SIGMA™ & SIGMA EXL™

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™ Rupture                                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

Sigma EXL™                                & Sigma™ Disk Specificaton
                 
                              Min/Max Pressure Rating at 72ºF (22ºC)                                PSIG (Bar)

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.

Maximum                  Recommended Temperature

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.

Minimum Net                                Flow Area (MNFA) / Net Relief Area (NRA)              

* Use MNFA in in² when sizing according                                to ASME code, simple system case.
                              + Use Net Relief Area cm² when sizing                                according to European codes

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.

SRB-7RS™                                Safety Head Specification