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Flanged Ducting

YES! We Have Flanged Duct

US Duct provides duct with flanges (also called angle rings or angle flanges) in black iron, galvanized, or stainless steel (SS) and with or without holes. The duct to which these flanges are attached it available in sizes 3" and up, and also in black iron, galvanized or SS. Construction methods range from laser welded pipe and mechanically lock elbows in lighter gauges to fully welded product in heavy gauge (even up to 1/4")—all depending upon the application.

Types of flanged duct: vanstone flange vs. welded flange

Vanstone flange refers to a technique where by a flange is used to mate 90 degree lips turned onto the pipe or duct component. In this method the flange is placed onto the pipe, the lip turned back and the flange left loose. Typically, the lip is ½” tall (or wide depending on your perspective) when the flanges are pulled together, the VanStoned lips of the pieces that are being connected, are pressed together to make a secure metal to metal connection. Because the flanges are loose on all pieces, alignment of the center-line of the components is easily accomplished. Standard Vanstone pipe lengths are a nominal 59”.

Welded flange refers to flanges that are welded to the duct. The faces of the flanges are the mating surface, as opposed to the Vanstone where the duct lips are mating. Full welded duct flanges have a continuous weld. Intermittently welded duct flanges means that there is a weld at intervals around the duct. Standard welded flange pipe lengths are a nominal 60”.

How to properly align and fit flange duct

When aligning components with welded flanges, positioning against the centerline is important. Because the flanges are welded to the duct and cannot be 'rolled' it is important that the flanges be aligned to the center line of the fittings and will therefore all line up. There are two options for this alignment:

  1. Centerline to the centerline of the holes (align to one hole).
  2. Centerline to the center point between the holes.

Either is acceptable and is a matter of choice (OR MORE IMPORTANTLY) to the existing duct where present.

When field fitting flange duct, and in the case of Vanstone flanges where the flange is left loose, the pipe is typically cut ½” longer than needed and then a ½” lip is hammered back at 90 degrees to the pipe by using the flange as an anvil. This is best accomplished by using deep throat vice-grips to hold the flange squarely on the pipe and far enough back to create the desired lip. In the case of Welded flanges, the pipe is cut to length and then the flange welded in place. (Remember to line up the flange with the centerline.)

Talk to a Duct Guy about the ins and outs of flange duct

Fully welded duct flanges create a leak-free application

The best combination to accomplish a leak-free application with angle rings is to use fully welded duct flanges with the addition of a sealing gasket sandwiched between the angel rings. The sealing gasket is compressed between the flanges by tightening the bolts/nuts. Gaskets can be of a variety of materials, depending on the needs of your application. Some applications can accomplish an acceptable seal using gaskets with Vanstone flanges, however, it is not recommended as shifting of the flanges or gaps between the flange and pipe can contribute to leaks.

For ducting applications that require duct dimensions that are less than 20” in diameter, consider US Duct’s leak free US Tubing option. US Tubing combines the best of flange and gasket connections with the convenience of a clamp together connection system. Contact Us Today To Discuss Flange Ducting. 

Talk to a US Duct expert today about flanged ducting

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