Slip-On Flanges are the standard low-pressure utility choice. Get a 4-hour quote including bolt-pattern match check against your pipe schedule.
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Slip-On Flanges (SO) are short-hub pipe connectors that slip over the pipe outside diameter (OD) and are fillet-welded at both the top and inside of the flange face. As an ASME B16.5 slip on flange manufacturer and supplier based in Hebei, China, we produce SO flanges to ASME B16.5 (1/2"–24", Class 150–600), EN 1092-1 Type 02 (PN 10–PN 40), JIS B2220 SO, and HG/T 20592.
Slip-On flanges are easier to align during field installation than Weld Neck flanges because the pipe can be positioned through the bore before welding. This makes SO flanges popular for on-site fabrication and developing markets where skilled welding crews are scarce.
The defining limitation of the SO design is the reduced weld throat area compared to Weld Neck flanges. ASME B16.5 Class 150 and Class 300 SO flanges are dimensionally defined, but their use at Class 600 and above is generally not recommended for cyclic or high-temperature service. ASME B31.3 §A328.2 restricts SO flanges to non-cyclic service. SO flanges have only ~65% of the calculated fatigue life under cyclic pressure service compared to a WN flange of the same size and class.
Slip-On flanges are NOT recommended for service temperatures above 425°C, service temperatures below -29°C, or NACE MR0175 sour service. For these conditions, use Weld Neck (WN) flanges.
Typical applications: low-pressure water service (Class 150), fire water mains, compressed air, general utility piping, building services, HVAC. Slip-on flanges offer ~30% lower cost than weld-neck flanges for Class 150-300 service.
Materials: A105 carbon steel (default), A350 LF2 low-temperature carbon steel, A182 F304/F316/F316L stainless steel. All supplied with EN 10204 3.1 mill certificate. ISO 9001:2015 quality management. PED CE-marking available on request. For Class 600 and above service, Weld Neck (WN) flanges are preferred due to superior stress distribution and fatigue life.
Pressure-temperature rating follows ASME B16.5 Table 2-1.1 (Group 1.1 carbon steel). Class 150 SO flanges are rated for 285 psi at 38°C, dropping to 150 psi at 400°C. Class 300 SO flanges are rated for 740 psi at 38°C, dropping to 415 psi at 400°C. Class 600 SO flanges are rated for 1480 psi at 38°C, dropping to 875 psi at 400°C. For temperatures above 400°C or pressure above Class 600, Weld Neck flanges are recommended.
Manufacturing process: SO flanges are typically produced from forged billet (preferred for Class 300 and above) or rolled plate (Class 150). Hub height and bore diameter are machined per ASME B16.5 §6.1 tolerances. The pipe OD tolerance per ASME B36.10 (carbon steel) and B36.19 (stainless) must be matched: typical slip-on bore = pipe OD + 1/8" (3.2 mm) for Class 150, + 1/16" (1.6 mm) for Class 300. Weld preparation includes a 1.6 mm root face per ASME B16.25 for the fillet welds.
Materials: A105 carbon steel (default), A350 LF2 low-temperature carbon steel (-46°C to +345°C, normalized), A182 F304/F316/F316L stainless steel, 16MnDR Chinese low-temp, and duplex F51/F55 for sour service. All supplied with EN 10204 3.1 mill certificate. ISO 9001:2015 quality management. PED 2014/68/EU CE-marking under Module H available for EU shipments. NACE MR0175 hardness compliance (HRC ≤22) on request for sour service. ASME U-stamp / U2-stamp available on request for pressure vessel nozzle applications.
Common applications: water treatment piping, fire-protection mains, building services (HVAC chilled water), low-pressure chemical transfer lines, utility air lines, irrigation systems, and oilfield gathering lines in low-pressure service. SO flanges are preferred where fabrication speed matters more than fatigue life.
Shipping: Standard stocked sizes (1/2"–12" Class 150 in A105) ship in 15–20 days from order confirmation. Non-stocked sizes, large-bore (14"–24"), and custom alloys ship in 25–45 days. Sea freight from Shanghai/Qingdao to major ports in 14–30 days. Air freight available for urgent orders at 5–7× ocean cost. Third-party inspection by SGS / BV / TUV / Intertek available on request.
ASME B16.5 Class 600 Slip-On flanges are dimensionally defined in the standard, but their use at Class 600 pressure is generally not recommended for cyclic or high-temperature service. The reduced weld throat area (single fillet weld vs. full-penetration butt weld of WN) limits fatigue life to ~65% of an equivalent WN flange. ASME B31.3 §A328.2 restricts SO flanges to non-cyclic service. For Class 600 and above, or for cyclic / high-temperature service, use Weld Neck (WN) flanges instead.
At Class 150 (low pressure, ~285 psi at 100°F), the difference between SO and WN flanges is minimal for non-cyclic service. SO flanges are ~30% cheaper and easier to align in the field. WN flanges offer ~50% better fatigue life under cyclic pressure. For utility, water, and fire-protection service, SO is the standard choice. For any service involving pressure cycling, vibration, or temperature > 425°C, use WN.
The Slip-On flange bore must be larger than the pipe OD to allow the pipe to slide through during installation. Typical ASME B16.5 tolerance: Class 150 bore = pipe OD + 1/8" (3.2 mm), Class 300 bore = pipe OD + 1/16" (1.6 mm). The pipe OD tolerance per ASME B36.10 (carbon steel) and B36.19 (stainless) must be considered. If the gap is too small, the pipe will not slide. If too large, alignment becomes difficult. We recommend field-measuring the pipe OD before ordering.
Not recommended. ASME B31.3 §A328.2 restricts SO flanges to non-cyclic service, and NACE MR0175 sour service typically involves cyclic pressure and vibration. We recommend Weld Neck (WN) flanges for NACE MR0175 sour service. If SO flanges must be used (e.g. retrofitting an existing SO flange system to sour service), the fillet weld throat area must be 100% volumetrically inspected per ASME V Article 9 (radiographic) or Article 10 (ultrasonic), and hardness tested per NACE MR0175 §6.2.
Standard stocked sizes (1/2"–12" Class 150 in A105 carbon steel) ship in 15–20 days from order confirmation. Non-stocked sizes (14"–24"), Class 300 and above, or custom alloys (A350 LF2, A182 F304/F316, 16MnDR, duplex) ship in 25–45 days. Sea freight from Shanghai / Qingdao / Ningbo to Middle East (Jebel Ali, Dammam, Hamad) is 14–21 days, to South Asia (Mundra, Karachi) is 10–18 days, to Europe (Rotterdam, Hamburg, Genoa) is 28–35 days.
Slip-On Flanges (SO) are short-hub pipe connectors that slip over the pipe OD and are fillet-welded at both the top and inside of the flange face. They conform to ASME B16.5 (1/2" to 24" NPS), pressure ratings Class 150 (285 PSI) to Class 600 (1,480 PSI), materials A105 carbon steel, A350 LF2 low-temperature carbon steel, and 304/316 stainless. They offer ~30% lower cost than weld-neck flanges but have only ~65% of the calculated fatigue life under cyclic pressure service - therefore ASME B31.3 restricts SO flanges to non-cyclic low-pressure service. They are the standard specification for utility, low-pressure process, and fire-protection piping.
Source: ASME B16.5-2020; EN 1092-1:2018.
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