Slip-on flanges, also known as hubbed flanges, have a hub with a very low profile. This type of flange is usually connected to a pipe by one or two fillet welds (one outside the flange and one inside the flange), it is however possible to use only a single weld. Slip-on flanges are produced in many sizes and favoured for lower pressure applications (ASME class 600).
Slip-on Flange Cross Section
A slip-on flanges 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.
However, if a welding neck flange cannot be used due to space limitations, a slip-on flange may be a suitable alternative.
Slip-on Flange
Advantages of slip-on flanges relate to lower procurement costs, less required skill for making the weld, lower accuracy requirement for pipe cutting, and no weld preparation requirements for a pipe end weld.
Limitations for slip-on flanges relate to:
Although cheaper than a welding neck flange, there is little price difference if two welds are performed and both must be checked using non-destructive testing techniques.
Non-Destructive Testing (NDT) Techniques
There are no specific NDT techniques used in conjunction with slip-on flanges. If the slip-on flange is fillet welded, then a dye penetrant test may be performed on the weld. A visual inspection of the mating faces and pipe is possible.
ASME Standards
The standards ASME B16.5 and ASME B31.3 specify the requirements for slip-on flange installation, maintenance, and testing.
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Slip-on flange is a popular type of pipe flange designed to accept pipe into the bore/center of the flange for welding around both the Outer Diameter (OD) of the pipe and on the interior side of the connection. You may recognize them:
The slip-on flange is a simple and excellent alternative to a weld neck as it does not have a weld bevel, and therefore allows the pipe to be adjusted in length relative to its position of the flange.
The bore of the slip on will give ample amount of space for the matching pipe. This allows for enough working space for the welder and fabricator to make the connection.
This flange type is extremely common in lower pressure applications. Most slip on style flanges will have a hub which will often appear similar dimensionally to a raised face. It can be furnished without a hub if space is limited and the application allows for a ring style slip on.
Slip ons in higher pressure classes are often made with the height of a lap joint for a better connection. If the hub height is not a concern and a lap joint is not readily available, customers will sometimes opt for a slip on made to a lap joint style with a machined hub.
This is because a slip on style flange will accept a pipe with a fillet weld connection, whereas a weld neck flange will have a reinforced hub at the base and form a weld bevel connection directly to the butt weld end of a pipe. This tapered hub allows for stronger service in a mechanical stress environment.
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