TOBO Stub End ASTM A403 316L DN250 PN16 EN1092-1 Type35: A Comprehensive Guide

1. Introduction

TOBO Stub Ends (also known as Lap Joint Flanges) are critical components in piping systems, enabling easy assembly and disassembly of flanged connections. The ASTM A403 316L DN250 PN16 EN1092-1 Type35 variant represents a high-performance solution designed for corrosive and high-pressure environments. This article explores its specifications, manufacturing standards, and industrial applications.

2. Material Specifications

ASTM A403 Standard

The ASTM A403 specification governs the manufacturing of wrought austenitic stainless steel pipe fittings, including seamless and welded stub ends. The 316L grade (UNS S31603) is a low-carbon variant of 316 stainless steel, offering enhanced resistance to intergranular corrosion1. Key chemical properties include:

• Chromium (Cr): 16–18%
• Nickel (Ni): 10–14%
• Molybdenum (Mo): 2–3%
• Carbon (C): ≤0.03% (max)

Mechanical Properties

• Tensile Strength: ≥485 MPa
• Yield Strength: ≥170 MPa
• Elongation: ≥40%

3. Design and Dimensional Compliance

EN1092-1 Type35 Specification

The EN1092-1 European standard defines flange dimensions and pressure ratings. The Type35 designation refers to a long-pattern stub end designed for compatibility with PN16 (16 bar pressure rating) flanges2. Key dimensional parameters for DN250 (nominal diameter 250 mm) include:

• Outer Diameter (OD): 335 mm
• Bolt Circle Diameter: 295 mm
• Number of Bolt Holes: 8 × Ø22 mm

Pressure-Temperature Ratings

• PN16 allows safe operation up to 16 bar at 120°C, with derating factors applied for higher temperatures.

4. Manufacturing Process

TOBO Stub Ends are manufactured through:

1. Forging: Hot forging of 316L billets to achieve structural integrity.
2. Heat Treatment: Solution annealing at 1,040–1,100°C followed by rapid quenching to optimize corrosion resistance.
3. Machining: Precision machining to meet EN1092-1 tolerances.
4. Surface Finish: Polished or electro-polished surfaces to reduce contamination risks in hygienic applications.

5. Corrosion Resistance and Performance

The 316L alloy excels in harsh environments due to:

• Pitting Resistance Equivalent Number (PREN): ≥25 (calculated as %Cr + 3.3×%Mo + 16×%N).
• Resistance to: Chloride-induced stress corrosion cracking (SCC), sulfuric acid, and organic acids.
• Applications in: Chemical processing, offshore oil platforms, and seawater cooling systems.

6. Industrial Applications

TOBO Stub Ends are widely used in:

1. Chemical Industry: Handling corrosive media like acids and alkalis.
2. Pharmaceuticals: Hygienic piping systems requiring smooth surfaces.
3. Oil & Gas: Subsea pipelines and refinery equipment.
4. Food Processing: Compliance with FDA and EHEDG standards.

7. Advantages Over Alternatives

• Interchangeability: Matches flange dimensions per EN1092-1, ensuring global compatibility.
• Cost Efficiency: Reduces maintenance costs by allowing flange reuse without pipe rotation.
• Durability: Superior lifespan compared to carbon steel or duplex stainless steel in chloride-rich environments.

8. Conclusion

The TOBO Stub End ASTM A403 316L DN250 PN16 EN1092-1 Type35 combines rigorous material standards, precise engineering, and robust performance. Its compliance with both ASTM and EN specifications makes it a versatile choice for industries demanding reliability under extreme operational conditions. Engineers and procurement specialists can leverage its technical merits to enhance system longevity and safety.