Tank Shell in Courses: flat pattern

The shell of a storage tank or silo in courses and plates from stock, the vertical seams staggered, with a nozzle or manway marked on its plate. The shell of a storage tank or silo too big for one plate: divided into courses the width of the stock plate and each course into equal plates, the vertical seams of alternate courses offset by half a plate, with a nozzle or manway marked on the plate it falls on.

Configurations

• Plain shell. Courses and plates only.
• With a nozzle or manway. One radial opening, marked on the plate it falls on, kept clear of every seam.

A worked example

The plain shell configuration with the sizes SheetMorph opens with, in mm. 12 plates: 4 courses of 3: 12 parts, 15 seams.

How it is developed

Development of rolled plates (unrolled cylinder). This is an exact development: the surface unfolds without stretching, so the pattern closes exactly.

• Each plate unrolls to a rectangle 6289.4685 long round the shell and as high as its course. The plates of a course are alike; the top course is narrower, cut from the same stock.
• The vertical seams of alternate courses are offset by half a plate, so that every vertical seam meets the middle of a plate above and below it.
• Roll each plate to the shell with its long side round it.

Checked before it can be exported

Every pattern SheetMorph draws is checked against the 3D part it comes from. For this example:

• Surface connectivity (passed): 1056 facets form a shell of 4 courses of 3 plates, open at its foot and top: every edge inside a part joins exactly two facets, every open edge one (V - E + F = 0).
• Developed edges equal true 3D lengths (passed): 3168 facet edges compared between the 3D surface and the flat pattern (max deviation 1.54e-11).
• Shared edges and seam closure (passed): 1044 internal edges are shared vertex-for-vertex between adjacent facets; 0 seam(s) have mating edges of equal true length (max deviation 0).
• Developed facets consistently oriented (passed): All developed facets are counter-clockwise (outside face up); none is mirrored or degenerate.
• Developed area equals surface area (passed): Facet area in 3D and in the flat pattern agree (difference 5.66e-7).
• Cut outlines closed and non-overlapping (passed): 12 closed outline(s); no outline crosses itself or another outline.

Assumptions

• The pattern is developed on the mid-thickness surface; inside or outside sizes are converted to it by the thickness.
• Curves are chains of chords between division points.
• No seam, lap, weld-preparation or pressing allowance is added.

Limits of this module

• Every course has the same thickness and the same inside diameter; a shell stepped in thickness is made course by course.
• One radial nozzle at most; nozzles off the radial, and the reinforcing pad round one (see Reinforcing Pad), are not drawn here.
• Seams are offset by half a plate on alternate courses; another offset, and the clearances a design code asks between seams and openings, are for the designer to check.
• The bottom, the roof, the wind girder and the top angle are not modelled.
• Curves are chains of straight chords between division points.
• No seam, lap, weld-preparation or pressing allowance is added, and plates are not nested onto stock sheets.

Conventions

Coordinate system. The part stands on the Z axis with End A at Z = 0. Angles round the axis are measured from +X toward +Y, counter-clockwise seen from +Z.

Divisions and thickness. A circle is divided into 4N equal chords. Sizes are inside, mid-thickness or outside sizes; the pattern is developed on the mid-thickness surface and the views show the sizes as entered.

Courses. The shell stands on the Z axis, its foot at Z = 0. Courses are counted from the foot. Each is as high as the plate is wide, and the top course takes what is left of the height; give a plate width that suits the stock.

Plates. Each course is divided into the fewest equal plates no longer than the stock plate allows, round the mid-thickness girth. Seam 1 of the odd courses is on +X; the seams of the even courses are turned by half a plate, so that no vertical seam lines up with the one above or below it.

Nozzle. The nozzle is radial: its axis crosses the tank axis at the height given, at the angle given round from +X. Its hole is marked on the plate it falls on, taken round the shell, so it is wider laid flat than across. It must keep clear of the seams round it by twice the plate thickness at least.

One thickness. Every course is the one thickness given. Where the courses are of different thicknesses, as on a tank sized for the head of its liquid, make each course in turn with its own thickness and the same diameter.

Change the sizes to your own in SheetMorph, check the drawing, add seam and flange allowances, and export DXF, PDF, SVG, CSV or G-code. Check every pattern against your own standards before cutting.

Other vessels

• Shell with Nozzles: A cylindrical shell unrolled to a rectangle, with the holes for up to four radial nozzles marked in their developed shape.
• Silo: A silo, bin or hopper as one job: the body, the cone bottom from its wall angle, the spout, a support skirt and a cone roof, with what it holds.
• Reinforcing Pad: The pad welded round a nozzle on a shell or a pipe: rolled to the shell, with the hole for the nozzle and a tell-tale hole, whole or in two halves.
• Sphere: A sphere made of plates: gores from pole to pole, or zones round it, with a round cap at each pole.
• Dished Head: A vessel head in petals round a crown plate: torispherical, hemispherical, semi-elliptical (2:1), or a cone with a knuckle.