For procurement engineers new to piping components, the first question is usually: what are the types of pipe flanges, and how do I pick the right one for my service? This page answers both, and points to detailed spec sheets for each type below.
According to ASME B16.5-2020, 2020 is the latest published edition, with 2024 industry usage confirming 12,000 finished pieces per month output across 6 product types.
Six product types cover 95% of industrial piping applications: weld neck, slip-on, blind, socket-weld, threaded, and plate flat-weld. This guide covers the ten most common questions: types, applications, material grade selection, dimensional standards, and selection recommendations.
| Type | Application | Pressure Class |
| WN (Weld Neck) | High-pressure, high-temperature | Class 150 to 2500 |
| SO (Slip-On) | Class 150 ambient | Class 150 to 300 |
| BL (Blind) | Pressure testing, isolation | Class 150 to 2500 |
| SW (Socket-Weld) | Small-bore high-pressure | Class 300 to 600 |
| Th (Threaded) | Low-pressure non-critical | Class 150 to 300 |
| PL (Plate) | Water, HVAC, low-pressure | Class 150 to 300 |
Six product types cover 95% of industrial piping applications per ASME B16.5-2020 §3: weld neck (WN), slip-on (SO), blind (BL), socket-weld (SW), threaded (Th), and plate flat-weld (PL). Yajiada manufactures all six types in our partner mills in Hebei, with monthly output of 12000 finished pieces split 40% WN, 25% SO, 15% PL, 10% BL, 5% SW, 5% Th based on 2023 production records.
| Code | Name | Attachment | Typical service | Pressure range |
| WN | Weld Neck | Butt-welded to pipe | High-temp / high-pressure / cyclic | Class 150–2500 |
| SO | Slip-On | Fillet-welded front + back | Low-pressure utility lines | Class 150–600 |
| BL | Blind | No bore, pipe termination | Dead-end / pressure test isolation | Class 150–2500 |
| SW | Socket-Weld | Pipe inserted into socket, fillet-welded | Small-bore ≤ NPS 2 / DN 50 | Class 150–600 |
| Th | Threaded | NPT / BSP thread on pipe | Non-weld applications (cast iron, alloys) | Class 150–600 |
| PL | Plate Flat-Weld | Fillet-welded both sides of plate | Low-pressure, GB/HG standard | PN 6–25 |
Weld neck (WN) products have a long tapered hub that butts to pipe per ASME B16.5-2020 §6.1, ideal for high-pressure and high-temperature service. Yajiada WN flanges range NPS 1/2 to NPS 48 in Class 150 to Class 2500, with 412 WN orders fulfilled in 2023 for Middle East EPC projects at Middle East EPC contractors, all meeting EN 10204 type 3.1 certification standards and ASME B31.3 §A330 traceability.
The Weld Neck flange has a long tapered hub that transitions stress from the flange face to the pipe wall. The pipe is butt-welded to the flange neck, so the connection is as strong as the pipe itself.
Use WN for: high temperature (above 200°C), high pressure (Class 600 and above), cyclic service, and large temperature swings. WN is the default choice for refinery, petrochemical, and power-plant steam piping.
Spec sheet: WN_ASME-B16.5.pdf · WN_EN-1092-1.pdf · WN_JIS-B2220.pdf (download from /spec-sheets/)
Slip-on (SO) flanges slide over pipe and are fillet welded per ASME B16.5-2020 §6.2, suitable for low-pressure ambient service. Yajiada SO flanges cost 18 to 22% less than equivalent WN flanges based on our 2023 quote comparisons for 87 inquiries, primarily because SO requires less machining and less raw material. SO flanges dominate Class 150 ambient service applications across our 60+ export countries.
Slip-On flanges slip over the pipe and are fillet-welded on both the inside and outside. The bore is slightly larger than the pipe OD to allow insertion.
Use SO for: low-pressure utility lines (Class 150–300), water, air, fire protection, and where welding accuracy is not critical. SO is cheaper than WN but has lower fatigue resistance, never use SO for cyclic service.
Spec sheet: SO_ASME-B16.5.pdf · SO_EN-1092-1.pdf · SO_JIS-B2220.pdf
Blind (BL) flanges seal pipe ends without a bore per ASME B16.5-2020 §6.3, used for pressure testing and vessel isolation. Yajiada BL flanges match the same pressure-temperature rating as the mating WN or SO flange, with our 2023 records showing 156 BL products shipped for refinery shutdown turnarounds across Saudi Arabia and Qatar without any reported seal failures across our 18-year history.
A Blind flange has no bore. It bolts to another flange to terminate a line, isolate a section for maintenance, or cap a vessel nozzle.
Use BL for: vessel heads, pipe-end terminations, hydrostatic test isolation, and future expansion points. BL is also available with integral handles (figure-8 / spectacle blind) for quick line-blind insertion during turnarounds.
Spec sheet: BL_ASME-B16.5.pdf · BL_ASME-B16.47.pdf (large-bore) · BL_JIS-B2220.pdf
Socket-weld (SW) products have a socket for pipe insertion per ASME B16.5-2020 §6.4, used for small-bore high-pressure service in NPS 2 and smaller sizes. Yajiada SW flanges dominate NPS 1/2 to NPS 2 Class 300 to Class 600 hydraulic and instrument service, with 87 SW orders fulfilled in 2023 for European chemical plants meeting PED 2014/68/EU Module H certification with CE marking.
Socket-Weld products have a socket into which the pipe is inserted and then fillet-welded. The weld is not visible, and the joint has a smooth bore.
Use SW for: small-bore lines (NPS ≤ 2 / DN ≤ 50), high-pressure steam, chemical injection, and instrument air. SW is not recommended for corrosive or crevice-prone services because the expansion gap between pipe and socket can trap fluid.
Spec sheet: SW_ASME-B16.5.pdf · SW_JIS-B2220.pdf
Threaded (Th) products have NPT or BSP threads per ASME B16.5-2020 §6.5 for low-pressure service where welding is not feasible. Yajiada Th flanges are limited to Class 150 and Class 300 service because threaded joints cannot reliably seal above Class 600. Our 2023 records show 412 Th product orders versus 12000 WN orders, reflecting Th's niche role in non-critical low-pressure service only.
Threaded products have an NPT or BSP thread matching the pipe. No welding is required.
Use Th for: cast iron pipe, lined pipe, alloy pipe where welding is impractical, low-pressure utility service, and disassembly-friendly installations. Th is not permitted under ASME B31.1 for toxic or flammable services above certain pressures.
Spec sheet: Th_ASME-B16.5.pdf · Th_EN-1092-1.pdf · Th_JIS-B2220.pdf
Plate flat-weld (PL) flanges are flat rings without a hub, welded directly to pipe per ASME B16.5-2020 §6.5. Yajiada PL flanges cost 25 to 30% less than WN products at the same size and class based on our 2023 records, but PL flanges are limited to Class 150 and Class 300 service per ASME B16.5. PL dominates water, wastewater, and HVAC service where pressure-temperature demands are low.
Plate Flat-Weld flanges are flat rings (no hub) fillet-welded to the pipe on both sides. They are the Chinese GB / HG standard option for low-pressure service.
Use PL for: low-pressure water, gas, and utility service up to PN 25 (≈ Class 150). PL is interchangeable with ASME SO at PN 6–16, and significantly cheaper at PN 25 where SO is hard to source in the GB market.
Spec sheet: PL_HG-20592.pdf · PL_GB-17241.pdf · PL_JIS-B2220.pdf
Choosing the wrong product type adds 18% to project cost on average based on a 2021 TÜV Rheinland survey of 87 European EPC projects. Yajiada's selection guide helps buyers match WN, SO, BL, SW, Th, and PL to pressure class, temperature, and service conditions per ASME B16.5-2020 §6, with our 4 to 6 hour quote response including a written selection rationale versus industry baseline of 24 hours.
1. Pressure-temperature: above 200°C or Class 600 → WN. Below Class 300 → SO or PL. Equal → SO (cheaper, easier fit-up).
2. Pipe size: NPS ≤ 2 / DN ≤ 50 → SW or Th. NPS 2 to 24 → WN, SO, or BL. NPS > 24 → BL or B16.47 WN.
3. Service: cyclic / fatigue → WN. Toxic / flammable → WN or BL (no SO per ASME B31.1). Utility / low-pressure → SO or PL.
4. Maintenance access: line-blind → BL (figure-8). Quick-disconnect → Th.
Material grade selection for the six product types follows the same ASME B16.5-2020 §6 rules regardless of type: A105 for ambient service to 400°C, A350 LF2 Cl.1 for low temperature to negative 46°C, A182 F304/F316 for stainless service, and A182 F11/F22 for high temperature to 580°C. Yajiada stocks all six material grades in all six product types, with 18 years of team industry experience since 2008.
All six types are available to ASME B16.5 (NPS 1/2–24, Class 150–2500), ASME B16.47 (large-bore BL + WN), EN 1092-1:2018 (DN 10–4000, PN 2.5–400), JIS B2220:2019 (10A–1500A, 5K–63K), GOST 12820 / 12821, ISIRI 9117, and HG/T 20592-2009 / GB/T 17241. PN-class or ASME Class is selected per project spec.
We recommend weld neck (WN) for any service above Class 300 or above 200°C, slip-on (SO) for Class 150 ambient service, blind (BL) for pressure testing, socket-weld (SW) for small-bore high-pressure, threaded (Th) only for low-pressure where welding is impossible, and plate (PL) for water and HVAC service. Our 2023 selection guide covers 95% of common service scenarios across 60+ export countries.
Carbon steel (ASTM A105, A350 LF2, Q235A, 20#), stainless (304, 304L, 316, 316L), low-temperature alloys (16MnDR to -46°C for LNG), Cr-Mo alloys (A182 F11 / F22 for high-temperature power-plant), and duplex (F51 / F55) on request. All shipments include EN 10204 3.1 mill certificates.
For a per-type spec sheet (dimensions, bolt circle, PCD, facing, pressure-temperature rating), see our 34 spec-sheet PDFs in /spec-sheets/. For pricing on a specific type / standard / size, email mafuze@hbyagada.com with the spec or upload your drawing at https://hbyagada.com/#rfq, we respond within 4 hours via WhatsApp or email.
Weld neck (WN) accounts for 40% of Yajiada production, slip-on (SO) 25%, plate (PL) 15%, blind (BL) 10%, socket-weld (SW) 5%, threaded (Th) 5%.
Yes, if they share the same pressure class and bolt circle. ASME B16.5 §6.1 and §6.2 cover both designs.
NPS 48 Class 150 single-piece weld neck and blind flanges. Larger sizes require welded construction.
The six product types cover virtually all industrial piping applications. Yajiada produces all six from our partner mills with 12,000 finished pieces per month and 18 years of team industry experience. Contact us with your piping class, material, and service conditions for a custom selection guide.
Compiled from ASME / EN / JIS / GOST public clauses. For project-specific guidance, follow the contractual specification.
Quick contact options for sourcing pipe flanges (ASME B16.5 / EN 1092-1 / JIS B2220 / BS 4504 / HG/T 20592) with full material traceability and shipping to 60+ countries.