Collar Studs

On a shell-and-tube heat exchanger with a removable tube bundle, the stationary tubesheet is clamped between the shell flange and the channel or bonnet flange. Ordinary studs pass through all three, so taking off the channel for tube inspection or cleaning also loosens the shell-side joint.

A collar stud has a collar part way along its length. The collar sits in a counterbore in the tubesheet and holds the tubesheet and shell-side gasket against the shell flange. When the channel nuts come off, the collar studs keep the shell-side joint together, so the channel or bonnet can be removed without disturbing the shell-side gasket or pulling the bundle to replace it.

Collar studs only hold the gasket in place while the channel is off. They do not replace the full set of bolting, and every stud and nut is installed and tightened before the exchanger goes back into service.

TEMA RCB-11.8 covers collar studs for removable bundles. When the purchaser specifies them:

• Every fourth stud in the bolt circle is a collar stud, with a minimum of four.
• Collar studs are Type I (solid) or Type II (nut type).
• The tubesheet holes are counterbored to accept the collars.
• Collar studs are not sufficient for a shell-side pressure test. All pressure bolting is installed and tightened before pressurizing.

As an alternative, TEMA allows those tubesheet holes to be drilled and tapped, with the studs double-nutted or given machined flats.

API 660 calls for collar studs or tapped holes on at least 25% of the bolts, with a minimum of four, and for their locations to be shown on the drawings and marked on the tubesheet. Some owner specifications go further and require one-piece integral collar studs. Check your exchanger data sheet and specification for the style and number required.

Both types do the same job. The difference is how the collar is made and held in place.

Integral collar studs are turned from bar large enough for the collar, with the threads cut or rolled on each side. There are no loose parts, and the collar cannot move.

Nut-type collar studs use a separate collar tapped to the stud thread. The collar is run to its location and locked so it cannot turn. This style lets the collar position be set to suit the joint.

Collar studs are usually made in the same grade as the rest of the exchanger bolting. Common grades include A193 B7, B7M for sour service, B16 for higher temperatures, A320 L7 for low temperatures, B5, and nickel alloys such as Inconel 625 and Inconel 718.

For nut-type studs, the collar is made from the same material as the stud unless your specification says otherwise. Tell us the grade, coating and marking your specification calls for. Compare grades in our Fastener Materials Matrix.

To quote collar studs, tell us:

• Thread size and series, for example 1-8UN-2A, and overall length.
• Collar type: integral (Type I) or threaded to the center (Type II).
• Collar size: round diameter or hex across flats, thickness, and location from the end (or centered).
• Ends: square, flats or plain.
• Locking for threaded collars: set screw size, tack weld or none.
• Material, coating, marking and quantity, plus any matching heavy hex nuts.

If you have a drawing, upload it and we will make the studs to it. You can also build one in our fastener drawing generator by choosing the collar stud type, then download the PDF or send it straight to our team.