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What is a Stainless Steel Flange?
A stainless steel flange is a mechanical component used to connect pipes, valves, pumps, and equipment in a piping system. Unlike threaded connections or welding alone, a flange offers a strong, reusable, and sealed connection ideal for demanding applications.
Stainless steel flanges are known for their corrosion resistance, high tensile strength, and long life in harsh environments, making them the go-to choice for industries like oil & gas, chemical, pharmaceutical, food processing, and power generation.
Why Stainless Steel Flanges Are Preferred
- Corrosion resistance in both acidic and saline environments
- Withstands high pressure and temperature variations
- Compatible with multiple piping materials (carbon steel, copper, PVC)
- Reusable and easy to install or replace
- Wide material availability: SS 304, SS 316, SS 316Ti, Alloy Steel
- Compliant with international standards like ASME SA182 and ASTM A182
Types of Stainless Steel Flanges
Understanding flange types helps in selecting the best fit for your application:
| Flange Type | Description |
|---|---|
| Weld Neck (WN) | Ideal for high-pressure systems; welded to pipe to offer strength & alignment |
| Slip-On (SO) | Easy to install; pipe slides into flange, then fillet welded |
| Blind (BL) | Used to seal pipe ends; no bore, suitable for pressure testing |
| Threaded (TH) | Screwed onto pipes; no welding needed; low-pressure use |
| Socket Weld (SW) | Pipe fits into socket; strong fillet weld ideal for small-diameter systems |
| Lap Joint (LJ) | Used with a stub-end; allows rotation and quick disassembly |
| Ring Type Joint (RTJ) | High-pressure sealing using grooved ring gaskets |
| Exhaust Flanges | Stainless steel flanges for exhaust systems, especially automotive and industrial setups |
Material Grades of SS Flanges
Flange SS 304
- Most widely used stainless steel grade
- Excellent corrosion resistance in atmospheric and freshwater environments
- Cost-effective and food-grade safe
- Applications: Water lines, food processing units, brewing and bottling plants
SS 316 Flange
- Contains molybdenum for enhanced corrosion resistance
- Performs better in saline and acidic environments
- Used in marine, chemical, and pharmaceutical industries
- Withstands chlorides and harsh industrial chemicals
SS 316Ti Flanges
- Titanium-stabilized version of SS 316
- Offers superior resistance to intergranular corrosion (from welding)
- Best for high-temperature, high-pressure applications like steam lines or pressure vessels
- Compliant with EN 1.4571 (European Grade)
Alloy Steel Flanges
- Made with Cr-Mo alloys (Chromium-Molybdenum)
- High tensile strength and thermal fatigue resistance
- Used in power plants, petrochemical refineries, and industrial processing
- Usually manufactured as per ASME SA182 Grade F1, F5, F9, F11, etc.
Class Ratings: What is a Class 150 Flange?
Class ratings define the maximum pressure-temperature a flange can withstand.
Class 150
- Rated for up to 285 psi at 100°F
- Most commonly used in water supply lines, HVAC systems, and low-pressure steam
- Available in SS 304, SS 316, and alloy steel materials
Other ratings include Class 300, 600, 900, 1500, and 2500 for progressively higher pressure applications.
150 LB Flange Sizes and Dimensions (ASME B16.5)
A sample from the ASME B16.5 standard (NPS 1/2″ to 24″):
| NPS (inches) | OD (mm) | Bolt Holes | Bolt Circle Dia | Thickness (mm) |
|---|---|---|---|---|
| 1/2″ | 89 | 4 | 60.3 | 11.2 |
| 1″ | 108 | 4 | 73.0 | 14.3 |
| 2″ | 152 | 4 | 120.6 | 17.5 |
| 4″ | 229 | 8 | 190.5 | 23.9 |
| 6″ | 279 | 8 | 241.3 | 25.4 |
| 8″ | 343 | 8 | 298.5 | 28.6 |
Always verify specific dimensions with ASME B16.5 and the flange type you select.
Flange Face Types: RF, FF, and RTJ
- RF (Raised Face) – Most common; concentrates pressure on a smaller area, improving sealing
- FF (Flat Face) – For cast iron or fiberglass piping systems; requires full-face gasket
- RTJ (Ring Type Joint) – For high-pressure and high-temperature systems using a metal ring gasket
SS Flange Bolts and Accessories
- SS Flange Bolts: Usually made from A2-70 or A4-80 grade stainless
- Gaskets: PTFE, EPDM, Spiral Wound, CAF depending on media and pressure
- Washers and Nuts: Used with flange bolts to ensure even load distribution
- Stud Bolts: Required for flange-to-flange joints, typically with two heavy hex nuts per stud
Stainless Steel Flange Applications
- Petrochemical plants
- Oil & gas pipelines
- Water treatment facilities
- Food and dairy processing
- Pharmaceutical manufacturing
- Marine and offshore platforms
- Fire protection systems
- Automotive exhausts and engine pipelines
8 Materials for Constructing Flanges
Flanges are available in various materials depending on the application, pressure, and fluid compatibility:
- Stainless Steel (SS 304, SS 316, SS 316Ti) – Excellent corrosion resistance
- Carbon Steel – High strength, low cost, suitable for oil and gas
- Alloy Steel – Added elements like Cr, Mo for high-pressure and high-temp systems
- Duplex Stainless Steel – Better corrosion resistance and strength than 316
- Copper & Brass – Common in plumbing and low-pressure systems
- PVC/UPVC – Used for non-metallic, low-pressure systems (chemical, drainage)
- Cast Iron – Used in water supply and drainage applications
- Titanium & Nickel Alloys – Used in extreme corrosive environments like marine and chemical industries
Stainless Steel Flange Specifications
Stainless steel flanges are manufactured as per the following international standards and specifications:
| Specification | Description |
|---|---|
| ASME SA182 | Forged or rolled alloy and stainless steel flanges for high-temp service |
| ASTM A182 | Standard for SS 304, SS 316, SS 316Ti, and alloy flanges |
| ASME B16.5 | Covers dimensions and pressure classes for sizes NPS ½″ to 24″ |
| EN 1092-1 | European standard for flanges and bolting |
| DIN | German flange standards (common in Europe and Asia) |
| MSS-SP44 | Steel pipe line flanges for oil and gas transmission |
| API 605 | Large-diameter carbon and stainless steel flanges |
15mm (1/2″) Stainless Steel Flanges Weight Chart
Here’s a weight estimation for 15mm (½″) stainless steel flanges under different types:
| Flange Type | Class 150 Weight (kg) | Class 300 Weight (kg) |
|---|---|---|
| Weld Neck (WN) | 1.10 | 1.60 |
| Slip-On (SO) | 0.85 | 1.30 |
| Blind (BL) | 0.95 | 1.40 |
| Socket Weld (SW) | 0.90 | 1.35 |
| Threaded (TH) | 0.80 | 1.25 |
Weights vary slightly depending on standards, tolerances, and material density.
The Manufacturing Process of Stainless Steel Flanges
1. Raw Material Selection
- Choose stainless steel billet or slab (typically SS 304/316) based on order specs.
2. Forging
- The material is heated and pressed into shape using dies and hammers, improving strength and grain structure.
3. Machining
- CNC machines cut precise flange shapes, bores, bolt holes, and faces.
4. Heat Treatment
- Normalizing or annealing removes internal stress and enhances corrosion resistance.
5. Surface Finishing
- Lathing and polishing to achieve smooth, clean surface for sealing.
6. Marking & Inspection
- Each flange is marked with grade, size, pressure rating, and standard.
- Non-destructive testing (NDT) ensures zero internal defects.
Global Export Services
We serve clients in the USA, Europe, Middle East, Southeast Asia, Africa, and Australia, offering customized stainless steel flange solutions to meet diverse industrial needs. Whether you’re looking for Class 150 stainless steel flanges, SS 304/316 flanges, or high-performance alloy steel flanges, we ensure timely delivery and competitive pricing.
Conclusion
From chemical plants to cleanrooms, stainless steel flanges are the backbone of reliable, long-lasting piping connections. Whether you’re selecting a Class 150 slip-on flange, a blind flange for steam lines, or a high-strength SS 316Ti flange for corrosive systems—understanding the materials, standards, dimensions, and applications is essential.
With this complete guide covering materials, specifications, manufacturing process, weight charts, and common queries, you’re now equipped to choose the best flange for any project.
FAQs: Stainless Steel Flange Questions
1. What are 150 lb flange sizes?
150 lb flanges are pressure-rated for 285 psi at 100°F and available from 1/2” to 24” sizes.
2. Stainless steel flange weight chart?
Flange weights vary by size and type. A 4″ Class 150 SS weld neck flange weighs approximately 9.2 kg.
3. SS 304 vs SS 316 flanges?
SS 316 contains molybdenum, making it more corrosion-resistant than SS 304, especially in marine and chemical environments.
4. Flange bolt torque chart for Class 150?
Torque ranges from 45 to 240 ft-lbs depending on flange size and gasket material.
5. How to install a stainless steel flange?
Clean surfaces, use proper gaskets, align bolt holes, tighten bolts in a crisscross pattern, and re-torque after system startup.
6. Flange face types: RF vs FF vs RTJ?
RF (Raised Face) improves sealing
FF (Flat Face) for fragile pipe materials
RTJ (Ring Type Joint) for high-pressure sealing
7. Schedule 40 vs Schedule 80 flange compatibility?
Schedule 80 pipes have thicker walls; ensure flange bore matches pipe schedule to avoid fitting gaps or stress points.
8. Stainless steel flange pressure ratings?
Common pressure classes include 150, 300, 600, 900, 1500, and 2500. Higher class = higher pressure tolerance.
9. How to identify ASME SA182 flanges?
Look for laser-marked or stamped info like grade, pressure class, heat number, and ASME code.
10. Stainless steel exhaust flanges for cars and trucks?
Made from SS 304 or SS 409, they handle extreme heat and vibration in automotive exhaust systems.
