Socket-Weld Flanges are the standard for small-bore (NPS ≤ 3) chemical and instrumentation lines. Get a 4-hour quote.
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Pre-weld preheating and post-weld heat treatment records included per ASME B31.1 §127.3.
Socket-Weld Flanges (SW) are stepped-bore pipe connectors into which the pipe is inserted and fillet-welded at the socket shoulder, providing a smooth bore and reduced turbulence for small-bore high-pressure lines. As an ASME B16.5 socket-weld flange manufacturer, we produce SW flanges to ASME B16.5 (1/2"–3" NPS only, Class 150–600), EN 1092-1 Type 12, and JIS B2220 SW.
Socket-Weld flanges are restricted to small-bore service (NPS ≤ 3) per ASME B31.1 §127.3 because preheating and post-weld heat treatment (PWHT) become impractical on larger diameters. Socket-welded joints have a known crevice corrosion risk in creviced geometry: the gap between the pipe OD and the socket ID (typically 1.6 mm / 1/16" before welding) can accumulate process fluid and become a corrosion site.
After welding, the joint may require stress relief (PWHT) per ASME B31.3 §328.2 for certain service conditions. ASME B31.1 §127.3 requires PWHT for socket-weld joints in steam service above 1.5 MPa (220 psi) or temperature above 200°C.
Socket-Weld flanges are used in chemical injection systems (where the small-bore smooth bore is required to avoid deadlegs), instrument air lines, sample lines, hydraulic lines, and other small-bore high-pressure applications where Weld Neck flanges are impractical due to the pipe being too small for butt-welding.
Materials: A105 carbon steel (default), A350 LF2 low-temperature carbon steel (limited availability), A182 F304/F316 stainless steel. All supplied with EN 10204 3.1 mill certificate. ISO 9001:2015 quality management. PED 2014/68/EU CE-marking available on request.
Pressure-temperature rating: Class 150 SW flanges rated for 285 psi at 38°C, dropping to 150 psi at 400°C. Class 300 rated for 740 psi at 38°C, dropping to 415 psi at 400°C. Class 600 rated for 1480 psi at 38°C, dropping to 875 psi at 400°C. ASME B16.5 §6.1 restricts socket-weld to NPS ≤ 3 due to socket machining tolerances.
Manufacturing process: SW flanges are machined from forged billet. The socket depth and diameter must match ASME B16.5 §6.1 socket dimensions (depth = 0.5 × NPS for NPS ≤ 3, bore = pipe OD + 1/16" for the clearance). The weld end is machined to ASME B16.25 §3.4 socket-weld preparation. Pre-weld cleaning of the socket ID and pipe OD is required to remove machining oils and avoid weld porosity. PWHT is performed at 595-650°C for carbon steel and 1020-1075°C for stainless when specified.
Common applications: chemical injection (corrosion inhibitor injection into main pipelines, where the small-bore smooth bore avoids deadlegs), instrument air and gas lines, sample conditioning systems, hydraulic lines, small-bore high-pressure manifolds, and laboratory gas distribution. Socket-weld flanges are the standard specification for chemical injection quills (ASTM A106 + SW flange + nipple + check valve) in oil and gas upstream service.
Crevice corrosion mitigation: For austenitic stainless F304/F316 SW flanges in chloride-containing service, we recommend specifying F316L with controlled sulfur content (≤0.005%) and oxygen-inerting during welding. Alternatively, butt-weld Weld Neck flanges can be used to eliminate the crevice geometry entirely.
Shipping: Standard NPS 1/2"–2" Class 150 SW flanges in A105 carbon steel ship in 15–20 days from order confirmation. Non-stocked sizes, Class 300 and above, and stainless materials ship in 25–45 days. Sea freight from Shanghai/Qingdao to major ports in 14–30 days. Third-party inspection by SGS / BV / TUV / Intertek available on request.
Per ASME B31.1 §127.3, socket-weld joints in steam service above 1.5 MPa (220 psi) or temperature above 200°C (392°F) require PWHT. Per ASME B31.3 §328.2, PWHT is required for certain materials and service conditions. We recommend PWHT for any service where the operating temperature exceeds 200°C or where cyclic loading is expected. PWHT is performed at 595-650°C for carbon steel (A105) and at 1020-1075°C for austenitic stainless (F304/F316).
ASME B16.5 §6.1 defines Socket-Weld flanges only for NPS 1/2" through NPS 3". Above NPS 3, the socket diameter becomes too large to machine accurately and the gap between the pipe OD and the socket ID becomes excessive (weld shrinkage causes distortion). For NPS 4" and above, use Slip-On (SO) or Weld Neck (WN) flanges. EN 1092-1 Type 12 has the same NPS ≤ 3 restriction.
Not recommended. Socket-weld joints have a known crevice corrosion risk: the 1.6 mm (1/16") gap between the pipe OD and the socket ID before welding can accumulate process fluid and become a localized corrosion site. In sour H2S service per NACE MR0175 / ISO 15156, the crevice geometry is particularly susceptible to pitting and SCC. We recommend Weld Neck (WN) flanges for sour service.
Generally no. Socket-weld joints are permanent, the pipe is fillet-welded inside the socket, requiring either grinding the weld out (risking pipe wall damage) or cutting the pipe back to the next joint. For systems requiring frequent component replacement, use Threaded (Th) flanges or Weld Neck (WN) flanges with bolted connections. Socket-weld flanges are designed for permanent installations.
Socket-Weld (SW) flanges have a female socket bore, the pipe end is inserted and fillet-welded at the socket shoulder. Slip-On (SO) flanges have a cylindrical bore, the pipe slides through and is fillet-welded at both the pipe OD (outside the flange) and the flange face (inside the flange). SW flanges have a smooth bore transition (no internal weld bead protruding into the flow), making them preferred for chemical injection. SO flanges are cheaper and available in larger sizes (NPS ≤ 24 vs NPS ≤ 3 for SW).
Socket-Weld Flanges (SW) are stepped-bore pipe connectors into which the pipe is inserted and welded at the socket shoulder, providing a smooth bore and reduced turbulence for small-bore high-pressure lines. They conform to ASME B16.5 (1/2" to 3" NPS only), pressure ratings Class 150 (285 PSI) through Class 600 (1,480 PSI), with materials A105 and A350 LF2. Socket-weld flanges are restricted to small-bore service (NPS <= 3) per ASME B31.1 sec 127.3 because preheating and post-weld heat treatment become impractical on larger diameters. They are the standard specification for small-bore chemical and instrumentation lines.
Source: ASME B16.5-2020; EN 1092-1:2018.
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