Flange Selection Guide
At OneHydraulics, we know that there are many styles of flange to choose from, and it's not always clear why you may use
one style over another. We've compiled the guide below to make your flange selection just a bit easier.
This guide compares five flange styles by how they attach to tube or pipe: butt weld, socket weld, saddle weld, captive and split. Choose the attachment style first, then match the pressure class. SAE J518 Code 61 flanges are rated 3,000 psi and Code 62 flanges 6,000 psi. To confirm which code a port is, see the Adapter & Thread Identification Guide, browse all flanges, or call 281-941-2310.
Butt Weld Flanges
Butt weld connections allow the pipe to ‘butt’ against the end of the flange. The two pieces are then welded around the outside beveled perimeter.
Butt weld connections are often favored over socket weld connections since there is greater weld penetration which results in a stronger connection.
Socket Weld Flanges
Socket weld connections allow the pipe to slip inside the socket of the flange. The connection is then welded at the base of the connection where the pipe makes a
90 degree connection with the flange. While the weld penetration is not as deep as would be with a butt weld connection, it is often favored because it is easier to weld.
Saddle Weld Flanges
Saddle weld flanges are used to ‘tap into’ an existing piece of pipe or new pipe assembly to create a new flange connection port.
The existing pipe must be drilled in the appropriate location and cleaned to remove any debris or metal shavings.
The saddle weld flange is then placed over the hole and welded around the perimeter.
Captive Flanges
Captive flange are available with either drilled bolt holes for o-ring side connections or tapped bolt holes for flat face side connections.
They are often used on new tube or pipe assemblies because they are confined to the assembly and will not be lost when the equipment is serviced in the future.
Split Flanges
Split flanges are only available with drilled holes and is simply a captive flange that is drilled in half. They are preferred for most o-ring flange head
connections because of their ease of assembly and disassembly. They are commonly used with hose and split flange adapter fittings (flange heads)
because it is often not possible to fit a captive flange over the outside diameter of the fittings. Split flange simply slide around from the outside.
Frequently Asked Questions
What is the difference between a butt weld and a socket weld flange?
On a butt weld flange, the pipe butts against the end of the flange and the two pieces are welded around the outside beveled perimeter. On a socket weld flange, the pipe slips inside the flange socket and is welded at the base, where the pipe meets the flange at 90 degrees. Butt weld connections are often favored because the deeper weld penetration gives a stronger connection. Socket weld connections are often chosen because they are easier to weld.
When should I use a saddle weld flange?
Use a saddle weld flange to tap into an existing pipe, or a new pipe assembly, and create a new flange port. Drill the pipe in the right location, clean out any debris and metal shavings, place the saddle weld flange over the hole, and weld it around the perimeter.
What is a captive flange?
A captive flange is a one-piece flange that stays confined to the tube or pipe assembly, so it cannot be lost when the equipment is serviced later. That makes it a common choice on new tube and pipe assemblies. Captive flanges come with drilled bolt holes for the O-ring side of a connection or tapped bolt holes for the flat face side.
What is a split flange, and why is it used with hose?
A split flange is a captive flange cut in half, and it is only available with drilled bolt holes. The two halves slide around the fitting from the outside, so they can be used where a one-piece captive flange will not fit over the outside diameter of the fitting. That is why split flanges are common with hose and with split flange adapter fittings (flange heads), and why they are preferred for most O-ring flange head connections: they are easy to assemble and disassemble.
Should I choose a split flange or a captive flange?
Choose a captive flange for new tube or pipe assemblies where you want the flange to stay with the assembly through future service. Choose a split flange when the flange has to go on around a hose end or flange head that a one-piece flange cannot pass over, or when the connection will be taken apart often.
What is the difference between drilled and tapped bolt holes on a flange?
Drilled holes are plain through-holes, used on the O-ring side of the connection, where bolts pass through the flange and thread into the mating port or flange. Tapped holes are threaded, used on the flat face side, so the flange itself receives the bolts. Captive flanges come either way. Split flanges are only made with drilled holes.
What is the difference between Code 61 and Code 62 flanges?
Both are SAE J518 4-bolt flanges with the same overall design. Code 61 is the standard 3,000 psi flange, and Code 62 is the 6,000 psi flange for higher pressure. Code 62 flanges have larger flange head diameters and bolt hole spacing, so the two codes do not interchange. Match the flange code to the port.
How does a 4-bolt hydraulic flange seal?
The port is smooth and unthreaded, with four bolt holes in a rectangular pattern around it. The flanged head has a groove for an O-ring. The seal is made where the O-ring is compressed between the flanged head and the flat surface of the port, and threaded bolts through the split or captive flange hold the connection together.