RFSO Flange
RFSO Flange
What is a slip on (RFSO) flange?
RFSO stands for raised face slip-on. The raised face is the gasket seating area, raised above the bolting face. Slip-on means the flange slides over the end of the pipe and is then welded on both the inside and the outside.
In EN1092-1 this is the type 01 plate flange for welding. In ANSI B16.5 it’s the slip-on form.
How is an RFSO flange fitted?
The flange slides over the pipe end, is aligned with the matching flange, and is then fillet welded on the inside and the outside. Two welds hold it in place, which is why slip-on flanges are described as double welded.
Because the pipe passes into the flange rather than being butt welded to it, alignment is easier than with a weld neck. That ease of fitting is a large part of why they’re so popular.
What are the strengths and limits of slip-on flanges?
Slip-on flanges are cheap, popular and easy to install, which keeps costs down on a project. They’re also thinner than most other flange types.
Slip-on is one of several flange types, and each strikes a different balance between cost, strength and ease of fitting. The trade-off is that slip-ons are best used in low-pressure, low-temperature applications. For demanding duties, a weld neck is the better choice, and our RFWN flanges are built for exactly that. Choosing between the two usually comes down to the pressure, temperature and load on the joint.
How do EN1092-1 and ANSI B16.5 slip-on flanges differ?
The two standards differ in how the flange is sized, rated and shaped.
EN1092-1 flanges are sized by DN (nominal diameter) and rated by PN (nominal pressure). The slip-on is the type 01 plate flange, which is flat with no hub. In our range it appears as a name like DN150 EN1092-1 PN16/01B, where 01 is the slip-on type and B is the raised face.
ANSI B16.5 flanges are sized by NPS (nominal pipe size) and rated by class, which we show as 150LB and 300LB. The slip-on has a short hub that the pipe slides into. The drilling is different from EN1092-1, so the two aren’t normally interchangeable.
If you’re not sure which standard you need, check how your existing flanges are sized. DN and PN point to EN1092-1, while NPS and class point to ANSI B16.5.
Which related flanges might you need?
Depending on your pipework, you may also need:
RFSO bored O/D flanges, if your tube is sized by outside diameter, such as hygienic or metric pipework
RFBL blind flanges (raised face blind), to close off a line
Reduced thickness flanges, a flat-faced, lower-cost option for hygienic pipework
All are available in 304 and 316.
What are the common ordering mistakes?
The first is choosing a slip-on where the duty calls for a weld neck. The second is mixing standards, because EN1092-1 and ANSI B16.5 flanges use different drilling. The third is ordering a standard slip-on for tube sized by outside diameter. Tube like this needs a bored O/D flange, which has its bore machined to suit.
What should you tell us when you enquire?
The quickest way to get the right slip-on flange is to start with the size and the standard. Please tell us:
1. The pipe size, or the outside diameter if you’re working with tube.
2. The standard and rating you need, such as EN1092-1 PN16 or ANSI B16.5 150LB.
3. Whether you want a raised-face slip-on flange.
4. The grade, either 304 or 316.
5. How many you need, and what the duty is.
If the pressure or temperature is high, we may suggest a weld neck flange instead, so a short description of the application means we can point you to the right flange first time.
Frequently asked questions
What does RFSO stand for?
RFSO stands for raised face slip-on. The raised face is the gasket seating area, and slip-on means the flange slides over the end of the pipe before it’s welded.
How is a slip-on flange fitted?
The flange slides over the pipe end, is aligned with the matching flange and is then welded on both the inside and the outside. Because the pipe passes into the flange, alignment is easier than with a weld neck.
When should I choose a weld neck flange instead of a slip-on?
Choose a weld neck when the duty is demanding, such as extreme temperature or pressure. Slip-on flanges are cheaper and easier to fit, but they’re best used in low-pressure, low-temperature applications.
Contact Anglo Stainless for more information
For help choosing a slip-on flange, contact us and speak to a member of our team. You can also request our brochure using the form below.
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24″ ANSI B16.5 300LB RFSO A182 F316/L24″ ANSI B16.5 300LB RFSO A182 F304/L24″ ANSI B16.5 150LB RFSO F316/L20″ ANSI B16.5 300LB RFSO A182 F316/L18″ ANSI B16.5 300LB RFSO A182 F316/L
DN450 EN1092-1 PN16/01B RFSO A182 F316/L16″ ANSI B16.5 300LB RFSO A182 F316/LWhat is a slip on (RFSO) flange?
RFSO stands for raised face slip-on. The raised face is the gasket seating area, raised above the bolting face. Slip-on means the flange slides over the end of the pipe and is then welded on both the inside and the outside.
In EN1092-1 this is the type 01 plate flange for welding. In ANSI B16.5 it’s the slip-on form.
How is an RFSO flange fitted?
The flange slides over the pipe end, is aligned with the matching flange, and is then fillet welded on the inside and the outside. Two welds hold it in place, which is why slip-on flanges are described as double welded.
Because the pipe passes into the flange rather than being butt welded to it, alignment is easier than with a weld neck. That ease of fitting is a large part of why they’re so popular.
What are the strengths and limits of slip-on flanges?
Slip-on flanges are cheap, popular and easy to install, which keeps costs down on a project. They’re also thinner than most other flange types.
Slip-on is one of several flange types, and each strikes a different balance between cost, strength and ease of fitting. The trade-off is that slip-ons are best used in low-pressure, low-temperature applications. For demanding duties, a weld neck is the better choice, and our RFWN flanges are built for exactly that. Choosing between the two usually comes down to the pressure, temperature and load on the joint.
How do EN1092-1 and ANSI B16.5 slip-on flanges differ?
The two standards differ in how the flange is sized, rated and shaped.
EN1092-1 flanges are sized by DN (nominal diameter) and rated by PN (nominal pressure). The slip-on is the type 01 plate flange, which is flat with no hub. In our range it appears as a name like DN150 EN1092-1 PN16/01B, where 01 is the slip-on type and B is the raised face.
ANSI B16.5 flanges are sized by NPS (nominal pipe size) and rated by class, which we show as 150LB and 300LB. The slip-on has a short hub that the pipe slides into. The drilling is different from EN1092-1, so the two aren’t normally interchangeable.
If you’re not sure which standard you need, check how your existing flanges are sized. DN and PN point to EN1092-1, while NPS and class point to ANSI B16.5.
Which related flanges might you need?
Depending on your pipework, you may also need:
RFSO bored O/D flanges, if your tube is sized by outside diameter, such as hygienic or metric pipework
RFBL blind flanges (raised face blind), to close off a line
Reduced thickness flanges, a flat-faced, lower-cost option for hygienic pipework
All are available in 304 and 316.
What are the common ordering mistakes?
The first is choosing a slip-on where the duty calls for a weld neck. The second is mixing standards, because EN1092-1 and ANSI B16.5 flanges use different drilling. The third is ordering a standard slip-on for tube sized by outside diameter. Tube like this needs a bored O/D flange, which has its bore machined to suit.
What should you tell us when you enquire?
The quickest way to get the right slip-on flange is to start with the size and the standard. Please tell us:
1. The pipe size, or the outside diameter if you’re working with tube.
2. The standard and rating you need, such as EN1092-1 PN16 or ANSI B16.5 150LB.
3. Whether you want a raised-face slip-on flange.
4. The grade, either 304 or 316.
5. How many you need, and what the duty is.
If the pressure or temperature is high, we may suggest a weld neck flange instead, so a short description of the application means we can point you to the right flange first time.
Frequently asked questions
What does RFSO stand for?
RFSO stands for raised face slip-on. The raised face is the gasket seating area, and slip-on means the flange slides over the end of the pipe before it’s welded.
How is a slip-on flange fitted?
The flange slides over the pipe end, is aligned with the matching flange and is then welded on both the inside and the outside. Because the pipe passes into the flange, alignment is easier than with a weld neck.
When should I choose a weld neck flange instead of a slip-on?
Choose a weld neck when the duty is demanding, such as extreme temperature or pressure. Slip-on flanges are cheaper and easier to fit, but they’re best used in low-pressure, low-temperature applications.
Contact Anglo Stainless for more information
For help choosing a slip-on flange, contact us and speak to a member of our team. You can also request our brochure using the form below.
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