ring seal, a
chamfered O-ring seal, or whatever else is appropriate. There tends to be a lot
of interaction in the overall design between the space or wall section available
for a port, the type of seal, the size and position of any O-ring, and the
requirements of burst pressure and orifice size. Benoil tackles the design
using SolidWorks CAD to ensure the parameters fit together to meet the need.