Flange Standards & Codes – ASA 150, ANSI & Stainless Flanges
Flange Standards & Codes – ASA 150, ANSI & Stainless Flanges Explained
When you're sourcing pipe flanges for any industrial application, understanding standards like ASA 150, ANSI flange classes, and stainless pipe flange specifications is essential. These standards ensure compatibility, pressure rating accuracy, and safety — especially in oil & gas, water pipelines, HVAC, or chemical industries.
In this guide, we break down the most important flange codes and standards you’ll encounter in India and globally — so you can buy, inspect, and install with confidence.
What Are Flange Standards and Why Do They Matter?
Flange standards define the physical dimensions, pressure-temperature ratings, materials, and testing criteria of a flange. Following a standard ensures:
- Seamless interchangeability across brands and suppliers
- Safety under pressure or heat
- Regulatory compliance (e.g., ANSI/ASME in the U.S., IS/BS in India/U.K.)
- Streamlined procurement and design
Flanges that look the same can be drastically different in dimensions and performance if made to different standards.
ASA 150 Flange – The Most Used Standard in India
ASA 150 refers to American Standard Association flanges with a pressure rating of 150 PSI (10 bar). This is one of the most widely used classes for water, HVAC, and non-critical systems.
ASA 150 Flange Key Specs:
- Pressure Rating: 150 PSI (~10 bar)
- Drilling Pattern: Matches ANSI B16.5 Class 150
- Material Options: MS, SS304, SS316, Cast Iron
- Size Range: ½” to 24” (DN15–DN600)
- Face Type: Raised Face (RF), Flat Face (FF)
Use Case:
Ideal for low-pressure water pipelines, HVAC systems, and process plants where extreme pressure is not a concern.
Learn more: ASA 150 Flange Standard →
ANSI Flange Standards – Global Compatibility for Precision Fit
ANSI (American National Standards Institute) defines specifications under the ASME B16.5 and B16.47 standards — widely adopted across the world, especially in oil & gas, petrochemical, and marine sectors.
ANSI Flange Classes:
- Class 150
- Class 300
- Class 600
- Class 900
- Class 1500
- Class 2500
Each class supports higher pressure and temperature ratings.
ANSI Flange Covers:
- Bolt circle diameters
- Bolt hole counts
- Gasket seating surfaces
- Face finish (e.g., serrated)
Important: ANSI 150 = ASA 150
(They are functionally interchangeable, though ASA is an older term.)
Read the full breakdown: ANSI Flange Specifications →
Stainless Pipe Flanges – Grades & Performance
Stainless steel flanges are a popular choice in corrosive, high-pressure, and hygiene-sensitive environments like food, pharma, marine, and chemical plants.
Common SS Flange Grades:
| Grade | Composition | Best Used For |
|---|---|---|
| SS 304 | 18% Cr / 8% Ni | General purpose, low corrosion |
| SS 316 | 16% Cr / 10% Ni / 2% Mo | Marine, chemical, pharma |
| SS 321 | 304 + Titanium | High-temperature pipelines |
Surface Finish Options:
- Mirror polish (for hygiene industries)
- Machined face
- Serrated finish for gasket grip
Types of SS Flanges:
- Weld neck
- Slip-on
- Blind
- Lap joint
- Threaded
- Socket weld
Explore all grades here: Stainless Pipe Flange Grades →
Comparison Table – ASA vs ANSI vs SS Flanges
| Feature | ASA 150 Flange | ANSI Flange | Stainless Flange |
|---|---|---|---|
| Pressure Rating | 150 PSI | 150–2500 PSI | 150–1500 PSI |
| Standard Code | ASA B16.5 (old term) | ANSI/ASME B16.5/B16.47 | Material-focused (304/316) |
| Material Flexibility | Mostly MS or SS | MS, SS, Cast, Alloy | Stainless steel grades |
| Surface Type | RF / FF | RF / FF / RTJ | RF / FF / Polished |
| Corrosion Resistance | Moderate | Depends on material | High |
Buyer Checklist for Flange Standards
- ✅ Pipe Size (NB or DN)
- ✅ Pressure Rating (Class 150/300/600...)
- ✅ Flange Type (Weld Neck, Blind, etc.)
- ✅ Standard Code (ASA / ANSI)
- ✅ Material (MS, SS304, SS316)
- ✅ Gasket Type (if included)
- ✅ Test Certificate / IS Mark
FAQ – Pipe Flange Standards
Q1. Is ASA 150 same as ANSI 150?
Yes. ASA 150 is the older name for ANSI Class 150. Both follow the same dimensions.
Q2. What is the meaning of Class 150 in flanges?
It refers to the pressure rating – 150 PSI max operating pressure at a reference temperature.
Q3. What is ASME B16.5?
It’s the ANSI/ASME standard covering flange dimensions, pressure classes, materials, and testing.
Q4. Which stainless flange is best for chemical use?
SS316 flanges offer superior corrosion resistance due to their molybdenum content.
Q5. Do I need ANSI standard flanges in India?
Yes, if your project follows global engineering standards or uses imported equipment.
Conclusion
Flange standards like ASA 150, ANSI, and SS flange grades give engineers and buyers a common language for safe, reliable pipeline connections. Understanding these standards isn't just technical — it's essential for long-term performance and leak-proof results.
Before buying, double-check the specs, pressure class, and material to ensure compatibility.
Looking for standard-compliant pipe flanges at the best rates?
Get Verified ASA, ANSI & SS Flanges – Contact Udhhyog Now →
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