Certified forged steel piping components built to ASME B16.5, EN 1092-1, and DIN specs for heavy industrial pipelines.
Demystifying Nominal Diameter (DN), Nominal Pressure (PN), and cross-standard interchangeability in industrial plant design.
In modern process engineering, DN Flange Dimensions (Diamètre Nominal / Nominal Diameter) serve as the global metric standard for specifying pipe size, bolt hole patterns, facing diameters, and pressure ratings across international borders. Defined primarily under European (EN 1092-1, DIN) and International (ISO 7005-1) standards, the DN designation system provides a standardized baseline that allows engineering procurement contractors (EPCs) to achieve seamless structural integrity in cross-border oil, gas, chemical, and marine piping systems.
While DN indicates the approximate inside diameter of a pipe in millimeters (e.g., DN 50 = 50 mm), it does not represent an exact physical measurement of internal bore. Instead, it correlates directly to Nominal Pipe Size (NPS) in inches. For instance, DN 15 = ½", DN 25 = 1", DN 50 = 2", DN 100 = 4", DN 300 = 12", and DN 600 = 24". Matching these dimensions with correct PN (Pression Nominale) pressure classes is critical to preventing mechanical failure under thermal expansion.
When calculating load tolerances, gasket seating stress, and bolt torques for DN flange assemblies, piping engineers must evaluate five fundamental dimensional variables:
The total external diameter of the forged flange plate. Determines structural clearance in compact module skids and pipe racks.
The precise center-to-center diameter connecting all bolt holes. Essential for flange alignment during field installation.
The internal fluid path diameter. Must match internal pipe schedule (e.g., STD, XS, Sch 80) to eliminate flow turbulence and erosion.
Calculated structural thickness required to resist bending moments and shear stresses caused by internal fluid pressure.
Comparative reference table showing key dimensions for EN 1092-1 PN 16 Weld Neck (Type 11) and Slip-On (Type 01) flanges.
| Nominal Size (DN) | NPS Equivalent | Flange Outer Dia (D) [mm] | Pitch Circle (K) [mm] | No. of Bolt Holes (L) | Bolt Hole Dia (d2) [mm] | Flange Thickness (C) [mm] | Matched PN Rating |
|---|---|---|---|---|---|---|---|
| DN 15 | 1/2" | 95 | 65 | 4 | 14 | 16 | PN 10 / PN 16 / PN 40 |
| DN 25 | 1" | 115 | 85 | 4 | 14 | 18 | PN 10 / PN 16 / PN 40 |
| DN 50 | 2" | 165 | 125 | 4 | 18 | 20 | PN 16 |
| DN 80 | 3" | 200 | 160 | 8 | 18 | 20 | PN 16 |
| DN 100 | 4" | 220 | 180 | 8 | 18 | 22 | PN 16 |
| DN 150 | 6" | 285 | 240 | 8 | 22 | 24 | PN 16 |
| DN 200 | 8" | 340 | 295 | 12 | 22 | 26 | PN 16 |
| DN 300 | 12" | 460 | 410 | 12 | 26 | 32 | PN 16 |
| DN 500 | 20" | 715 | 650 | 20 | 33 | 46 | PN 16 |
* Note: Custom larger sizes up to DN 3000 (120 inches) and higher pressure ratings up to PN 400 (Class 2500) are manufactured per drawing specifications.
Why leading global EPCs source heavy industrial forged flanges from China's premier forging capital.
Shanxi Yuxin Casting & Forging Co., Ltd. operates within Dingxiang County, recognized globally as the “Hometown of Forging in China.” This industrial ecosystem provides immediate access to high-grade steel billets, specialized heat-treatment facilities, and advanced machining workshops, dramatically reducing raw material procurement costs and production cycle times.
Unlike trading entities, Shanxi Yuxin maintains end-to-end control over the entire production chain: raw steel cutting, closed-die and ring-rolling forging, normalizing/tempering heat treatment, high-precision CNC machining, drilling, and hydrostatic testing. Every step is linked directly to heat numbers for 100% material traceability.
With an annual forging output exceeding 10,000 metric tons of finished flanges and 2,000 tons of specialized forged parts, our plant delivers unmatched scale economies. This allows global buyers to benefit from competitive bulk pricing while securing guaranteed production slots during tight project deadlines.
Strict adherence to European Pressure Equipment Directives, ASME codes, and zero-defect QA testing protocols.
Fully certified under the European Pressure Equipment Directive (PED) and AD 2000-Merkblatt W0. Certified for supply into safety-critical pressure vessel systems across EU member states.
Every batch is shipped with a comprehensive Mill Test Certificate (MTC) detailing chemical ladle analysis, mechanical yield/tensile testing, impact values at -40°C, and heat treatment charts.
Engineered for H2S-containing sour gas fields. Carbon and alloy steel forgings undergo hardness testing and HIC/SSCC microstructural evaluation to eliminate hydrogen cracking risks.
100% Ultrasonic Testing (UT) for internal void detection, Magnetic Particle Inspection (MT), Dye Penetrant Testing (PT), and Positive Material Identification (PMI) spectral analysis prior to packing.
Tailored flange designs engineered to withstand extreme temperatures, cyclic fatigue, and corrosive environments.
High-pressure Weld Neck (Type 11) and Ring Type Joint (RTJ) Flanges in Class 900 to Class 2500 (DN 15 to DN 600). Forged from ASTM A182 F51 Duplex or A350 LF2 low-temperature carbon steel, preventing flange leakage under deep-sea pressures and dynamic wave action.
Custom Tube Sheets, Slip-On Flanges, and Stub End Lap Joint Flanges fabricated in ASTM A182 F316L and F304 stainless steels. Designed to handle concentrated acids, organic solvents, and high-temperature cracking reactions without intergranular corrosion.
Large-diameter ASME B16.47 Series A/B Weld Neck Flanges up to DN 3000 (120") in high-alloy A182 F11 and F22 chrome-moly steel. Engineered for high-pressure steam distribution headers subject to thermal creep and high-cycle fatigue.
How digital manufacturing, green steel initiatives, and automation are reshaping global piping component procurement.
As global energy transitions toward clean hydrogen, flange manufacturing demands zero-porosity forging methods. Standard carbon steel is replaced by micro-alloyed steels resistant to hydrogen embrittlement at elevated pressures up to 700 bar.
Integrating 5-axis CNC machining centers with real-time laser tool-wear sensors ensures bolt hole pitch tolerances within ±0.1 mm and flange face surface finishes within exact 3.2–6.3 μm Ra limits, eliminating bolt alignment delays on site.
Future EPC projects require QR-code laser marking directly on the flange rim. Scanning the code instantly reveals the digital twin: chemical heat analysis, ultrasonic scanning video clips, dimensional 3D scans, and shipping history.
Expert technical responses to common buyer inquiries regarding standards, pressure classes, and custom manufacturing.
While EN 1092-1 uses Metric DN (e.g., DN 50) and ASME B16.5 uses Imperial NPS (e.g., 2"), they are conceptually equivalent in pipe size. However, their bolt hole pattern, pitch circle diameter (PCD), flange thickness, and gasket facing dimensions ARE NOT directly interchangeable. For example, a DN 50 PN 16 flange has 4 bolt holes on a 125mm PCD, whereas an ASME 2" Class 150 flange has 4 bolt holes on a 120.7mm (4.75") PCD. Adapter flanges or dual-standard drilled flanges must be specified when connecting EN and ASME piping modules.
EN 1092-1 categorizes forged flanges by design geometry:
• Type 01 (Plate / Plain Flange): Flat plate slipped over the pipe and fillet welded; ideal for low-pressure lines.
• Type 02 (Loose Plate Flange): Used with a weld-on collar or stub end; allows easy rotation for bolt alignment.
• Type 05 (Blind Flange): Solid disc used to block the end of a piping system or vessel nozzle.
• Type 11 (Weld Neck Flange): Features a tapered forged hub welded directly to the pipe; superior resistance to high pressure and thermal cycles.
• Type 12 (Hubbed Slip-On Flange): Features a raised hub for strength; slipped over pipe before double welding.
For standard ambient service, ASTM A105 / Q235B carbon steel is cost-effective. For low-temperature service down to -46°C (e.g., LNG terminals), ASTM A350 LF2 Class 1 with Charpy V-notch impact testing is specified. For high-temperature, high-pressure steam utility boilers, alloy steel ASTM A182 F11 or F22 is required. For corrosive offshore oil and chemical applications, ASTM A182 F304/F316L or Duplex F51/F53 provides optimal pitting resistance.
Yes. Utilizing our specialized ring-rolling equipment and large-scale vertical CNC boring mills, we produce custom non-standard flanges, heavy forged rings, expansion joint flanges, and heat exchanger tube sheets up to 3,000 mm (120 inches) in outer diameter according to customer drawings, CAD files, or finite element stress analysis requirements.
To prevent atmospheric corrosion during trans-ocean shipment, flanges receive yellow rust-preventive varnish, black anti-corrosion paint, transparent oil coating, or hot-dip galvanizing. Machined raised faces are protected with plastic caps. Flanges are loaded into ISPM 15 compliant fumigation-free plywood crates or solid steel-framed pallets with heavy-duty plastic wrapping.
Explore our full export range of CNC machined blind, reducer, weld neck, and plain flanges manufactured for global stockists.
