A large diameter flange (also known as large size flange) is a crucial component in modern industrial piping systems, widely used in oil and gas, petrochemical, power generation, and offshore industries.
Designed and manufactured according to international standards such as ASME B16.47, EN 1092-1, and GB/T 9119, large flanges provide high strength, excellent sealing performance, and superior corrosion resistance.
They are essential for connecting large pipelines, pressure vessels, and heat exchangers, ensuring long-term safety and reliability under extreme temperature and pressure conditions.
What Is a Large Diameter Flange?
In industrial standards, a large diameter flange generally refers to a flange with a nominal diameter of:
- DN ≥ 600mm (24”) according to ASME standards
- DN ≥ 700mm under EN or GB standards
Compared with standard flanges, large flanges have greater thickness, more bolt holes, and higher pressure ratings, allowing them to withstand heavy loads and cyclic thermal stresses.
They are mainly standardized under ASME B16.47 Series A and B, which specifically cover flanges larger than 24 inches.
Common Types of Large Diameter Flanges
Vorschweißflansch (WN)
Features a long tapered neck welded to the pipe end. Strong structure with excellent sealing performance; ideal for high-temperature and high-pressure systems.
Slip On Flange (SO)
The pipe is inserted into the flange and then welded. Easy to align and install; commonly used in medium and low-pressure pipelines.
Blind Flange (BL)
No center bore; used to close the ends of pipes or equipment openings. Convenient for maintenance and pressure testing.
Lap Joint Flange (LJ)
Consists of a stub end and a loose backing ring that can rotate freely. Suitable for lined or frequently dismantled pipelines.
Integral Flange (IF)
Forged or cast as part of a valve or equipment body. No welding seam, very strong, and used in high-stress applications.
Threaded Flange (TH)
Connected through internal threads without welding. Ideal for low-pressure systems where welding is not suitable.
Advantages and Limitations
Vorteile
- Strong and reliable connection
- Excellent sealing and reusability
- High interchangeability (standardized design)
- Suitable for harsh, high-temperature, and high-pressure conditions
Einschränkungen
- Heavy weight and complex installation
- High manufacturing cost
- Requires precise alignment and bolt tightening
- Not ideal for lightweight or compact systems
Manufacturing Process of Large Flanges
The manufacturing of large flanges involves multiple precise and controlled steps:
a. Material Selection
- Carbon Steel: A105, Q235B – for general pressure systems
- Stainless Steel: 304, 316L – for chemical and food industries
- Alloy Steel: F11, F22, F91 – for high-temperature systems
- Duplex & Nickel Alloys: 2205, C276, Inconel 625 – for marine or corrosive environments
All materials are supplied as forged rings or billets with EN 10204 3.1 certification.
b. Forging & Ring Rolling
- Heating billets to 1100–1250°C
- Free forging or die forging to form rough shape
- Ring rolling for large diameters ensures uniform grain and density
c. Heat Treatment
- Normalizing: refine grains
- Quenching & Tempering: increase strength and toughness
- Solution Treatment: improve corrosion resistance for stainless steels
d. Machining
- Turning, drilling, chamfering, and polishing of sealing surfaces
- Surface roughness control:
- RF face: Ra 3.2–6.3 μm
- RTJ face: Ra ≤ 1.6 μm
e. Inspection and Testing
| Test Item | Method | Zweck |
| Visual & Dimensional | Calipers, visual check | Detect surface and size defects |
| NDT | UT / MT / PT | Check cracks and inclusions |
| Pressure Test | Hydro / Pneumatic | Verify sealing and strength |
| PMI Test | Spectrometer | Confirm material composition |
f. Surface Protection
- Carbon Steel: sandblasting + anti-rust primer or galvanization
- Stainless Steel: pickling & passivation + film protection
- Special coatings: epoxy or PTFE lining for anti-corrosion
g. Packing & Marking
- Small flanges: plastic + wooden cases
- Large flanges (≥1000mm): anti-shock wooden frame + moisture-proof film
- Markings: material, standard, heat number, and order reference.
Installation of Large Diameter Flanges
a. Pre-installation Check
- Verify dimensions, pressure rating, sealing face, and bolt hole alignment
- Ensure flange surfaces are clean, scratch-free, and corrosion-free
b. Alignment
- Coaxial tolerance ≤ 1.5‰ of OD or 2mm (whichever is smaller)
- Face parallelism deviation ≤ 0.3‰
- Use lifting tools or supports for positioning during installation
c. Gasket Installation
| Typ | Anwendung | Hinweise |
| Non-metallic (Graphite/PTFE) | Medium/low pressure | Ensure clean, centered placement |
| Spiral Wound | High pressure/high temperature | Must be concentric with bolts |
| Metal Ring (RTJ) | Ultra-high pressure | Fit precisely, not reusable |
d. Bolt Tightening
Tighten in cross-star sequence in 3–4 stages:
- 30–40% torque
- 60–70% torque
- Final 100% torque
- Recheck after 2 hours to ensure uniform stress.
e. Testing
- Hydrostatic Test: 1.5× design pressure
- Pneumatic Test: 1.1× design pressure
- Inspect for leakage before system start-up.
Common Installation Mistakes and Prevention
| Issue | Consequence | Verhütung |
| Fehlausrichtung | Uneven gasket stress → leakage | Use gauges, ensure precise alignment |
| Over-tightening | Gasket crush or flange distortion | Follow torque specs |
| Reusing gasket | Seal failure | Always use new gaskets |
| Dry bolts | Torque inaccuracy | Apply lubricant (graphite or MoS₂) |
| Incorrect sequence | Warping | Tighten symmetrically in cross pattern |
Häufig gestellte Fragen
Large flanges have bigger diameters, thicker sections, and stronger load capacity, suitable for higher pressure and temperature systems.
ASME B16.47 Series A/B, EN 1092-1, GB/T 9119, and HG/T 20592.
Metal spiral wound gaskets, RTJ ring joints, and graphite gaskets are most common.
Use corrosion-resistant materials like 316L, 2205, or C276; apply epoxy coating or hot-dip galvanization.
Requires large forging presses, CNC lathes, and UT inspection for internal integrity.
Abschluss
A large diameter flange is not just a mechanical connector — it’s a safety-critical component ensuring system integrity in some of the world’s most demanding industries.
From material selection and forging to precise machining, inspection, and controlled installation, every step determines the reliability, performance, and lifespan of the system.
When designed and installed according to ASME, EN, or GB standards, large flanges can safely operate under extreme pressures and temperatures, making them indispensable in global industrial infrastructure.
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