Stainless Steel Socket Weld Flange

Zhejiang Chengjiu Pipeline Co., Ltd. is one of the most reliable manufacturers and suppliers of stainless steel socket weld flange in China, also supports customized service. Please feel free to buy high quality stainless steel socket weld flange from our factory. Good service and reasonable price are available.

A Stainless Steel Socket Weld Flange has a counterbored socket machined into the hub. The pipe end is inserted into the socket until it seats on the shoulder, then pulled back approximately 1/16" (1.6 mm) before a single fillet weld is applied on the outside of the hub. This inward shoulder acts as a built-in pipe stop: it ensures consistent insertion depth, keeps the pipe centred during welding, and eliminates the need for pipe-end beveling.

Socket weld flanges to ANSI/ASME B16.5 are typically specified for smaller pipe sizes - NPS ½" through 3" - in pressure classes where a full butt-weld joint is unnecessary but a stronger, more fatigue-resistant connection than a slip-on is required. Because the weld is made entirely on the outside of the pipe without penetrating the bore, socket weld flanges are faster to install than weld neck flanges and do not require radiographic inspection in most service codes.
(From our production experience: The single most common socket weld failure we see in returned samples is a missing expansion gap - the pipe was butted flush against the shoulder before welding. Under thermal cycling, the weld toe cracks. Always pull the pipe back 1.6 mm before tacking.)

Socket weld flanges are the right choice when all three of the following conditions are met: the pipe is NPS 3" or smaller; the process fluid is non-corrosive (or at least not crevice-sensitive); and the service does not require full radiographic inspection of the flange-to-pipe weld. In those conditions they offer a compact, cost-effective alternative to weld neck flanges without the alignment complexity of slip-on connections.

They are not recommended for corrosive fluids, radioactive media, food or pharmaceutical clean-steam lines, or any service where the annular crevice between the pipe OD and the counterbore cannot be tolerated. In those cases, specify a weld neck flange with a full-penetration butt weld.
(Not recommended for: corrosive media, clean-steam / food / pharma lines, radioactive service, or pipe sizes above NPS 3". If in doubt, upgrade to weld neck - the price difference is small and the lifecycle cost is lower.)

All grades are produced by open-die or closed-die hot forging to ASTM A182, with material test reports (EN 10204 3.1) issued for every heat. We do not supply cast socket weld flanges - forged grain structure is essential for fatigue resistance in small-bore high-pressure connections.

For full chemical composition, mechanical properties and corrosion data, see our Material Data Sheet 

You must specify the pipe schedule when ordering. Socket weld flanges are machined to match a specific pipe OD - a Class 150 NPS 2" SCH 40 flange cannot accept SCH 80 pipe without bore mismatch. If unsure, send us your pipe mill certificate and we will confirm the correct schedule.

Socket weld flanges in ASME B16.5 are most commonly supplied with a raised face (RF). The raised face is a 1/16" (1.6 mm) high ring surrounding the bore that concentrates gasket seating load. A flat face (FF) is used when the mating flange is cast iron or non-metallic - using RF against FF cast iron generates bending stress that can fracture the iron flange. RTJ is available for Class 600 and above where metal ring gaskets are specified.

Socket weld flanges are most valuable in applications where pipe size is small, the piping layout is congested, and repeated make-and-break connections are not required. The counterbore socket eliminates the pipe-to-flange alignment problem that makes small-bore slip-on flanges difficult to weld in tight spaces.

In the chemical and petrochemical industry, they are the standard choice for instrument impulse lines, sampling points, chemical injection quills, and drain and vent connections - all typically NPS 1" to 2" in Class 300 or 600. The compact flange OD matters here: a Class 600 NPS 2" socket weld flange fits in spaces where a weld neck would require redesigning the pipe rack.

In oil and gas facilities, socket weld flanges appear on wellhead chemical injection lines, metering skid connections, and the small-bore utility headers feeding instrument air and purge gas. Duplex 2205 is the standard grade for offshore installations where seawater exposure makes SS316L borderline.

Power generation plants specify Class 600 and 900 socket weld flanges for high-pressure condensate, drain and blow-down lines in the steam turbine auxiliary systems - typically in SS321 or SS310 at temperatures above 400°C. The small bore size keeps the fillet weld manageable even in restricted boiler room access.

 

Socket Weld vs Other Flange Types

 

Criterion	Socket Weld	Slip-On	Weld Neck
Weld type	1 external fillet	2 fillet welds	Full butt weld
Radiographic inspection	Not required in most codes	Not required	Often required
Pipe beveling	Not required	Not required	Required
Fatigue resistance	Better than slip-on	Lowest - two fillet welds	Best
Crevice	Yes - expansion gap crevice	Yes - annular gap	None
Size range	NPS ½" – 3" standard	NPS ½" – 24" / ½"–24"	NPS ½" – 24" / ½"–24"
Clean / pharma service	Not recommended	Not recommended	Recommended
Cost vs weld neck	Lower	Lowest	Higher

 

FAQ

 

Q: Why must I specify the pipe schedule when ordering a socket weld flange?

A: The counterbore of a socket weld flange is machined to match the outside diameter of a specific pipe schedule. If you fit a SCH 40 pipe into a flange bored for SCH 80, there is an annular step at the socket shoulder - turbulence, erosion and corrosion initiate exactly there. If you force a SCH 80 pipe into a SCH 40 bore, it simply will not go. Unlike slip-on or weld neck flanges where the bore can accommodate a range of pipe dimensions, socket weld flanges require an exact match. If you are unsure of your pipe schedule, provide the pipe OD and wall thickness, and we will machine the correct bore.

Q: What is the correct expansion gap and what happens if I skip it?

A: ASME B31.3 specifies the pipe end should be retracted approximately 1/16" (1.6 mm) from the socket shoulder before welding. This gap prevents the pipe from bearing against the shoulder during the thermal expansion of welding and subsequent thermal cycles in service. If the gap is omitted, the pipe bears against the shoulder, the fillet weld root is loaded in tension, and fatigue cracking initiates at the weld toe within a relatively small number of thermal cycles. This is the most common mechanism of socket weld failure. A simple spacer rod or depth gauge ensures the gap is consistent.

Q: Can socket weld flanges be used with stainless steel piping in chemical service?

A: It depends on the process fluid. For non-corrosive or mildly corrosive fluids where the small crevice at the expansion gap is not a concern, socket weld flanges in SS304 or SS316L are entirely appropriate. However, for highly corrosive media - sulfuric acid, hydrochloric acid, concentrated caustic, seawater injection - the crevice between the pipe OD and the counterbore traps stagnant fluid that cannot be flushed. Even SS316L will corrode in a tight, stagnant gap with the right chemistry. For those services, specify weld neck flanges with full-penetration butt welds. Our SS316L socket weld flanges are widely used in instrument impulse lines, small-bore drain and vent connections, and chemical injection points where the pipe ID is fully swept by flowing fluid.

Q: What is the maximum pressure class available for stainless steel socket weld flanges?

A: ASME B16.5 covers socket weld flanges through Class 2500 in stainless steel grades. In practice, Class 1500 and 2500 socket weld flanges are specialty items - at those pressure levels, the bore tolerances become extremely tight, the hub wall is very thick, and weld quality requires strict procedure qualification. We supply Class 150 through Class 900 from stock or short-order production. Class 1500 and 2500 require 4–6 weeks lead time and are produced to a witnessed inspection protocol. If your application requires Class 1500 or 2500, contact us early with your full specification.

Hot Tags: stainless steel socket weld flange, China stainless steel socket weld flange manufacturers, suppliers, factory, 3 4 threaded flange, blind flange 2, dn 50 pn16, asme b16 5 150 flange dimensions, asme b16 5 300, flange dn 200 pn 10