When using thicker pipe insulation (1-1/2" or 2" thick), the installer can simply carve out some of the insulation on the inside of the pipe insulation to accommodate the raised union nut.

First you must determine if the OD of your pipe insulation is greater than OD of the union nut. You want to have around a 2" greater OD than the union nut this way you will still have 1" of insulation around the nut on all sides. Find out where the pipe union will fall on your piece of fiberglass pipe insulation. Open up the pipe insulation so you have two C's (halves of pipe insulation) hinged before you. Make two cuts into the insulation on both of the C's. These cuts should represent the width of the union. Pinch the fiberglass and peel out a layer of fiberglass (similar to peeling off a layer of onion). Simply pop the piece of pipe insulation onto the pipe with the carve out falling onto the union nut.

STEP 1:  When you're figuring out how to cut fiberglass insulation, first find out where the pipe union fitting will fall on the piece of fiberglass pipe insulation. Open up the piece of pipe insulation and make a notch with a sharp knife on both sides of the pipe insulation as shown in the next two photos.


Marking Other Side of Pipe Union for Carveout

STEP 2:  Place the piece of fiberglass pipe insulation on a table or on the top of a box (in the field).  Open the pipe insulation all the way so you have two halves of the pipe insulation facing you (two C's).

Two C's of Pipe Insulation (Halves)

STEP 3: Find the notches you marked previously in step 1 and cut slices into the into the pipe insulation.  Make the slices only as deep as necessary, make sure not to cut through the ASJ jacketing.  Make the same cuts on the second halve as well.

Carving Out on Pipe Insulation Halve

Carving Out

STEP 4:  Take your knife and thumb and pinch the amount of fiberglass you want to notch out.  Slowly pull the insulation out

Thumb and Knife Grab Fiberglass Carve

Peeling out Notch of Pipe Insulation

Carve out of both halves

STEP 5: Line the carved out section of the fiberglass pipe insulation onto the pipe union and install as normal.  The notch out for the union will allow the piece of pipe insulation to close fully.  If it will not close fully, redo steps 3 and 4 and take out some more of the insulation.


Carve Out Finished on Pipe Union

If you find that the pipe insulation you are using is not thick enough for the carve out method listed above, look into either stepping up to a thicker insulation for these raised Unions.  You can cut the thicker pipe insulation into a smaller piece and step the insulation up to the thicker insulation and carve out that piece.  You can tape or paint with CP-11 the exposed fiberglass edges on the step up.

You can also use a PVC Union Cover which will save you time and labor on covering pipe unions as well