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SS Pipes & Fittings

Stainless Steel (SS) Pipe Flanges

SS FLANGES.jpg

Stainless Steel (SS) Pipe Flanges are used to create high-integrity, leak-proof connections in piping systems that require superior corrosion resistance and hygiene. Unlike MS flanges, SS flanges are used extensively in chemical plants, pharmaceutical labs, and food processing units where contamination and oxidation must be avoided.

1. Primary Technical Standards

SS flanges are manufactured to match global piping standards:

  • ASTM A182: The standard for forged or rolled alloy and stainless steel pipe flanges for high-temperature service.

  • ASME B16.5: Dimensional standard for flanges from 1/2" to 24" (Class 150 to 2500).

  • MSS SP-43: Standard for lightweight, corrosion-resistant buttwelding fittings and flanges.

  • EN 1092-1: European standard for steel flanges (PN ratings).

2. Common Material Grades

The grade of stainless steel determines the flange's resistance to specific chemicals and temperatures:

Grade
Common Name
Key Characteristics
Best Used For
SS 304/L
18/8 Stainless
High ductility, excellent corrosion resistance.
Food, dairy, and water treatment.
SS 316/L
Marine Grade
Contains 2-3% Molybdenum; resists chlorides.
Marine, chemical, and pharma.
SS 321
Titanium Stabilized
Prevents carbide precipitation at high heat.
Exhausts and heat exchangers.
SS 310S
Refractory Grade
High Chromium/Nickel for heat resistance.
Kilns, furnaces, and boiler parts.

3. Technical Parameters (ASME B16.5)

Flanges are categorized by their pressure-temperature rating, known as "Class."

  • Pressure Ratings: Class 150, 300, 400, 600, 900, 1500, and 2500.

  • Facing Types: * Flat Face (FF): For low-pressure systems.

    • Raised Face (RF): Most common; concentrates pressure on the gasket.

    • Ring Type Joint (RTJ): Uses a metal ring for extremely high pressures.

4. Dimensional Data (Class 150 - Standard)

The dimensions of an SS flange must precisely match the bolt-hole pattern of the equipment it connects to.

Nominal Size (NB)
Outside Dia (mm)
Thickness (mm) Copy
No of Holes
Bolt Circle Dia (mm) Copy
1/2" (15mm)
88.9
11.1
4
60.3
1" (25mm)
108.0
14.3
4
79.4
2" (50mm)
152.4
19.1
4
120.7
4" (100mm)
228.6
23.9
8
190.5
6" (150mm)
279.4
25.4
8
241.3

5. Surface Finishes

In the stainless steel industry, the finish is as important as the grade:

  1. Stock Finish: A continuous spiral groove (phonographic finish) for general industrial use.

  2. Smooth Finish: Used with metal gaskets.

  3. Mirror Polished: High-shine finish used in architectural and sanitary (food/pharma) applications.

  4. Serrated: Concentric or spiral grooves to "bite" into the gasket for a better seal.

6. Essential Quality Tests

  • Positive Material Identification (PMI): To verify the exact chemical composition (e.g., ensuring 316 actually contains Molybdenum).

  • Solution Annealing: Heating to 1000°C+ and quenching to ensure maximum corrosion resistance.

  • Dye Penetrant Test (DP): Checking for surface cracks or porosity in the forged body.

  • IGC Test: Testing for Intergranular Corrosion to ensure the flange won't fail at the weld zone.

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