There are many ways to build industrial pipe shelves. In this post, I'll cover some of the design thinking I did for a recent project.
Black Pipe or Galvanized Pipe
Whether you go with black iron pipe or galvanized pipe (similar in price), the look can be varied by simply choosing different connectors. Here are three options shown from the side (parallel with wall). The wooden shelf boards are shown with diagonal hash marks.
Connectors Add Mass
Add visual mass with connectors where the narrow vertical pipes meet the shelf boards. It just looks better this way. Think ancient Greek columns. You don't want straight pipe passing through the shelf - it looks weak. You need a transition. At a minimum, put a connector beneath each shelf (as shown in Option #1 front-edge leg)
Design Option #1 is most labor-intensive option. Careful hole drilling and fitting of the pipe required - this is not trivial. Drill holes to pass the OD of the pipe by 1/6" - 1/8". This means 1-1/8" diameter hole for 3/4" pipe. The caps and close nipples are optional; the shelf can rest on the top edge of the T and the 90 (or in ~1/2" deep stopped round mortises). Use a drill press for all holes.
Design Option #2 utilizes flanges and requires far less labor to assemble. No holes need to be drilled through the shelf boards. You trade a little shelf space for ease of assembly. A simple, substantial, symmetric look. Pan head screws work well to attached flanges, just remember to hit their heads with a black Sharpie if you use black iron pipe.
Design Option #3 sandwiches a short nipple in through holes (close or 1-1/2" depending on wood thickness) between two couplers. Labor similar to Option #1. There are a couple variations on the way the back posts are configured (closest to the wall). Use a drill press.
Design Option #4 is basically a scaffold of pipe with boards laid across it. Most of the frame is entirely outboard of the shelf edge. Easy to build. No holes needed. Might benefit from addition of a few conduit clamps to anchor boards to pipe.
Varying the Pipe Diameter
For a single bank of shelves like this, you might consider using 1" pipe for the outer two post assemblies and 3/4" for the intermediate ones. Also, using the principles of graduated shelf spacing (i.e., Shaker furniture) can help improve the design. A good rule of thumb for determining vertical distance between shelves is 10", 12", 16", and 18". If you plan to shove rubbermaid totes underneath the bottom shelf, measure the height of those first and add about an inch. You might also consider their width for optimal horizontal spacing. Otherwise, horizontal spacing between posts should be even (measure from centerlines of pipe).
A good example of flange-heavy Option #2.
A variation of Option #1. Note that the shelf holds small items (not tons of heavy books) and is anchored to the wall at either end by flanges.
An example of Option #1 with integrated lighting and wall mount (no posts to floor or ceiling). Make sure you hit the studs, use long screws, or consider adding horizontal ledgers to the walls before you start. Size them 1" wider than the flanges, chamfer their edges, paint them to match the wall color, and attach the flanges to those rather than to the sheetrock/studs. This is about as much weight as I would be comfortable with given this wall-mount configuration.
Another example of Option #1.
Example of Option #4. You don't always need to screw the unit to the floor. In this case, I might just apply stick-on felt pads, cut to match the flange diameter, to the feet. See how tippy your loaded-up shelf is first, then decide whether to anchor it or not.
Anchor Down, Skipper
No matter how you build it, supporting the wight of books should a consideration. The sketches below show a few ways to attach a shelf to something stable.
A quick sketch helps the client visualize the room and shelving configuration. It also forces you (the builder) to think about all the little connections and fit issues before getting to the site. Its easier to count up the needed parts and determine where custom-length pipe is needed. This particular sketch will lead to design improvements (and another sketch). Industrial pipe shelves look super simple, but once you start customizing, things can become finicky. A good idea for your first go round is to a.) design a single unit that stands alone (does not wrap around corners or tie into other shelves), b.) vary the vertical shelf spacing, and c.) call it good.