Flanged Connection • Industrial Safety Relief Valves
Flanged Safety Valves Manufacturer for Steam, Vessels and Process Systems
Flanged safety valves are pressure relief valves with bolted flange connections for boilers, pressure vessels, steam headers, compressors, reactors, storage tanks, chemical process lines and skid-mounted systems. They are often specified as flanged safety relief valves, flanged pressure relief valves, flanged PSVs or safety valves with ASME, EN, DIN or JIS flange connections.
ZOBAI supplies flanged safety valves with engineering support for set pressure, certified relieving capacity, inlet and outlet flange size, flange class, facing type, body material, seat material, discharge condition, back pressure and project documentation.
Connection: ASME / EN / DIN / JIS Flange
Facing: RF / FF / RTJ
Classes: 150 / 300 / 600 / 900 / 1500 / 2500
Service: Steam / Gas / Vapor / Liquid / Chemical Media
Key Checks: Set Pressure / Capacity / Flange Rating / Back Pressure
Docs: Datasheet / Test Report / Calibration Record / Material Certificate
Flanged safety valve selection should be confirmed against the actual medium, set pressure, operating pressure, required relieving capacity, temperature, inlet flange, outlet flange, facing type, gasket, material, discharge system and applicable code requirements.
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Flanged Safety Valves for Industrial Pressure Relief Systems
Flanged safety valves are pressure relief valves with flanged inlet or outlet connections, commonly used on pressure vessels, boilers, steam headers, compressors, reactors, storage tanks, chemical process lines and skid-mounted systems where bolted flange connections are required for strength, alignment, maintenance and code compliance.
Why flange selection matters
A flanged safety valve is not selected only by nominal pipe size. The flange standard, pressure class, facing type, gasket, bolt load, material, set pressure, required relieving capacity, medium, temperature and discharge piping all affect whether the valve can protect the equipment correctly.
A buyer may request a safety valve flange size or a flanged safety relief valve, but the flange connection is only one part of the specification. The valve must still be checked by orifice area, certified relieving capacity, back pressure, inlet pressure loss, seat material and applicable project standard.
Selection boundary
Flanged safety valves are usually selected for larger lines, higher relieving capacity, regulated pressure equipment, high temperature service, steam systems, process plants and applications where the valve must be removed for inspection or recalibration without damaging threaded connections.
A 2-inch, 3-inch or 4-inch flanged valve still needs capacity verification. The nominal flange size does not prove that the valve can relieve the required flow during the overpressure case.
How a Flanged Safety Valve Works
A flanged safety valve works like other safety relief valves: the disc remains closed during normal operation and opens automatically when system pressure reaches the set pressure. The flanged connection provides a bolted pressure boundary between the valve and piping. Correct flange rating, gasket selection, bolt tightening and piping alignment are essential for safe installation.
Normal Operation
The valve remains closed below set pressure. The flange joint must remain tight under operating pressure and temperature.
Pressure Reaches Set Point
When inlet pressure reaches set pressure, the disc lifts and the valve begins to relieve the protected system.
Relieving Flow
The valve must discharge the required capacity through the selected orifice and outlet flange arrangement.
Reseating
As pressure falls, the valve reseats. Outlet back pressure, pipe stress and seat condition can affect reseating behavior.
Key Flange Details to Confirm Before Ordering
Flanged safety valve selection must match both pressure relief performance and piping connection requirements. The flange is part of the pressure boundary, so the rating, facing, gasket and bolt arrangement need to be confirmed before production.
ASME, EN, DIN, JIS or Project Flange Standard
Flanged safety valves may be specified with ASME B16.5, ASME B16.47, EN 1092, DIN, JIS or project-specific flange requirements. These standards define different dimensions, bolt patterns, pressure-temperature ratings and facing details.
For replacement projects, buyers should provide the existing valve nameplate, flange standard, inlet size, outlet size, pressure class, facing type and photos of the flange connection.
Flange Pressure Class
Flange class, such as Class 150, 300, 600, 900, 1500 or 2500, is not the same as valve set pressure. The allowable pressure depends on material and temperature. A high set pressure or high temperature application must check both valve rating and flange pressure-temperature limit.
Do not select a flanged safety valve only by “same flange size.” Size, class, material group and temperature must be reviewed together.
RF, FF and RTJ Facing
Raised face, flat face and ring type joint flange facings require different gasket and mating flange arrangements. Mismatched flange facing can cause leakage, gasket damage or unsafe bolting conditions.
RTJ facing is often used in higher pressure or more severe service, while RF is common in many industrial piping systems. The final choice should follow project piping specification.
Gasket, Bolting and Flange Seal Material
Gasket material must be compatible with pressure, temperature, medium and flange facing. Bolt material and tightening method affect gasket compression and long-term sealing reliability.
For special requirements such as helium leak rate, the flange seal material, gasket design, surface finish, bolt load and test method must be stated clearly in the RFQ.
Quick Flanged Safety Valve Fit Check
Use this quick guide to identify what should be reviewed before ordering. It does not replace sizing calculation, flange rating verification or project code review.
Select your main service condition
Click one condition below to see the engineering checks that matter most.
Parameters That Decide Whether a Flanged Safety Valve Is Suitable
Flanged Safety Valve vs Threaded Safety Valve
| Item | Flanged Safety Valve | Threaded Safety Valve |
|---|---|---|
| Connection | Bolted flange connection such as ASME, EN, DIN or JIS. | Screwed connection such as NPT, BSP, G or Rc. |
| Best for | Pressure vessels, steam systems, process plants, high flow and regulated equipment. | Compact skids, compressors, air receivers, water systems and small equipment. |
| Maintenance | Easier removal and reinstallation with controlled gasket replacement. | Compact but thread damage can complicate repeated replacement. |
| Installation risk | Wrong flange class, facing mismatch, gasket issue, bolt load or pipe alignment. | Wrong thread standard, sealant contamination, cross-threading or over-tightening. |
| Typical capacity | Often selected for medium to large relieving capacity duties. | Often selected for smaller or compact relief duties. |
| Selection focus | Flange standard, class, facing, capacity, back pressure and materials. | Thread standard, size, set pressure, medium and installation torque. |
Where Flanged Safety Valves Are Used
Steam systems and boilers
Flanged safety valves are commonly used in steam service where temperature, relieving capacity, discharge reaction force and inspection access are important. Steam applications should confirm seat material, lever requirement, blowdown and outlet piping.
Pressure vessels and reactors
Pressure vessels, reactors and separators often require flanged safety relief valves selected by credible overpressure case, set pressure, certified capacity, vessel MAWP, flange class and documentation requirements.
Petrochemical and chemical process lines
Chemical and petrochemical services may require carbon steel, stainless steel or alloy materials, bellows balancing, RTJ facing, corrosion-resistant trim or project-specific gasket and bolting requirements.
Common discharge and flare headers
When flanged safety valves discharge into a header, back pressure and outlet resistance must be reviewed. The outlet flange size alone cannot confirm stable opening or certified relieving capacity under actual discharge conditions.
Flanged Safety Valve Selection Table
| Service Condition | Common Requirement | Recommended Review | Key Engineering Check | Main Risk |
|---|---|---|---|---|
| Steam service | Reliable high-temperature pressure relief | Flanged steam safety valve | Steam capacity, set pressure, seat design, flange class and discharge force | Wrong capacity or unsafe steam discharge |
| Pressure vessel | Code-related overpressure protection | Flanged safety relief valve | MAWP, set pressure, certified capacity and flange rating | Selecting by nozzle size instead of relief case |
| Process gas | Leakage control and capacity verification | Soft seat or metal seat flanged safety valve | Seat material, leakage class, temperature and medium compatibility | Seat leakage or wrong seal material |
| Common discharge header | Stable relief into outlet system | Bellows balanced or pilot operated flanged valve | Superimposed and built-up back pressure | Chatter, reduced capacity or poor reseating |
| High pressure service | Higher flange class and robust sealing | Class 600 / 900 / 1500 / 2500 as required | Pressure-temperature rating, RTJ option, gasket and bolting | Flange class mismatch or gasket failure |
| Replacement project | Match existing installation safely | Nameplate and drawing verification | Flange standard, class, facing, orifice, capacity and material | Replacing by flange size only |
This table is for preliminary engineering screening. Final selection must be confirmed against medium, set pressure, operating pressure, required relieving capacity, flange standard, pressure class, facing type, gasket, material, temperature, back pressure and applicable code requirements.
Common Engineering Mistakes to Avoid
Matching flange size but not flange class
Two valves may have the same inlet flange size but different pressure classes, facing types and material ratings. A replacement valve should match the piping specification and pressure-temperature requirement, not only the nominal size.
Selecting by vessel nozzle size
A vessel nozzle or safety valve flange size does not prove the valve can relieve the required flow. The relieving case, orifice area and certified capacity must be checked before confirming the model.
Ignoring pipe alignment and bolt load
Flanged valves can leak or distort if piping alignment is poor or bolt load is uneven. Installation should avoid excessive external loads on the valve body and maintain the correct gasket compression.
Flanged Safety Valve Troubleshooting Table
| Symptom | Possible Cause | Engineering Check | Corrective Action |
|---|---|---|---|
| Leakage at flange joint | Wrong gasket, facing mismatch, uneven bolting, damaged flange face or pipe stress | Check flange standard, facing type, gasket material, bolt load and alignment | Replace gasket, correct bolting procedure and realign piping |
| Valve chatters during relief | Oversizing, excessive inlet loss, high outlet back pressure or unstable flow | Review inlet piping, outlet header, valve size and actual relief flow | Recalculate sizing and piping loss, then review valve configuration |
| Valve leaks from seat | Damaged seat, dirt, operating pressure too close to set pressure or thermal distortion | Inspect seat, operating margin, medium cleanliness and temperature cycling | Clean, repair, retest or review seat material and operating margin |
| Wrong flange fit during installation | Incorrect ASME/EN/JIS standard, class, facing or bolt pattern | Compare drawing, flange standard, bolt circle and facing type | Replace with correct flange specification before installation |
| Helium leak test fails | Incorrect seal material, gasket surface issue, flange finish, seat leakage or test boundary mismatch | Confirm test method, acceptance limit, seal material, gasket and leakage path | Define test scope clearly and select compatible sealing materials |
Standards and Documents to Confirm Before Purchase
Standards to review
Flanged safety valve specifications may reference pressure relief valve standards, flange standards, material standards and project-specific equipment requirements. The correct requirements depend on protected equipment, medium, pressure, temperature and buyer specification.
- ASME B16.5 or project flange standard for flange dimensions, pressure-temperature rating and facing requirements.
- API 526 where flanged steel pressure relief valve dimensions, orifice designation and pressure class are relevant.
- API 520 for sizing, selection and installation guidance where applicable.
- API 527 when seat tightness testing is specified.
- ASME BPVC or local pressure equipment code where boiler or pressure vessel protection applies.
- Project-specific gasket, bolting, helium leak rate or material documentation requirements.
Documents buyers often request
Documentation should be confirmed before quotation, especially for pressure vessels, boilers, steam systems, petrochemical plants, LNG/LPG skids and regulated equipment.
- Valve datasheet and model specification.
- Inlet and outlet flange standard, class and facing type.
- Set pressure calibration record.
- Certified relieving capacity information.
- Pressure test report and seat tightness report when required.
- Material certificate and heat number traceability where specified.
- Nameplate, tagging, gasket and bolting requirements when applicable.
RFQ Checklist for Flanged Safety Valves
| Required Data | Why It Matters | Example Input |
|---|---|---|
| Medium | Determines sizing method, material and seat design. | Steam, air, nitrogen, natural gas, water, chemical vapor |
| Set pressure | Defines the valve opening point. | 10 bar g, 150 psi, 600 psi |
| Operating pressure | Confirms operating margin and leakage risk. | 80% of set pressure or project value |
| Required relieving capacity | Confirms whether the valve can protect the equipment. | kg/h, lb/h, Nm³/h, SCFM, GPM |
| Inlet flange | Defines installation interface and pressure rating. | ASME B16.5 2 inch Class 300 RF |
| Outlet flange | Confirms discharge connection and back pressure review. | ASME B16.5 3 inch Class 150 RF |
| Facing type | Determines gasket and mating flange compatibility. | RF, FF, RTJ |
| Temperature | Affects flange rating, material and seat selection. | 180°C, 400°C, ambient |
| Material requirement | Prevents corrosion and pressure-temperature mismatch. | WCB, CF8M, WC6, WC9, alloy option |
| Seat or seal material | Affects leakage, helium test and temperature limit. | Metal seat, PTFE, FKM, EPDM, project specified |
| Applicable code | Defines testing, documentation and acceptance requirements. | ASME, API, ISO, EN, GB, project specification |
| Existing drawing or nameplate | Reduces replacement selection risk. | Photo, datasheet, model number, flange details |
Need Help Selecting a Flanged Safety Valve?
Send us your medium, set pressure, operating pressure, relieving capacity, inlet flange, outlet flange, facing type, temperature, material requirement and existing datasheet. Our engineering team can review whether a flanged safety valve or flanged safety relief valve is suitable before quotation.
Prepare these data before RFQ
TECHNICAL INSIGHTS
Insights for Safer Valve Selection
FAQ
Flanged Safety Valve FAQs for Flange Size, Pressure Class and Selection
What is a flanged safety valve?
A flanged safety valve is a pressure relief valve with bolted flange connections. It opens automatically when system pressure reaches the set pressure and relieves excess pressure from boilers, pressure vessels, steam systems, process equipment or discharge headers.
What is a flanged safety relief valve?
A flanged safety relief valve is a safety relief valve with flanged inlet or outlet connections. It is usually selected for industrial pressure equipment where bolted flange connections are required for strength, maintenance access, pressure rating or project piping standards.
Is safety valve flange size enough to select a valve?
No. Safety valve flange size only confirms the piping interface. The valve must also be selected by set pressure, required relieving capacity, orifice area, medium, temperature, flange class, facing type, material, back pressure and applicable code requirements.
What flange standards are used for flanged safety valves?
Common flange standards include ASME B16.5, ASME B16.47, EN 1092, DIN and JIS. The required standard depends on the project piping specification, country or region, pressure class, size range and mating flange design.
Can a flanged safety valve be used in steam service?
Yes. Flanged safety valves are commonly used in steam service, but selection should confirm steam capacity, set pressure, temperature, body material, seat design, flange class, discharge reaction force, outlet piping and whether a lever or specific bonnet design is required.
What is a flanged angle safety valve?
A flanged angle safety valve has an inlet and outlet arranged in an angle configuration, usually for specific piping layouts or discharge directions. Buyers should confirm inlet and outlet flange orientation, center-to-face dimensions, installation space and discharge piping loads.
What does flanged safety valve symbol mean on a P&ID?
A flanged safety valve symbol on a P&ID usually indicates a safety or pressure relief valve installed with flanged piping connections. The symbol alone does not define set pressure, capacity, flange class, facing type or valve construction, so the datasheet should be checked.
What does flanged safety valve symbol mean on a P&ID?
Provide the medium, set pressure, operating pressure, required relieving capacity, temperature, inlet flange, outlet flange, facing type, material requirement, seat or seal material, back pressure condition, applicable code, quantity and any existing drawing or nameplate.
What information should I provide before requesting a quotation?
Provide the medium, set pressure, operating pressure, relieving capacity, relieving temperature, inlet and outlet size, connection standard, material requirement, back pressure condition, applicable code, quantity and any existing drawing or datasheet.
Raymon Yu
“When a safety valve fails to pop on site, it’s rarely because someone can’t read a standard. It’s usually because critical operating parameters (like backpressure or relief temperature) were assumed instead of specified. I reviewed the key technical content on this page to keep it practical, API/ASME spec-aligned, and RFQ-ready. (We prefer assumptions for lunch choices.)”
What I work on daily: reviewing drawings and project specs, supporting engineer-to-engineer questions, resolving capacity calculations, material selection, and backpressure impacts so production and quoting stay consistent. (Yes—set pressure and seat tightness test records get plenty of attention.)