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MS Pipes & Fittings

Mild Steel (MS) seamless Pipe Fittings

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MS Seamless Pipe Fittings are high-pressure components used to connect seamless pipelines. Unlike ERW (welded) fittings, these are forged from solid steel billets or manufactured from seamless pipes, ensuring there is no "weak link" or weld seam. This makes them the standard choice for critical industrial systems involving steam, oil, and high-pressure fluids.

1. Primary Technical Standards

For seamless mild steel (carbon steel) fittings, two main standards are followed globally and in India:

  • ASTM A234 Grade WPB: The most common global standard for wrought carbon steel fittings for moderate and high-temperature service.

  • ASME B16.9: Governs the factory-made wrought buttwelding fittings (dimensions and tolerances).

  • IS 1239 (Part 2): The Indian standard for mild steel tubulars and other wrought steel fittings (usually up to 6" NB).

2. Common Types of Seamless Fittings

Fitting Type
Functional Detail
Seamless Elbows

Available in 45°, 90°, and 180° (Long Radius & Short Radius).

Seamless Tees

Equal Tees (same diameter) and Reducing Tees (branch is smaller).

Reducers

Concentric (symmetric) and Eccentric (used to prevent air pockets).

Caps

Used for permanent closure of the pipe end.

Stub Ends

Used in conjunction with lap joint flanges.

3. Dimensional Specification (ASTM A234 WPB / ASME B16.9)

Seamless fittings are categorized by "Schedules" to match the wall thickness of the pipe they are welded to.

Nominal Size (NB)
Outer Diameter (mm)
SCH 40 (Standard) Wall (mm)
SCH 80 (Extra Strong) Wall (mm)
1/2" (15mm)

21.3

2.77

3.73

1" (25mm)

33.4

3.38

4.55

2" (50mm)

60.3

3.91

5.54

4" (100mm)

114.3

6.02

8.56

6" (150mm)

168.3

7.11

10.97

4. Technical Material Properties

For the standard Grade WPB (the "B" refers to the minimum yield strength):

  • Chemical Composition:

    • Carbon (C): 0.30% Max

    • Manganese (Mn): 0.29% – 1.06%

    • Silicon (Si): 0.10% Min

    • Sulphur/Phosphorus: 0.05% Max each

  • Mechanical Properties:

    • Tensile Strength: 415 MPa (Min)

    • Yield Strength: 240 MPa (Min)

    • Elongation: 20% – 30%

5. Key Advantages over ERW Fittings

  • Uniform Strength: Consistent grain structure throughout the body.

  • Higher Pressure Rating: Typically rated for 20% more pressure than a welded fitting of the same material.

  • Corrosion Resistance: No weld zone means no risk of preferential "weld decay" or intergranular corrosion at the seam.

  • Better for Machining: Seamless fittings can be more easily bored or threaded without worrying about a weld line.

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