Stainless Steel Pipe and Fittings

A stainless steel pipe system is an ideal choice for transporting corrosive or sanitary fluids, slurries, and gases, especially in applications involving high pressure, high temperature, or corrosive environments. Stainless steel’s aesthetic appeal also makes it suitable for architectural purposes.

Stainless steel pipes are typically defined as heavy-wall tubing with dimensions specified by the American National Standards Institute (ANSI). These dimensions include the outside diameter—denoted by NPS (imperial) or DN (metric)—and wall thickness, which is categorized by the schedule number. The ASME B36.19M standard governs these specifications.

Stainless steel pipes and fittings are provided in an annealed condition to facilitate fabrication and ensure optimal corrosion resistance. Additionally, Inox Fittings offers stainless steel pipes with an abrasive-polished exterior, suitable for architectural use.

Welded Pipes

Welded stainless steel pipes are made from 2B or HRAP stainless steel strips that are shaped, longitudinally welded, and annealed.

  • Larger pipes are fabricated from plates.
  • Welds are completed without filler metal, except for very large diameters.
  • Standard pipe lengths are either 6.0 or 6.1 meters.

Specifications:

  • ASTM A312M — Austenitic
  • ASTM A358M — Austenitic (large diameter)
  • ASTM A790M — Duplex

Seamless Pipes

Seamless stainless steel pipes are manufactured from hollow billets that are pierced and cold drawn to the required size, followed by annealing.

  • Standard seamless pipes are available in lengths of 6.1 meters up to DN 150 (NPS 6) and longer lengths as required.

Specifications:

  • ASTM A312M — Austenitic
  • ASTM A790M — Duplex

Joining and System Integration

Stainless steel piping systems can be joined using butt welding or threaded connections, particularly for heavier schedules like 40S and 80S.

The complete piping system includes complementary fittings and flanges, which are designed to match the same DN or NPS designators and schedule numbers as the pipes.

Butt Welding Pipe Fittings

Butt welding fittings offer several advantages, making them a superior choice for piping systems:

  • Leak-Proof: Welding ensures a permanent, leak-free connection.
  • Enhanced Strength: The continuous metal structure between the pipe and fitting strengthens the system.
  • Improved Flow: Smooth inner surfaces and gradual directional changes reduce pressure loss, turbulence, and minimize corrosion and erosion.
  • Space Efficiency: Welded systems require minimal space.

Inox Fittings provides butt welding fittings in these forms:

  • Elbows: Available in 45° and 90°; long radius is standard, but short radius options are also available.
  • Return Bends: 180° bends available in long radius (standard) and short radius.
  • Reducers: Concentric and eccentric types.
  • Tees: Equal and reducing.
  • Caps: End caps for pipe closure.
  • Stub Ends: Type B, compliant with MSS SP-43.

Butt welding fittings are available in seamless or welded construction and comply with ASTM A403M (or ASTM A815M for Duplex grades) and ASME B16.9 standards.

Screwed and Socket Weld Fittings

Screwed fittings are used to connect piping systems and are available in:

  • BSP-threaded (150lb) low-pressure fittings.
  • NPT/BSP-threaded (Class 3000) high-pressure fittings, made of Grade 316.

Socket weld fittings are suitable for high-pressure piping and are manufactured in Grade 316L to accommodate schedule 80S wall thickness piping.

Specifications:

  • ASTM A182M (Class 3000 NPT and socket weld).
  • ASME B16.11.
  • ISO 4144 (BSP dimensions).

Pipe Flanges

A flange is a steel ring (forged, cut from plate, or rolled) used to connect:

  • Sections of pipe.
  • A pipe to a pressure vessel, valve, pump, or other integral flanged assembly.

Flanges are joined by bolting to one another and are attached to the piping system by welding or threading. Stub ends are used for loose flanges.

Types of flanges include:

  • Slip-on
  • Blind
  • Weld neck
  • Threaded
  • Socket weld
  • Lap joint
  • Orifice

Forged stainless steel flanges are designed to accommodate the following pressure ratings:
Classes 150, 300, 600, 900, 1500, and 2500. The standard sealing face type is Raised Face (RF).

Manufacturing Specifications:

  • ASTM A182M and ASME B16.5.
    (Flanges exceeding NPS24/DN 600 conform to ASME B16.47, API 605, or BS 3293.)

Plate stainless steel flanges are forged or machined from plates specified in Table 'D,' Table 'E,' and others.

Manufacturing Specifications:

  • AS2129.

Waterworks flanges compliant with AS4087 and PN16 flanges to EN 1092-1 are also available upon request.

Types and Applications of Flanges

  • Slip-on Flanges: These slide over the pipe and are welded inside and outside for strength and leak prevention. They can also serve as backup flanges with Type B stub ends.

  • Blind Flanges: Used to seal off a piping system or vessel opening, blind flanges have no center bore.

  • Weld Neck Flanges: Preferred for high-stress applications, these flanges are designed to join piping systems via butt welding. They are more expensive due to their design.

  • Lap Joint Flanges: Similar to slip-on flanges, these have a radius at the center bore and flange face intersection to fit a Type A lap joint stub end. Lap joint flanges and Type A stub ends are not commonly stocked in Australia.