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Slip-On Flanges | SO Flanges for Low & Medium Pressure Piping - Sunny Steel Industrial Pipe Product

Slip-On Flanges

SO Flanges for Low & Medium Pressure Piping

Slip-on flanges (SO) feature a simple slip-over design, welded inside and outside for secure connections. Ideal for low-to-medium pressure applications and general industrial piping.

Slip on flange, also called SO flange. It's a kind of flange slides over the pipe with internal design is slightly larger than the pipe. Since the inner diameter of the flange is slightly larger than the outer diameter of the pipe, the SO flange can be directly connected to equipment or pipe by fillet weld at the top and bottom of the flange. It is used to insert the pipe into the inner hole of the flange. Slip-On Pipe Flanges. As made obvious by their name, these pipe flanges slip over the pipe. They're manufactured with an inside diameter that is slightly bigger than the pipe's outside diameter. These attachments are connected to the pipe via fillet weld at the top and bottom of the flange.

Types of Slip On Flange Welding

The SO flange can be divided into SO welding plate flange and SO welding hubbed steel pipe flange. Its mechanical characteristics are between the integral flange and the looping flange. The structure is simple, and the processing is convenient. So slip on flange welding is widely used in various fluid pipelines.

Depends on different face, there are also ranges raised face type and ring type joint face type.

Raised Face Slip On Flange

Raised Face Slip On Flange

There is a small portion extruded from the bottom face of the slip on flange, this type is raised face slip on flange. The function of this area is to place a gasket seat during installation to get a better sealing performance.

As the pressure ratings bigger, the height of this raised face will be bigger.

RTJ Slip on Flange

RTJ Slip on Flange

A small grooved is machined on the raised face part, this form is called RTJ type, the function of this groove is to place the gasket ring, also applied for sealing, compared to RF type, RTJ is designed for high pressure use.

Slip on flange use slip welding to connect equipment, so either below of name is describing the same flange:

  • Slip on weld flange
  • Slip on flange weld
  • Weld slip on flange
  • Slip on flange welding
  • SO flange

Manufacturing Types

Slip on flange can be made by forging, steel cutting, casting and etc. Among these manufacturing types, the forging type gains the best quality and also the most common use, price is higher than other types. So before purchase the slip on flange, you have to know what is the specific working environment.


Advantages of Slip On Flange

Weldneck and Slip-On Orifice Runs

Slip-On flanges or SO flanges are commonly lower in price than weld-neck flanges, and to this effect are a popular choice for our customers.

  • Lower installation costs
  • More easy to align with other parts during installation
  • Better leaking proof
  • ​Inner and outer welding on flange
  • Takes less time to cut accurately for the pipelines
  • As pipe slides on the flange, it compatible with lower hub on slip on flange

Slip On Flange vs Weld Neck Flange

  • The strength for internal pressure of Slip On Flange is two-thirds of Weld Neck Flange.
  • Durability life is 1/3 of WN flange.
  • 2 fillet welding required for SO flange, one inside and one outside of flange.
  • A space shall be reserved between the end of the pipe and the end of the flange during welding work, to avoid damage the flange face.
  • Slip on flange has to connect with a pipe firstly, then connect a fitting. (Combination of flange+elbow, or flange+tee not available, since the fittings not in a straight end, it can not slide completely into the flange bore. )

Slip on flange are usually cheaper than Weld-Neck flange (welding neck flange), which is why many customers prefer to choose them. It is one of the commonly used flanges for low pressure, medium temperature piping system.

On the other hand, since the flange bore is larger than the pipe diameter, it usually requires more welding work than the other flanges. So the durability is not as long as the welding neck flange, all of these factors should be considered before choose a right flange.


Why it is called slip on flange?

A slip-on flange's bore size (internal diameter) is larger than that of the connecting pipe, which allows it to slide/slip onto the pipe (slip-onto the pipe). There is no full penetration weld between the pipe and the flange, thus there are limitations for its usage due to lower weld integrity.


Slip-on flange datasheets

The datasheets we have on this site are shown below. For simplicity sake, only datasheets that adhere to B16.5 are shown. ASME B16.5 covers flange dimensions from ½" to 24". For sizes larger than this, please visit our flange datasheets page.

Class Flat Face Raised Face Ring Type Joint
ANSI 150 SO Flange ANSI 150 FF (in) SO Flange ANSI 150 RF (in) SO Flange ANSI 150 RTJ (in)
ANSI 300 SO Flange ANSI 300 FF (in) SO Flange ANSI 300 RF (in) SO Flange ANSI 300 RTJ (in)
ANSI 400 SO Flange ANSI 400 FF (in) SO Flange ANSI 400 RF (in) SO Flange ANSI 400 RTJ (in)
ANSI 600 SO Flange ANSI 600 FF (in) SO Flange ANSI 600 RF (in) SO Flange ANSI 600 RTJ (in)
ANSI 900 SO Flange ANSI 900 FF (in) SO Flange ANSI 900 RF (in) SO Flange ANSI 900 RTJ (in)
ANSI 1500 SO Flange ANSI 1500 FF (in) SO Flange ANSI 1500 RF (in) SO Flange ANSI 1500 RTJ (in)
ANSI 2500 SO Flange ANSI 2500 FF (in) SO Flange ANSI 2500 RF (in) SO Flange ANSI 2500 RTJ (in)

Why slip on flanges are preferred to welding neck flanges

For many users, slip on flanges continue to be preferred to welding neck flanges because of the following reasons:

  • On account of their initially lower cost.
  • The reduced accuracy needed in cutting the pipe to length.
  • The greater ease of alignment of the assembly.
  • The calculated strength of slip-on flanges under internal pressure is approximately two-thirds that of welding neck flanges.

How to measure slip-on flanges

Tied universal expansion joint applications

Take the measurements of:

  • OD: Outside Diameter
  • ID: Inside Diameter
  • BC: Bolt Circle
  • HD: Hole diameter

Key Features

Some important features are as follows:

  • One size fits all pipe schedules.
  • Fabricators can more easily cut pipe to length for slip-on flanges.
  • The smaller thickness of this flange allows for easier alignment of bolting holes.
  • They are generally not preferred for high pressure temperature environments.

Pressure Class & Nominal Pressure

Pressure ratings define the maximum operating pressure a flange can withstand at a given temperature. American standards use “Class” ratings, while European standards use “PN” (nominal pressure). Our slip-on flanges cover all common pressure grades.

ANSI Class Equivalent PN Rated Pressure (Bar) Typical Application
Class 150 PN16 16 Water, gas, fire protection, HVAC
Class 300 PN40 40 Medium-pressure process pipelines, cooling water
Class 600 PN63 63 High-pressure utility lines, chemical processing
Class 900~1500 PN100~PN160 100~160 Special high-pressure industrial applications

Class 150 (PN16) is the most common rating for slip-on flanges, suitable for the majority of low-pressure industrial and commercial applications. Higher classes are available for more demanding service conditions.

Flange Material

Materials

Pipe flanges are manufactured in all the different materials like stainless steel, cast iron, aluminium, brass, bronze, plastic etc. but the most used material is forged carbon steel and have machined surfaces.

Flanges are welded to pipe and equipment nozzle. Accordingly, it is manufactured from the following materials;

  • Carbon steel
  • Low alloy steel
  • Stainless steel
  • Combination of Exotic materials (Stub) and other backing materials

The list of materials used in manufacturing is covered in ASME B16.5 & B16.47.

  • ASME B16.5 -Pipe Flanges and Flanged Fittings NPS ½” to 24”
  • ASME B16.47 -Large Diameter Steel Flanges NPS 26” to 60”

Commonly used Forged material grads are

  • Carbon Steel: – ASTM A105, ASTM A350 LF1/2, ASTM A181
  • Alloy Steel: – ASTM A182F1 /F2 /F5 /F7 /F9 /F11 /F12 /F22
  • Stainless Steel: – ASTM A182F6 /F304 /F304L /F316 /F316L/ F321/F347/F348

Frequently used astm grades

Material Fittings Flanges Valves Bolts & Nuts
Carbon Steel A234 Gr WPA A105 A216 Gr WCB A193 Gr B7
A194 Gr 2H
A234 Gr WPB A105 A216 Gr WCB
A234 Gr WPC A105 A216 Gr WCB
Carbon Steel
Alloy
High-Temp
A234 Gr WP1 A182 Gr F1 A217 Gr WC1 A193 Gr B7
A194 Gr 2H
A234 Gr WP11 A182 Gr F11 A217 Gr WC6
A234 Gr WP12 A182 Gr F12 A217 Gr WC6
A234 Gr WP22 A182 Gr F22 A217 Gr WC9
A234 Gr WP5 A182 Gr F5 A217 Gr C5
A234 Gr WP9 A182 Gr F9 A217 Gr C12
Carbon Steel
Alloy Low-Temp
A420 Gr WPL6 A350 Gr LF2 A352 Gr LCB A320 Gr L7
A194 Gr 7
A420 Gr WPL3 A350 Gr LF3 A352 Gr LC3
Austenitic Stainless Steel A403 Gr WP304 A182 Gr F304 A182 Gr F304 A193 Gr B8
A194 Gr 8
A403 Gr WP316 A182 Gr F316 A182 Gr F316
A403 Gr WP321 A182 Gr F321 A182 Gr F321
A403 Gr WP347 A182 Gr F347 A182 Gr F347

ASTM standards define the specific manufacturing process of the material and determine the exact chemical composition of pipes, fittings and flanges, through percentages of the permitted quantities of carbon, magnesium, nickel, etc., and are indicated by "Grade".

The usual materials of flanges include stainless steel, carbon steel, aluminum and plastic. The choice of the material largely depends on the purpose of the flange. For example, stainless steel is more durable and is necessary for heavy use. On the other hand, plastic is more feasible for use in the home because of its reasonable price and easy installation. The materials used for flanges are under the designation of the American Society of Mechanical Engineers.


Flange materials acc. to ASTM

The most common materials for pipe flanges (forged grades) are: ASTM A105 (carbon steel high temperature to match A53/A106/API 5L pipes), A350 Grades LF1/2/3 (carbon steel low temperature to match A333 pipes), A694 Grades F42 to F80 (high yield carbon steel to match API 5L pipe grades), ASTM A182 Grades F5 to F91 (alloy steel flanges to match A335 pipes), A182 Grade F304/316 (stainless steel flanges to match A312 SS pipes), A182 Gr. F44/F51/F53/F55 (duplex and super duplex to match A790/A928 pipes) and various nickel alloy grades (Inconel, Incoloy, Hastelloy, Monel).

The material qualities for these flanges are defined in the ASTM standards.


What are ASTM Grades?

For example, a carbon steel pipe can be identified with Grade A or B, a stainless-steel pipe with Grade TP304 or Grade TP321, a carbon steel fitting with Grade WPB etc.

Standard
Pipe Flange Standards mainly include three systems in the world, ANSI/ASME flange system(American), DIN flange system(European system), JIS flange system, other system made according to this three systems, like GB flange standard, which mainly made according to ANSI/ASME and DIN flange standard, Duwa Piping supplies those flanges with top quality and soonest delivery time.

  • ASME B16.1 – Gray Iron Pipe Flanges and Flanged Fittings: Classes 25, 125, and 250

  • ASME B16.5 – Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard

  • ASME B16.20 – Ring Joint Gaskets and Grooves for Steel Pipe Flanges

  • ASME B16.21 – Nonmetallic Flat Gaskets for Pipe Flanges

  • ASME B16.24 – Cast Copper Alloy Pipe Flanges and Flanged Fittings: Classes 150, 300, 600, 900, 1500, and 2500

  • ASME B16.34 – Large Diameter Steel Flanges (NPS 26 through NPS 60)

  • ASME B16.36 – Orifice Flanges

  • ASME B16.42 – Ductile Iron Pipe Flanges and Flanged Fittings: Classes 150 and 300

  • ASME B16.47 – Large Diameter Steel Flanges (NPS 26 Through NPS 60)


  • ASTM A105 – Specification for Carbon Steel Forgings for Piping Applications

  • ASTM A182 – Specification for Forged or Rolled Alloy Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High Temperature Service

  • ASTM A193 – Specification for Alloy Steel and Stainless Steel Bolting Materials for High Temperature Service

  • ASTM A194 – Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure and High Temperature Service

  • ASTM A694 – Specification for Carbon and Alloy Steel Forgings for Pipe Flanges, Fittings, Valves, and Parts for High-Pressure Transmission Service

  • ASTM A707 – Specification for Flanges, Forged, Carbon and Allow Steel for Low Temperature Service


  • AWWA C115 – Standard for Flanged Ductile Iron Pipe with Ductile-Iron or Gray-Iron Threaded Flanges


  • ISO 5251 – Stainless steel butt-welding fittings


  • MSS SP-6 – Standard Finishes for Contact Faces Pipe Flanges and Connecting End Flanges of Valves and Fittings

  • MSS SP-9 – Spot Facing for Bronze, Iron and Steel Flanges

  • MSS SP-25 – Standard Marking Systems for Valves, Fittings, Flanges, and Unions

  • MSS SP-44 – Steel Pipeline Flanges

  • MSS SP-53 – Quality Standards for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Components – Magnetic Particle

  • MSS SP-54 – Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components – Radiographic

  • MSS SP-55 – Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components – Visual

  • MSS SP-75 – High Test Wrought Butt Welding Fittings

  • MSS SP-106 – Cast Copper Alloy Flanges and Flanged Fittings Class 125,150, and 300

  • ASME B16.5 and ASME B16.47 cover pipe flanges up to NPS 60 (B16.5 from 1/2″ to 24″ and B16.47 from 26″ to 60″). ANSI

  • B16.47 covers two series of flanges, Series A is equal to MSS SP-44-44, and Series B is equal to API 605 (API 605 has been canclled).

Application of flanges

Applications

A flange is a method of connecting pipes, valves, pumps, and other equipment to form a piping system. It also provides easy access for cleaning, inspection, or modification.

When a piping joint requires to be dismantled, flanges are being used. These are primarily used on equipment, valves, and specialty items. Breakout flanges are provided at predetermined intervals in certain pipelines where maintenance is a regular occurrence. The flanges, gaskets, and bolting make up a flanged joint, which is made up of three separate but interconnected components. To achieve a leak-proof joint, special controls are required in the selection and application of all of these elements.

Here are the details of Flanges about their advantages and their applications.

Advantages of Flanges

Pipes, valves, pumps, and other parts are connected with flanges to form a piping system. Generally, flanges are welded or screwed together. The use of flanges makes pipe system maintenance and repair a breeze. Instead of taking the entire pipe for inspection, a small section of the pipe can be carefully investigated to use a flange to locate the fault.

The following are the five most important benefits of The following are the five most important benefits of flanges:

  • Easy assembly in tight spaces where wrenches may not have clearance if traditional flange fittings are used. With moderate torque, they’re easier to put together.
  • In hard-to-reach areas where flexibility is required, adapters in the hose line, pipe, or tube can be removed.
  • Pipe connections, tubes, or large hose links with high pressure, vibration, or shock pressures that could damage traditional large hydraulic fittings more easily.
  • In rigid lines such as metal tubes or continuous pipes, making connections allows for easy maintenance.
  • In demanding hydraulic applications, reduce the chance of components becoming loose.

A flange is a method of connecting pipes, valves, pumps, and other equipment to form a piping system. It also provides easy access for cleaning, inspection, or modification. Flanges are usually welded or screwed.

In many applications, engineers need to find a way to close off a chamber or cylinder in a very secure fashion, usually because the substance inside must differ from the substance outside in composition or pressure.

They do this by fastening two pieces of metal or other material together with a circle of bolts on a lip. This “lip” is a flange.


Plumbing

You can connect two sections of metal piping by soldering or welding them together, but pipes connected in this way are very susceptible to bursting at high pressures. A way of connecting two sections of pipe more securely is by having flanged ends that you can connect with bolts. This way, even if gases or liquids build up to high pressures inside the pipe, it will often hold with no problem.


Mechanics

In order to connect two sections of a large, enclosed area, it is often best to used flanges and bolts. An example of this is the connection between the engine and the transmission in an automobile. In this case, both the engine and the transmission contain a number of moving parts that can easily get damaged if they get dust or other small objects inside of them. By connecting the outer casings of the engine and transmission in this way, engineers protect the inner workings of both.


Electronics

Flanges have a specific purpose in cameras and other electronic devices. Though flanges in such items do not usually have to sustain high pressures, they do have to hold tight so they can keep out harmful particles. These flanges are usually found connecting two different materials, such as the glass of a lens and the rest of the body of the camera.

Delivery

Steel flanges must be packed with seaworthy packing method then delivery to customers, usually the packing way include wooden box, wooden pallet, iron & steel cage, iron & steel pallet etc.

Flange Marking

Flange Marking

Flange markings are governed by ANSI ASME codes. Flange marking includes;

  • Manufacturer logo
  • ASTM material code
  • Material Grade
  • Service rating (Pressure-temperature Class))
  • Size
  • Thickness (Schedule)
  • Heat No
  • Special marking if any QT (Quenched and tempered) or W (Repair by welding)

PMI-raw material inspection

Flange raw material PMI
Flange raw material PMI
Flange raw material PMI

Size inspection

ASME B16.5 and B16.47 standards cover permissible tolerances for inspection.

Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection

Packing

Because of the normal wooden boxes or wooden pallets have to do fumigation treatment, we usually use plywood pallet or plywood case or box to pack steel flanges without fumigation treatment.

Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection
Flange size inspection
Frequently Asked Questions
A slip-on flange (SO flange) is a common pipe flange that slides over the pipe end and is secured with internal and external fillet welds. It is designed for low-to-medium pressure applications.
They are easy to install, cost-effective, versatile in materials, and suitable for tight spaces. No pipe beveling is required, saving time and labor.
Weld neck flanges have a long tapered hub and require butt welding, offering high strength for high-pressure service. Slip-on flanges slide over the pipe, use fillet welds, and are cheaper but less strong.
Our slip-on flanges meet ASME B16.5, ASME B16.47, DIN 2573/2576, BS 4504 and JIS B2220 standards for global project compatibility.
We offer carbon steel (ASTM A105), stainless steel (304/304L, 316/316L), alloy steel (F11/F22) and duplex steel for various service conditions.
We provide ANSI Class 150, 300, 600, 900, 1500 and corresponding PN ratings (PN16 to PN160) for low to high pressure applications.
Standard types are Raised Face (RF) and Flat Face (FF). Ring Type Joint (RTJ) is available for special high-pressure requirements.
Slide the flange onto the pipe, ensure proper pipe extension, tack weld, then weld outside and inside. Clean the face, add gasket, align bolts and tighten evenly in a crisscross pattern.
They are widely used in water/wastewater, HVAC, petrochemical, power generation, food processing and general industrial piping systems.
Yes. We can customize non-standard sizes, thicknesses, bolt patterns, materials and markings according to your drawings and specifications.
Slip-on flanges are primarily designed for low-to-medium pressure applications (Class 150/300). For high-pressure or cyclic loading, weld neck flanges are recommended.
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