BS&B The STA-SAF System

The Sta-Saf system combines six Rupture Disk (Bursting Disc) types and three safety head options that provide the user with extended service life reverse buckling disk technology in sizes from 1"/25mm to 36"/900mm at burst pressures ranging from 5 psi/0.34 bar to 2000 psi/137.9 bar.
This catalog describes the types JRS™, S-90™, RLS™, and FRS™ Rupture Disks and their Safety Head (holder) options. The most extensive size and set pressure capability is offered through these widely applied designs that are in service in well over 50,000 installations worldwide.
The most capable Sta-Saf technologies, SKR™ & Sigma™ Rupture Disks, have their own dedicated catalogs (77-4003 and 77-4011 respectively).

Standard Features of the

STA-SAF® Family

STA-SAF® Rupture Disks:

90% or greater operating ratio
Vacuum resistant
Solid metal construction enabling optimum leak tightness
Designed for non-fragmentation
Recommended for isolation of pressure relief valves
Metal tag with product identification and traceability data, as well as code symbol stamps as appropriate

STA-SAF® Safety Heads:

Disk dome shielded by safety head inlet for all sizes
Locating pins ensure centering and correct orientation of the disk within the safety head
“Bite-type” seal for sizes 2”/50mm and larger to optimize leak tightness when appropriately installed
Flow arrow to indicate direction of flow after installation
Optional tell-tale connection in safety head outlet
Spiral groove with 125-250 AARH finish on both inlet and outlet safety head external mating surfaces to enhance gasket performance

For each material the upper temperature limit has been determined from the recommendations of material manufacturers and user experience. Rupture disk technology uses Nickel and its alloys to provide the user with a range of excellent corrosion resistance, and thermal stability particularly in the case of alloy 600.
Hastelloy is a trademark of Haynes International Inc., Monel and Inconel are trademarks of Inco Alloys International, Inc. BS&B may use equivalent materials from other sources.
Fluoropolymer film liners are available as an additional corrosion barrier with most Sta-Saf Rupture Disks. Order as "TEF LINER" when required. Liners are applied to the inlet/process side of the Rupture Disk, unless otherwise agreed.
Fluoropolymer materials are typically used (for example FEP, PFA, PTFE).
This wide material range provides the user with options in the selection of a Rupture Disk (Bursting Disc) material that is resistant to the process media. Corrosion of disk material will affect performance and may result in premature burst or leakage through the disk.

Operating Pressure Ratio

Sta-Saf reverse buckling Rupture Disks can be operated to 90% of their marked burst pressure (or to 95% of their minimum burst pressure) for burst pressures of 40 psi (2.76 bar) and higher.
For lower burst pressures, the operating pressure ratio is 90% of minimum burst pressure. For applications that demand a closer relationship between operating pressure and burst pressure, select type Sigma EXL™ (see catalog 77-4011) which can operate up to 100% of minimum burst pressure.

Differential Pressure

Rupture disks respond to differential pressure. Please take into account the service conditions at the inlet and outlet of a Rupture Disk (Bursting Disc) when completing specifications.

Burst Pressure Tolerances

All of the Sta-Saf Rupture Disks offer the same tolerance considerations when completing a specification. Whether the ASME/North American or European/ISO approach to burst pressure and tolerance is used, BS&B applies both a burst tolerance and an optional manufacturing design range.
Burst tolerance is the +/- range of pressure over which a Rupture Disk (Bursting Disc) can be expected to burst. Burst tolerance is either +/-5% of burst pressure or +/- 2 psi (+/-0.138 bar) for disks rated below 40 psi (2.76 bar).

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Manufacturing design range is a range of pressure, always applied to the minus side of the user requested burst pressure for Sta-Saf Rupture Disks, that simplifies disk fabrication testing and provides economic benefit to the user where such an added tolerance can be accommodated by the application.
Manufacturing Design Range (MDR) choices are provided for all Sta-Saf Rupture Disks:
MDR= 0: where the user requires the tightest margin between normal service pressure and burst pressure, a zero range disk shall be used.
MDR= -5%: applied to the requested burst pressure, a -5% range allows an additional 5% tolerance applied on the minus side of the user requested burst pressure.
MDR= -10%: applied to the requested burst pressure, a -10% range allows an additional 10% tolerance applied on the minus side of the user requested burst pressure.
Note: MDR and burst tolerance are additive. In the European/ISO case, the burst tolerance and MDR are simply combined. In the ASME case, the 'marked burst pressure' for a lot of Rupture Disks must be a value within the agreed manufacturing design range and then the burst tolerance is applied.

The two-step approach to set pressure specification:

1. Decide between ASME/North American (with or without 'UD' stamp) and European (with or without 'CE' mark) / ISO standards.
2. Select the manufacturing design range appropriate to the application and check that it is available for the disk type selected.
(0, -5 or -10%)

Pressure/Temperature Relationship

The burst pressure of all Rupture Disks is partially determined by the physical properties of the material employed. Tensile strength will vary with temperature, which leads to variation in burst pressure. Reverse buckling technology is the least sensitive to temperature variations and is used by all Sta-Saf Rupture Disks. However, for the highest accuracy of performance, BS&B certifies Sta-Saf Rupture Disks by testing at the users’ chosen burst temperature.
Where operating pressure and temperature may rise rapidly, the user should carefully select the temperature of the Rupture Disk (Bursting Disc). BS&B can provide advice for such applications. Inconel (alloy 600) provides excellent thermal stability for applications that experience a wide range of service temperatures at which over-pressure might occur.
The burst pressure of each lot of Sta-Saf Rupture Disks is tested at the users specified temperature (burst temperature). Should the disk be rated above or below ambient temperature, burst testing for product certification shall be conducted at this coincident burst temperature to ensure the best product accuracy. For applications which have operating temperatures that may exceed the burst temperature, please review with BS&B Safety Systems, Inc. or BS&B Safety Systems, Ltd.

KR: Flow Resistance Factor

Flow resistance factor "KR" may be used to determine the relieving capacity of a system when using techniques such as those described in Crane Technical Paper No. 410.
Individual KR values have been established for both gas & liquid service, where appropriate, for Sta-Saf Rupture Disks. Care must be taken to use the correct value for sizing purposes.
When KR values are marked on Sta-Saf Rupture Disk (Bursting Disc) tags, those for gas service are shown as KRg or KR (GAS), and those for liquid service are shown as KRl or KR (LIQ). 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 (MNFA) or Net Relief Area (NRA) of the Rupture Disk (Bursting Disc) device is used.
The S-90 Rupture Disk (Bursting Disc) manufactured from Inconel (alloy 600) material has the lowest available "KRg" value of 0.232. KR.
You can obtain MNFA and NRA values at our website at www.bsbsystems.com or from our sales representatives and distributors.

Installation

The Sta-Saf family of Rupture Disk (Bursting Disc) devices is designed for installation between pipe flanges. Compatibility with all international flange standards is available, including: ANSI, DIN, JIS, BS, ISO, AFNOR and UNI. Between the Safety Head and the pipe flanges an application compatible gasket is used for sealing purposes.
The unique configuration of the SRB-7RS Safety Head design enables the same holder to be installed between flanges covering a range of flange specifications. For example: a single design of 1"/25mm SRB-7RS Safety Head is compatible with ANSI 150/300/600, DIN PN10/16/25/40, and JIS PN10/16/20/30/40 flanges. This will reduce the inventory of Safety Heads required by the user, and provide simplicity of common installation practices.

Code Compliance

The Sta-Saf family of products is designed to meet the requirements of the international Rupture Disk (Bursting Disc) standards.
Certification to the following codes is available:
ASME Section VIII (including 'UD' stamp) and Section III
CEN ISO 4126 part2 (pending); ‘CE’ Mark
ISO 6718, BS2915, SVTI, Stoomwezen
TUV AD Merkblatt A1
The Sta-Saf family of Rupture Disk (Bursting Disc) devices is compliant with API RP520 Part 1 recommendations.

Double Disk Assemblies

Double disk assemblies consist of three flange components, an inlet, a mid-flange and an outlet flange with a second disk between the mid-flange and outlet flange. The SRB-7RS Safety Head and the S90-7R Safety Head are available as double disk assemblies.
Applications:
1. Prevention of leakage of corrosive, toxic or expensive process materials and disk service life extension in continuous processes. The first disk isolates and protects the second disk from a corrosive process medium. Leakage caused by fatigue or corrosion through the first disk will be prevented from escaping by the second disk. Maintenance replacement can be through a planned shutdown. (Use of a tell-tale assembly between the two Rupture Disks is required.)
2. Elimination of back pressure - the second Rupture Disk (Bursting Disc) withstands the system back pressure, isolating the first disk. Any change in pressure differential across the first disk induced by back pressure is eliminated and it will rupture at its rated burst pressure. (The second Rupture Disk (Bursting Disc) may be rated at a lower burst pressure to compensate for the maximum back pressure that may coincide with a burst condition).
3. Quick Opening Valve. The volume between the two disks is pressurized. The evacuation of this pressure causes both disks to rupture virtually simultaneously providing an immediate full relief opening when the inlet pressure exceeds the disk burst pressure.

S-90™ Precision Cross-Scored

Reverse Buckling Rupture Disk (Bursting Disc)

The S-90 is a domed, solid metal, precision scored reverse buckling disk, which, upon over-pressure, reverses and opens along pre-weakened cross-score lines to provide a full relief opening.
The compression loaded S-90 disk offers an extended service life under pressure cycling conditions compared to a conventional tension loaded disk. The S-90 disk exhibits excellent fatigue resistance in cyclic pressure service, surviving 1,000,000 pressure cycles from 0-90% of its marked burst pressure.
Designed for non-fragmentation
Withstands full vacuum and back pressure equal to or less than burst pressure (higher upon request)
Suitable for operating pressure to 90% of the marked burst pressure and 95% of the minimum burst pressure (CEN ISO 4126-2 standard pending)
Gas service (acceptable for liquid service with a compressible gas/vapor pocket between the liquid and disk)
Damage safety ratio 1.5. An S-90 disk damaged or installed incorrectly will burst at or below 1.5 times its marked burst pressure
Reversal safety ratio equal to or less than 1.5. An S-90 disk and Safety Head installed upside down in the pressure system will burst at 1.5 times its marked burst pressure or less
Optimum fatigue resistance in pressure pulsating or cycling conditions
Ideal for safety relief valve isolation
Inconel material has the lowest published KR (Gas) of 0.232
Optional TEF liners to enhance corrosion resistance (on the inlet/process and/or down-stream side of the disk). Order as “TEF Liner” or identify special material requirements

*30” and 36” to fit MSS SP-44 Class 150 flanges.

SRB-7FS™ Pre-Torqued Safety Head

Full-bolted option sharing the design features of the type SRB-7RS Safety Head. The type SRB-7FS Safety Head installs between companion flanges with the studs passing through bolt holes in the perimeter of the holder.
Recommended for RTJ, tongue and groove flange facings, or for a Safety Head in Nickel Alloy 200 or Tantalum (above 1 1/2", 40mm size).
Standard Materials: 316 Stainless Steel and Carbon Steel. Also available in Nickel Alloy 200 and Tantalum.
Products, specifications and all data in this literature are subject to change without notice. Questions regarding product selection and specifications for specific applications should be directed to BS&B Safety Systems, Inc. or BS&B Safety Systems Ltd.
All sales are subject to BS&B Safety Systems, Inc. or BS&B Safety Systems, Ltd. standard terms and conditions of sale. Nothing herein should be construed as a warranty of merchantability or fitness for a particular purpose.