Parr Instrument Safety Rupture Disc Assemblies - Manual

231M
Safety Rupture Disc Assemblies
Operating Instruction Manual
Safety rupture discs are installed in Parr laboratory
reactors and pressure vessels to protect the equip-
ment and the operator from unexpected overpressure.
These safety devices are made in several styles, each
designed to match the size constraints and the relief
flow requirements of the reactor or vessel on which it
is used. Each assembly consists of a domed, frangible
metal disc clamped firmly against a carefully machined
orifice through which the disc will rupture and release
pressure/material from the vessel if the internal pres-
sure reaches a pre-determined burst range. All assem-
blies have either a safety tee or provision for attaching
extension piping or tubing to carry any discharge to a
safe area if the rupture disc should burst. The different
rupture disc assemblies used in Parr equipment are
illustrated with listings of the particular units in which
each is installed. The rupture disc installed in each Parr
reactor or pressure vessel will function as an effective
safety device when used as directed.
It is essential that the user of this equipment read and
observe the following instructions. Rupture discs are of
such simple construction that the user will often take
them for granted. Potential hazards can occur from: im-
proper disc selection, improper installation, improper
maintenance, improper usage, overfilling, over pressur-
izing, and from failure to provide adequate venting.
General Instructions
1. Retain the disc identification tag.
All rupture discs are furnished with a metal tag
which identifies the burst rating of the disc at a
particular temperature as well as the material of the
disc. When a complete reactor system or general
purpose vessel is furnished with a rupture disc,
these tags are attached to the safety head body
prior to shipment.
When installing a replacement disc, the new tag
should be attached to the safety head body. It is
important that these tags remain on the apparatus
so that both present and future operators will be
aware of the disc rating.
2. Select the proper burst rating.
Our standard rupture discs are made of thin metal
foils which are domed. The discs are installed with
the inside of the dome (concave side) exposed to
the pressure. The general guidance for rupture discs
of this design is that their maximum operating pres-
sure should not exceed 90% of their design burst
pressure. This guidance was developed to protect
these discs from the effects of repeated pressure
pulsing. While no cycle life is guaranteed, discs
held to this 90% limit may be expected to withstand
5,000 pressurization cycles. For most Parr Pres-
sure Vessels 5,000 cycles represents many years of
service.
It should be noted that the burst pressure tolerance
of these discs is ± 5%. So to take a disc to 90% of its
design may in fact be taking it to 95% of its actual
burst pressure. This does not leave much room for
pressure excursions.
The 600 psi discs are the lowest rating offered in
the 526HC Series discs and in the 708HC Series,
800 psi is the lowest available rating. If lower relief
pressures are desired or required, the user should
install a spring - loaded relief valve on the vessel to
serve as a primary relief device, leaving the rupture
disc in the system as the fail-safe protection in case
the mechanical relief valve does not function as
intended.
Standard rupture discs can be furnished with a
declaration of conformity showing burst pressures
at room temperature. At temperature rupture discs
can also be furnished with a declaration of confor-
mity showing burst pressures at room and elevated
temperatures. Custom discs made of other than
standard materials or burst ratings can be provided
within the limits of available materials and size
constraints. A minimum of three discs is usually
required for a special order.
3. Select a suitable disc material.
The disc must be made of a material which is com-
patible with the environment in which it is used.
This is particularly important when a reactor is used
for several different purposes. A disc that may have
been satisfactory for an original application may
not be suitable in a different situation. The Alloy
600 series discs usually installed in Parr pressure
equipment will resist most chemical vapors, yet it
cannot be assumed that an Alloy 600 disc will be
suitable for all applications. Strong mineral acids,
strong organic acids and wet halogens will attack
Alloy 600 to varying degrees. If corrosion becomes
a problem, gold facing or alternate disc materials
are available.