Slip-on Raised Face Flanges (SORF)

A slip-on raised face flange is a pipe connection component that slides over the outside diameter of a pipe end and is secured with two fillet welds — one at the back of the hub and one at the pipe bore inside the flange. The 'raised face' is a machined ring protruding above the flange face, which concentrates bolt load on the gasket for a reliable pressure seal. SORF flanges per ASME B16.5 are used across oil & gas, petrochemical, power, and water treatment piping where ease of installation and access for maintenance are priorities.

SORF flanges offer lower material cost compared to weld neck flanges, simpler installation requiring only fillet welds, easier alignment during fit-up, and suitability for frequent assembly/disassembly. They are ideal for Class 150-300 low-to-medium pressure service. The raised face design improves gasket seating and sealing efficiency over flat face designs. Their hub design also provides more resistance to bending moments than plain slip-on designs, while remaining significantly more economical than weld neck alternatives for non-critical service.

ASME B16.5 slip-on raised face flanges are manufactured in pressure classes 150, 300, 400, 600, 900, 1500, and 2500 LBS. Class 150 is the most common for general process piping at moderate pressures. For high-pressure applications (Class 600+), weld neck flanges are typically preferred for structural integrity — consult your piping engineer. DIN standard ND-6, 10, 16, 25, and 40 bar ratings are also available for European-specification projects.

A 6-inch Class 150 slip-on flange weighs approximately 19 lbs (8.6 kg) per the standard B16.5 weight chart. For the same size, Class 300 SO flanges weigh approximately 39 lbs (17.7 kg), and Class 600 approximately 80 lbs (36.3 kg). Weights increase significantly with pressure class due to the additional flange thickness and bolt circle diameter required. Actual weights may vary slightly by manufacturer based on machining tolerances — refer to Amardeep Steel's detailed weight chart above for precise values.

For ASTM A105 carbon steel Class 150 slip-on raised face flanges, the ASME B16.5 pressure-temperature rating starts at 285 psig at -20°F to 100°F, dropping to 260 psig at 200°F, 230 psig at 300°F, 170 psig at 500°F, and 20 psig at 1000°F. Stainless steel flanges (F304, F316) have different PT ratings per ASME B16.5 Table 2-2.2 and 2-2.3. Always verify the applicable group (1.1 through 3.3) for your specific material and operating conditions.

ASME B16.5 covers slip-on flanges in nominal pipe sizes NPS ½ through NPS 24. ASME B16.47 covers large-diameter flanges from NPS 26 through NPS 60 in two series: Series A (formerly MSS SP-44) used primarily in pipelines, and Series B (formerly API 605) used in industrial piping. For slip-on flanges above 24 inches, B16.47 Series A or B applies depending on the project specification. Amardeep Steel manufactures flanges to both standards through NPS 48.

Yes, with appropriate material selection. SORF flanges in alloy steel F11, F22, and F91 are suitable for high-temperature service in power plants and refinery heater piping up to 1050-1200°F depending on grade. However, the fillet weld joint used in slip-on flanges is inherently weaker under thermal cycling and high-stress conditions compared to the butt-weld joint of a weld neck flange. For cyclic, high-fatigue, or critical service above Class 600, most piping codes and engineering standards recommend weld neck flanges over slip-on designs.

The standard gasket for raised face flanges is the spiral wound gasket with inner and outer rings per ASME B16.20. For Class 150 and 300, a full sheet compressed non-asbestos fiber (CNAF) gasket or graphite gasket is also used in lower-criticality services. Spiral wound gaskets with AISI 316 winding and graphite filler are the most common in refinery service. The gasket OD must not exceed the inner edge of the bolt holes, and the ID should match the pipe bore. Always specify gasket dimensions to match the raised face dimensions of your specific flange class and size.

ASME B16.5 specifies a 125-250 AARH (Ra 3.2-6.3 µm) serrated phonographic or concentric finish as standard for raised face flanges. This controlled roughness anchors the gasket and prevents blowout. Some services require a smoother 32-63 AARH finish for PTFE envelope or soft metal gaskets. Rougher mill finishes above 250 AARH are not acceptable for pressure sealing. Specify the required surface finish on your purchase order if your project requires a deviation from the B16.5 standard finish.

Standard documentation includes EN 10204 Type 3.1 Material Test Certificates covering chemical composition, mechanical properties (tensile, yield, elongation, hardness), heat treatment records, and dimensional inspection report per ASME B16.5. Third-party 3.2 certificates are available on request with prior order confirmation. Export orders include a packing list, commercial invoice, certificate of origin, and third-party release note when TPI is engaged. NACE hardness records, PMI (Positive Material Identification) reports, and pressure test certificates are supplied when specified at order stage.