Cylinder with Branch Hole flat pattern

What it is

The shell course with the branch hole already in it. It is the missing half of every branch job: the branch part gives the pattern for the branch, this one gives the pattern for the pipe it enters. It is also the only sheet in this catalogue with an internal cut-out — the outline comes out with two loops, the rectangle of the course and the hole.

Where it is used

Headers and manifolds with take-offs, vessel shells with nozzles, piping with welded branches, any shell that is going to receive a branch.

Measurements the calculation needs

• D2 Outside diameter of the shell
• H Length of the shell
• D Diameter of the hole
• ANG Angle of the branch to the shell axis
• DV Divisions
• THK Plate thickness

Calculate with your own measurements

No account needed: enter the measurements in millimetres or inches and get the figures and the drawing. The scaled PDF template, the DXF for the cutting table and the 3D model take a free account.

Diameters and sides are outside measurements. The flat pattern already allows for the plate thickness, working on the mean line.

Units: mm inches

Outside diameter of the shell D2 (in)

Length of the shell H (in)

Diameter of the hole D (in)

Angle of the branch to the shell axis ANG (°)

Divisions DV

Plate thickness THK (in)

Calculate free

Worked example

The values the form comes pre-filled with, run through the tool itself:

Outside diameter of the shell	15-3/4" (15.748)
Length of the shell	23-5/8" (23.622)
Diameter of the hole	7-7/8" (7.874)
Angle of the branch to the shell axis	90°
Divisions	32
Plate thickness	1/4" (0.2362)
The flat pattern fits a plate of	48-3/4" × 23-5/8"

Result of the example

Plate	48-3/4" × 23-5/8"
Area and weight	7.7 ft² · ≈ 73.8 lb in 1/4" steel

Guides about this part

• Pipe saddle calculator and development: how to lay out a pipe-to-pipe branch (tee) at 90 and 45 degrees

Frequently asked questions

Which diameter do I enter, the branch or the hole?

The HOLE, and the difference matters: for a branch set on top of the shell the hole goes at the branch's bore, so the branch wall has a seat; for a branch set into the hole, at its outside diameter. The welder decides, and the number entered is the decision — that way the calculation need not assume the branch's wall thickness, which may not match the shell's.

Why does the hole come out wider than the diameter I entered?

Because the sheet is flat and the pipe is round. Unrolling the shell stretches everything off the mid-line. A 200 hole in a 400 shell in 6 mm plate comes out 206.3 wide on the sheet — a little over 3% more.

And the hole's length along the pipe?

It is the diameter divided by the sine of the angle, exactly. At 90 degrees that is the diameter itself; at 45, forty-one percent more. Not a guess: the algebra closes in two lines.

Where does the shell seam go?

Diametrically opposite the hole, which is where it goes on the part — a longitudinal weld does not run through a cut-out.