Socket Weld Flange

Socket weld flange is usually suitable for smaller high-pressure pipelines and are connected to the pipeline through socket welding. It allows for a smooth bore and better flow of the gas or fluid inside the pipe. It is  usually provided with an RTJ facing, flat face, or raised face. Socket weld flange initially designed for high pressure small diameters piping system. Moreover, apply for projects such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, self-control, etc.

Features of Socket Weld Flanges:

Connection Type: The pipe is inserted into the flange’s socket and then fillet welded around the outer joint.

Alignment: Provides good alignment of the pipe and flange bore.

Strength: Offers better fatigue resistance compared to slip-on flanges due to the weld’s geometry.

Usage: Typically used in high-pressure systems, especially in chemical processing, oil and gas, and steam applications.

Properties of Socket Weld Flanges

Socket weld flanges are characterized by their recessed socket design that simplifies pipe alignment for welding with a single external fillet weld, making them suitable for low to medium pressure applications and smaller pipe sizes where ease of installation and a relatively smooth bore are beneficial. One of the significant benefits of socket weld flanges is that they offer excellent flow rates due to their smooth bore transition from the pipe into the flange. They can also handle high-pressure situations, making them an ideal choice for various applications.

Composition of Socket Weld Flanges

Socket weld flanges are manufactured from a variety of materials including carbon steel, stainless steel, alloy steel, duplex and super duplex stainless steel, nickel alloys, copper alloys, and titanium, with the specific material grade selected based on the intended service conditions, such as pressure, temperature, and the corrosive nature of the conveyed media and environment.

Material for Forged Steel Flange

We are specialized in various steel flanges, the materials including carbon steel, alloy steel and stainless steel.

Carcon Steel: ASTM A105 / A105N,ASTM A350 LF2 / LF3, A694 F42 / 46 / 52 / 56 / 65 / 70

Alloy Steel: ASTM A182 F5 / F9 / F11 / F12 / F22 / F91 / F92

Stainless Steel: A182 F304/304L/304H – F316/316L – F317 – F310S – F321 – F347 – F904L

Duplex Stainless Steel: A182 F51/53/55/60

Copper Alloy: UNS No. C 10100, 10200, 10300, 10800, 12000, 12200, 70600, 71500, UNS No. C 70600 (Cu -Ni- 90/10), C71500 (Cu -Ni- 70/30)

Nickel Alloys: Nickel 200 (UNS No. N02200), Nickel 201 (UNS No. N02201), Monel 400 (UNS No. N04400), Monel 500 (UNS No. N05500), Inconel 800 (UNS No. N08800), Inconel 825 (UNS No. N08825), Inconel 600 (UNS No. N06600), Inconel 625 (UNS No. N06625), Inconel 601 (UNS No. N06601), Hastelloy C 276 (UNS No. N10276), Alloy 20 (UNS No. N08020), Titanium (Grade I & II).

Common Socket weld flanges standards

ASME/ANSI B16.5: This is the main standard covering pipe flanges and flanged fittings, including socket weld flanges, for sizes from 1/2″ to 24″. It specifies dimensions, materials, pressure-temperature ratings, and testing requirements.

ASME B16.47: This standard covers large diameter steel flanges from NPS 26″ to NPS 60″.

SAE J518 / ISO 6162: These standards apply to socket weld SAE flanges, which are hydraulic flanges used in oil hydraulic systems.

DIN Standards: For example, DIN 2576 PN10 specifies dimensions for plate flanges, including those that can be socket welded.

Socket Welded Flange Face Types

Socket welded flange including RF type and RTJ type, which like other types of welding flanges (slip on, weld neck or blind flange).

RF 

RF socket weld flange has a small portion surrounding the flange bore that protrudes from the face. Gasket seat will be placed in this raised area.

RTJ

On the raised face surface there has a groove is RTJ type, which you can place a gasket ring to get better sealing performances.

Common Types of Coatings Applied to Socket Weld Flanges

Coatings are frequently applied to socket weld flanges for several reasons, primarily for corrosion protection but also for identification or aesthetic purposes. The specific type of coating depends on the flange material, the service environment, and project requirements.

1. Anti-Rust Coatings (Primers and Paints):

Black Paint: A common and cost-effective coating for general atmospheric corrosion protection during storage and transportation. It offers mild protection.

Epoxy Coatings: Offer excellent resistance to chemicals, moisture, and abrasion. They create a durable and long-lasting protective layer, suitable for more aggressive environments like chemical processing plants.

2. Galvanizing:

Electro Zinc Plating (Cold Galvanizing): A thin layer of zinc is applied electrolytically. Offers moderate corrosion resistance and is often used for less severe environments. Can be silvery white or golden in color.

Hot-Dip Galvanizing: A thicker layer of zinc is applied by immersing the steel flange in molten zinc. Provides superior and long-lasting corrosion protection, especially in outdoor and marine environments.

3. Specialized Coatings:

PTFE (Teflon) Coatings: Used for excellent chemical resistance, especially to acids and alkalis.

PEEK, PFA, PVDF Coatings: Other fluoropolymer coatings offering specific chemical and temperature resistance properties.

Passivation: A process used for stainless steel flanges to enhance the natural chromium oxide layer on the surface, improving corrosion resistance.

Markings

ASME B16.5 flange shall furnished with below marking requirements.

Name: Manufacturer name or trademark

Material: Material standard ASTM A105/ASTM A182/ASTM A694 etc.

Pressure Ratings: Class 150 to 2500

Conformance: ASME B16.5 /EN standard/other standard

Size: Diameter and pressure or thickness

Marking: 1″ CL150 SW RF A182 F316 ASME B16.5 ZZ12586

✅ Advantages of SW Flanges

Easy Installation

Good for Small Pipe Sizes

Leak-Proof Connection

Strong and Reliable

Cost-Effective Welding

No Need for Beveling the Pipe

❌ Disadvantages of SW Flanges

Not for Corrosive or Radioactive Fluids

Weld Defect Risk

Inspection Limitations

Not Ideal for Large Pipe Sizes

Gap Requirement

Socket Weld Flange vs Slip-On Flange

Feature	Socket Weld Flange	Slip-On Flange
Welding Type	Fillet weld only on the outside	Fillet weld on both inside and outside
Pipe Insertion	Pipe is inserted into a recessed socket	Pipe passes through the flange face
Strength	Stronger – better fatigue and pressure resistance	Weaker – lower fatigue resistance
Best For	High pressure, small diameter pipes (≤ 2″)	Low-pressure, large diameter systems
Preparation	No need to bevel pipe ends	No need to bevel pipe ends
Alignment	Easier due to socket – good alignment	Less precise – pipe can move before welding
Cost	Slightly more expensive due to design	Lower initial cost and easier to install
Weld Inspection	Harder to inspect (only surface methods)	Easier to inspect (both welds visible)
Corrosion Risk	Risk of crevice corrosion in socket	Less risk of fluid trap (depends on weld quality)

Uses of Socket Weld Flanges

High-Pressure Piping Systems

Small-Diameter Piping (≤ 2 inches)

Steam, Oil, Gas, and Water Lines

Chemical Processing Plants

Power Plants

Petrochemical and Oil Refineries

Shipbuilding and Marine Applications

Food & Beverage and Pharmaceutical Plants (occasionally)

Frequently Asked Questions (FAQs)

1. when should I use socket weld flange？

Socket weld flanges are used for high-pressure, smaller diameter piping systems (typically under 2-4 inches) where a strong and leak-resistant connection is needed, especially in applications with space constraints or as a robust alternative to threaded connections, benefiting from easier alignment during installation and not requiring pipe beveling.

2. How do I install a socket weld flange？

To install a socket weld flange, insert the pipe into the flange’s socket until it reaches the bottom, then pull it back approximately 1/16 inch (1.5 mm) to create an expansion gap before applying a fillet weld around the top outside edge of the socket to secure the pipe to the flange.

3. What is the difference between cast flange and forged flange?

Molten metal forms cast flanges by pouring. They are low-cost and suitable for complex shapes, but they may contain pores or impurities inside and have slightly weaker strength. They are mostly used in low-pressure, non-critical occasions.

High-temperature forging makes metal flanges. They have a dense structure, high strength, pressure resistance and impact resistance. They are suitable for high pressure, high temperature or harsh environments, but they are more expensive.