TECHMAIL: Insert Flanges

What is an Insert Flange?
By Millard Fitzgerald, Jr.
Reprinted from Flow Control magazine, May 1997 ©1997 Witter Publishing Corporation

Insert Flanges have been used on piping and pressure vessels for almost a half-century and offer many advantages. They have a proven track record in the food, chemical, petrochemical and pharmaceutical industries. Various styles, materials and pressure ratings are available to satisfy the varied requirements of the end user and his piping contractor.

What is an Insert Flange?

Insert Flanges are a specialty in the arena of pipe size flanges and consist of two parts - the insert and the flange ring. The flange ring is the outer part of the insert flange assembly, containing the bolt holes. Except perhaps for the thickness, it is similar to the standard B16.5 flange beyond the raised face or gasket surface. It's function, along with the bolting, has but one major purpose, and that is to be the clamp that applies the necessary axial force against the insert to seat the gasket and to withstand the pressure and other piping forces and moments. Material selection is relatively simple, considering only atmospheric corrosion, strength, temperature and economy.

The insert, on the other hand, has several duties to perform and for that reason is offered in many different styles. In some ways it is similar to a pipe lap joint stub end. The front portion of the insert contains the gasket-seating surface, which must be machined true and with the proper finish to seat and seal against a variety of different gasket materials and styles. The rear portion contains a suitable surface or hub for the attachment fillet or butt welds to the process and jacket pipes. Depending upon the style, the OD (or shoulder) at the rear may be may be sized to accept the bore of the jacket pipe. Again, depending on the style, this shoulder may even contain a step to simulate a buttweld with integral backing. The machined bore is sized to allow the process pipe to slide inside as a slip-on or socket, or to match the ID of the pipe when provided with a butt welding hub or even threaded to accept the threaded end of the pipe. The materials from which the insert is made must be compatible with both process fluids and jacket fluids and provide a reasonable level of corrosion resistance.

Since insert flanges are a specialty item, they are manufactured in much smaller lot sizes than the B16.5 flanges. And because they are not a commodity item like their B16.5 flange relatives, they are manufactured to closer tolerances. They also offer an economical means of fabricating piping spools.

Insert styles are offered as butt weld, slip-on, socket, thread-on and even blind. They can be obtained with the same gasket finishes and facings as B16.5 flanges, including male and female, tongue and groove, and even grooves for O-ring and RTJ gaskets. Some manufacturer offer custom styles to meet almost any requirement. Polished surfaces are also available when required by the process conditions.

The ability of the flange ring to rotate is a feature appreciated by piping installers and maintenance personnel for maintaining bolt hole alignment since field conditions are far less precise than the fabrication shop. The two piece construction of the insert flange also offers the economy of matching the insert material to the process pipe (usually some corrosion resistant alloy) while the outer flange ring may be manufactured from steel. When the environment requires the flange ring to be made of some alloy the rotating feature is still maintained. The insert and flanges can be made of just about any alloy used in process piping.

Development of Insert Flanges

Insert flanges were initially developed in the 1950s as a way of fabricating pipe without welding, using roller expansion technology. Roller expansion, even without a seal weld, was and is a proven and highly reliable method. When performed properly the roller expansion method, similar to sealing tubes into a tubesheet of a shell and a tube heat exchanger, provides a strong mechanical lock and offers an alternative where welding is not permitted.

Insert flanges then incorporated the idea of the rotating flange ring. This contribution has saved time and money in the fabrication of the piping systems, by making the alignment of insert flanges for bolting especially easy.

As the insert flange was being improved upon and changed to meet new applications, an insert flange designed for jacketed or containment pipe cations became an industry standard. Engineers began specifying this insert flange because it was designed specifically for jacketed piping. Fabrication of jacketed pipe spools was made easier and more efficient.

Insert Flanges and Jacketed Piping

The use of insert flanges, made specifically to make jacketed piping assembly easier, also avoids the cost of alternate jacket closure methods such as closure rings, swaging the ends of the jacket pipe and custom machining the backs of standard B16.5 flanges. Instead the inserts are machined to offer easy and proven attachment methods to the process pipe and jacket pipe via slip-on type fillet welds, butt welds, or full penetration corner joints.

[...]

[Fabrication]

[Reducing Temperature Changes in Jacketed Piping Systems]

[Engineering Considerations]

For the remainder of this article and much more information about insert flanges, see < http://www.insertflanges.com/what.shtml >

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Frequently Asked Questions
< http://www.insertflanges.com/faqs.shtml > Received on Thu Oct 26 12:45:00 2000