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ANSI B16.5 · High Pressure / High Temperature Service
Welding Neck Flanges
M.S. Welding Neck Flanges Manufacturer & Supplier – Mumbai, India · Since 1999
ANSI B16.5 CertifiedHigh Pressure ServiceButt Weld EndDirect ManufacturerPAN India Supply
M.S. Welding Neck Flanges (WN Flanges) are the most robust and widely used flange type for demanding high-pressure, high-temperature and cyclic service applications. The distinctive long tapered neck is butt-welded directly to the pipe — distributing mechanical stress uniformly and providing superior resistance to fatigue, bending and thermal cycling. Manufactured from IS:2062 grade mild steel at our Darukhana, Mumbai factory to ANSI B16.5 standard. Available in sizes 15mm NB to 600mm NB, Schedule 40 to XXS, Class 150 to Class 2500. Standard choice for oil & gas refineries, petrochemical plants and power stations.
Quick Specifications
StandardANSI B16.5 / IS
Size Range15mm NB – 600mm NB
Pressure ClassClass 150, 300, 600, 900, 1500, 2500
ScheduleSCH 40 to SCH 160 / XXS
Face TypesRaised Face (RF) / Ring Joint (RTJ)
Material GradeIS:2062 Mild Steel (MS)
Lead Time3–10 Days (Standard) | 10–20 Days (Large Sizes)
SupplyPAN India | Darukhana, Mumbai
25+Years Mfg.
Class 2500Max Rating
600mmMax NB Size
What Are Welding Neck Flanges?
Welding Neck Flanges (WN Flanges or Weld Neck Flanges) have a long conical hub (neck) that transitions from the flange body to the pipe wall thickness. This neck is butt-welded to the pipe end, creating a continuous metal flow path with gradual stress distribution — eliminating the stress concentration at the flange-pipe junction that exists in slip-on or socket weld flanges.
The bore of a welding neck flange is matched (bored) to the inside diameter of the mating pipe, ensuring a smooth internal bore with no step change that could cause turbulence. This makes WN flanges the preferred choice for high-velocity flow, erosive service and slurry pipelines in addition to high-pressure applications.
Why Welding Neck Flanges for High-Pressure Service?
- Stress distribution — Tapered hub transfers load gradually to the pipe wall
- Fatigue resistance — Best flange type for cyclic pressure and thermal cycling
- Smooth bore — No turbulence-causing step at the flange-pipe junction
- Radiographic inspection — Butt weld can be fully RT/UT inspected for quality assurance
- Full penetration butt weld — Highest integrity joint, no crevice for corrosion
Why Choose I.S. Engineering Co.?
25+ Years Experience
Manufacturing Welding Neck Flanges in Mumbai since 1999. Trusted by 500+ clients across India.
Factory-Direct Pricing
No middlemen. Buy direct from the manufacturer at the most competitive prices in Mumbai.
100% Quality Inspected
Every Welding Neck Flanges undergoes dimensional and material inspection before dispatch from our Mumbai factory.
PAN India Delivery
Supplying to Mumbai, Pune, Delhi, Bangalore, Chennai, Hyderabad, Ahmedabad and all major cities across India.
Welding Neck Flanges – Dimensional Specifications
| Class | Pressure (bar @ 38°C) | Temperature Range | Typical Application |
|---|---|---|---|
| Class 150 | 19.6 bar (285 PSI) | -29°C to +538°C | General process, utilities |
| Class 300 | 51.1 bar (740 PSI) | -29°C to +538°C | Higher pressure process |
| Class 600 | 102.1 bar (1480 PSI) | -29°C to +538°C | Oil & gas transmission |
| Class 900 | 153.2 bar (2220 PSI) | -29°C to +538°C | High-pressure gas systems |
| Class 1500 | 255.3 bar (3705 PSI) | -29°C to +538°C | Wellhead, HP process |
| Class 2500 | 425.5 bar (6170 PSI) | -29°C to +538°C | Ultra-high pressure critical |
* Dimensions are indicative. Custom sizes available on request. Contact I.S. Engineering Co. at +91 83558 15350 for specific sizes, tolerances and full specification sheets.
Welding Neck Flanges – Industries & Applications
Oil & Gas Refineries
Primary flange type for crude oil, refined products and gas pipelines. Class 300–600 WN flanges used in refinery process units. Class 900–2500 in wellhead and high-pressure gas service.
Petrochemical Plants
Used in cracking units, distillation columns, heat exchangers and reactor piping. High-temperature and high-pressure process streams require WN flanges for their superior stress distribution.
Power Plants
Used in steam pipelines, boiler connections and turbine inlet piping. Class 600–900 WN flanges for high-temperature high-pressure steam service in thermal power plants.
Chemical Processing
Critical process lines carrying corrosive chemicals, catalysts and high-temperature fluids. WN flanges ensure reliable, fatigue-resistant connections in demanding chemical environments.
Cryogenic Service
Used in LNG, LPG and cryogenic storage facility piping. Material and pressure class selected for sub-zero temperature service (typically -29°C to -196°C for cryogenic applications).
High-Velocity Flow
Used in slurry pipelines and high-velocity flow systems where smooth bore and erosion resistance are critical. Matching bore to pipe eliminates the turbulence-creating step of slip-on flanges.
Welding Neck Flanges – Frequently Asked Questions
What are Welding Neck Flanges?
+Welding Neck Flanges (WN Flanges) are pipe flanges with a long tapered hub that is butt-welded to the pipe end. The tapered neck distributes stress from the flange to the pipe gradually, making WN flanges the most fatigue-resistant flange type — the standard choice for high-pressure, high-temperature and cyclic service in oil & gas, power and petrochemical industries.
Why are Welding Neck Flanges preferred for high-pressure service?
+Welding Neck Flanges provide: (1) Gradual stress distribution through the tapered neck; (2) Best fatigue resistance for cyclic pressure and thermal cycling; (3) Smooth bore matched to pipe ID — no turbulence or erosion; (4) Full-penetration butt weld — highest integrity joint that can be RT/UT inspected; (5) Widest pressure range — Class 150 to Class 2500.
What is the difference between Welding Neck and Slip-On Flanges?
+Welding Neck Flanges are butt-welded to the pipe and are suitable for high-pressure, high-temperature and cyclic service. Slip-On Flanges slip over the pipe and are fillet-welded — easier to install and lower cost but suitable only for low-to-medium pressure, non-cyclic service. WN flanges cost more but provide superior performance in demanding applications.
What schedule (wall thickness) options are available?
+Welding Neck Flanges are available in schedules from SCH 20 to SCH 160 and XXS (extra-extra strong). The schedule of the flange bore must match the schedule of the connecting pipe. Standard schedules available: SCH 40 (standard), SCH 80 (extra strong), SCH 120, SCH 160 and XXS.
What sizes of Welding Neck Flanges are available?
+I.S. Engineering Co. manufactures Welding Neck Flanges in sizes from 15mm NB (½ inch) to 600mm NB (24 inch) in Class 150 to Class 2500. Specify NB size, pressure class and bore schedule when ordering. Custom bores to match non-standard pipe wall thicknesses are available on request.
What schedule bore is available for Welding Neck Flanges?
+Welding Neck Flanges are available in bore schedules from SCH 20 to SCH 160 and XXS (extra-extra strong). The schedule of the flange bore must match the schedule of the connecting pipe. Standard schedules available: SCH 40 (standard wall), SCH 80 (extra strong), SCH 120, SCH 160 and XXS.
Can Welding Neck Flanges be used in high-temperature steam service?
+Yes. Welding Neck Flanges are the preferred choice for high-temperature steam service in boilers, steam headers and turbine connections. The butt-welded joint and tapered neck provide superior resistance to thermal cycling and creep — critical in high-temperature steam systems at power plants and industrial steam users.
What is the lead time for Welding Neck Flanges?
+Standard Welding Neck Flanges in common sizes (15mm–300mm NB) are typically available within 3–10 working days. Larger sizes (350mm–600mm NB) and higher pressure classes (Class 900–2500) may require 10–20 working days. Call +91 83558 15350 for current stock and urgent delivery options.
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