Introduction
The Sigma EXL™ Reverse Buckling Rupture Disk (Bursting Disc)
has been developed to provide the highest operating pressure capability available
from a Rupture Disk (Bursting Disc)
pressure relief device. Sigma
EXL™ Rupture Disk (Bursting Disc) technology and the SRB-7RS™ Safety Head
combine the accuracy and reliability of Reverse Buckling Disk technology with
unique disk and safety head design features that enable the Sigma EXL™ disk to
operate to 95% of the Marked Burst Pressure (100% of Minimum
Burst Pressure according to CEN ISO 4126-2 standards). The Sigma EXL™ Rupture
Disk (Bursting Disc) embraces SafT technology, Structural Apex Forming, the
central feature on the disk dome enhancing burst pressure accuracy.
At its burst pressure, the Sigma EXL™ Rupture Disk (Bursting
Disc) dome reverses and opens by shearing around a circular score line located
near the perimeter of the dome. The score line engages with one or more points
on the integral hinge down stream of the disk.
The disk opens around its circular score line with the
central petal supported by the hinge, avoiding fragmentation.The Sigma EXL™
Rupture Disk (Bursting Disc) is offered with a simple burst pressure tolerance.
No Manufacturing Design Range needs to be considered for
this high Operating Ratio disk (effectively a 'zero' range disk).
The performance of every Sigma EXL™ disk is assured by proof
pressure testing each disk to its maximum recommended operating pressure. The
Sigma EXL™ Rupture Disk (Bursting Disc) provides the user with the highest
Operating Ratio of any Rupture Disk (Bursting Disc) pressure relief device.
For users who wish to obtain the enhanced quality assurance
testing of this disk design, and can accept more traditional Reverse Buckling
Disk accuracy, the Sigma™ Rapture Disk
is offered with a -5% Manufacturing Design Range.
Sigma EXL™ and Sigma™
Disk Features
• Reverse
Buckling Disk in Sizes 1"-8" (25-200 mm)
• High
Operating Ratio: 95% of marked burst pressure
• High
Operating Ratio: 100% of minimum burst pressure (CEN ISO4126-2)
• Standard
0% Manufacturing Design Range, optional -5%
• Designed
for non-fragmentation
• Designed
for Gas, Liquid, or two-phase flow conditions
• Fail
Safe: Damage- Safety Ratio <1
• Saf™
technology
• Vacuum
resistant
• Smooth
process side of disk resists product accumulation
• Long
service life in pressure cycling or pulsating conditions
• US Patent
No.5167337 and worldwide patents pending
• For
installation in BS&B type SRB-7RS™ Pretorqued Safety Head
Manufacturing Design
Range
Manufacturing Design Range (MDR) is a range of pressure,
always applied to the minus side of the user's requested burst pressure , that
simplifies disk fabrication testing and provides an economic benefit to the
user where such an added tolerance can be accommodated by the application. The Sigma EXL™ Rupture Disk (Bursting Disc)
has a standard "0%" MDR, and the Sigma™ Rupture Disk (Bursting Disc)
less a "-5%" range.
Burst Tolerance
Burst tolerance is the range of pressure over which a
rupture disk (bursting disc) is expected to burst, expressed as a
"+/-". Both Sigma EXL™ and
Sigma™ disks have the same burst tolerance.
Damage Safety Ratio
< 1
If a Sigma EXL™ or Sigma™ Rupture Disk (Bursting Disc) is
accidentally damaged, it will relieve pressure by bursting at or typically
below its marked burst pressure. This failsafe design feature is called the
Damage Safety Ratio, and with a value of 1 or less, will ensure that the Sigma
EXL™ or Sigma™ Disk will, if damaged, relieve pressure at a reduced burst
pressure. A damaged Sigma EXL™ or Sigma™ Rupture Disk (Bursting Disc) will
typically reverse and then open at a reduced pressure.
Operating Ratio
Sigma EXL™ Reverse Buckling Disks can sustain operating
pressures to 95% of their marked burst pressure, or to 100% of their minimum
burst pressure. (For disks certified under CEN ISO 4126-2 'Performance
Tolerance', the Sigma EXL™ disk can sustain operating pressures to 100% of the
burst pressure less the negative performance tolerance.) Sigma™ Reverse
Buckling Disks having a -5% Manufacturing Design Range may also sustain operating pressures to 95% of their marked
burst pressure, or to 100% of their minimum burst pressure. However, this
operating pressure may be lower than for a Sigma EXL™ disk by as much as the
-5% MDR.
Materials
The Sigma EXL™ and Sigma™ Rupture Disks are available in a
range of corrosion resistant materials (see table). For each material the upper
temperature limit has been determined from the recommendations of material manufacturers and user
experience. While Hastelloy C-276 is the standard grade used, Hastelloy B and
Hastelloy C-22 may be available upon request.
Fluorocarbon film liners are available as an additional
corrosion barrier attached to the process side of the
Rupture Disk (Bursting Disc). FEP is the standard liner material. PFA
and PTFE may also be available. See
table for maximum temperature recommendations. Fluoropolymer materials are
typically used.
Testing at
Temperature
The burst pressure of each lot of Sigma EXL™ or Sigma™
Rupture Disks is tested at the users requested temperature. If the disk is
requested above or below ambient temperature, burst testing for product
certification will be carried out at this temperature to ensure the best
product accuracy. For applications with operating temperatures that may exceed
this tested burst temperature, please review with BS&B Safety Systems, Inc.
or BS&B Safety Systems Ltd.
Flow Performance - KR
Values - Rupture Disk Sizing
Flow resistance factor 'KR' may be used to determine the
relieving capacity of a system using calculations such as those described in
Crane Technical Paper No. 410. Individual KR values have been established for
both Gas and Liquid service for the Sigma EXL™ and Sigma™ disks. These are
experimentally determined at the BS&B Safety Systems Inc. flow laboratory
according to ASME procedures and witnessed by ASME representatives. Care must
be taken to use the correct value for sizing purposes. When more than one 'KR'
value is marked on the disk tag, 'KRG' is indicated for Gas service, and 'KRL'
for liquid service. A single disk tag KR value is valid for gas service only.
The KRg value is 0.38 and the KRI value is 1.25
When using KR value for sizing calculations, the nominal
pipe size (assuming schedule 40 pipe) of the vent system is used. When using
'coefficient of discharge' sizing techniques, the Minimum Net Flow Area or Net
Relief Area of the Rupture Disk (Bursting Disc) device is used.
Certification
The certification procedure for Sigma EXL™ and Sigma™ Rupture Disks exceeds those required by
standard industry Codes and Standards that require limited destructive testing
to validate burst pressure and permit acceptance of the lot with any burst test
distribution and uncentered test
data.The Sigma EXL™ and Sigma™ disk's test data is graphically presented on
their Burst Test Certificate (see picture). The curve includes 'in process' and
final certification burst test data to build a clear picture of the burst
pressure distribution. Only when the data is appropriately centered and
distributed is the lot accepted for shipment. The Certificate indicates also the burst test results of
rupture disks (bursting discs) tested from the" lot "for Quality
Department final acceptance - the quantity of test results will typically be
determined by the certification Code or Standard chosen by the user.Sigma EXL™
and Sigma™ Rupture Disks are also validated for liquid service for each lot
using a fully hydraulic burst test system and the Burst Test Certificate
endorsed accordingly.
The combination of statistical control techniques for burst
pressure, and proof pressure testing of all ordered Sigma EXL™ and Sigma™
Rupture Disks enables their application to the highest operating pressures
available from the Rupture Disk (Bursting Disc) Industry
Installation in
SRB-7RS™ Safety Head
The Sigma EXL™ and Sigma™ disks are installed in an SRB-7RS™
Safety Head permitting the correct torque to be applied in the workshop before
installation into the process. The asymmetric locating pins ensure centering
and orientation of the disk within the Safety Head. The performance-proven
metal-to-metal 'bite type' seal in the Safety Head (2"/50mm size and above)
assures a leak tight assembly. When installed properly into the SRB-7RS™ Safety
Head, the assembly can be removed, inspected, cleaned carefully then
reinstalled without replacing the disk as the pretorque capscrews maintain the
clamp load on the disk.
The SRB-7RS™ Safety Head is used with the other rupture
disks (bursting discs) (Types SKR™, S90™, JRS™, RLS™, FRS™) of the
STA-SAF® System.