The palette
Five colors: a main tone, two highlights, one shade, and a dark blue for the background. This project is simple enough to skip the line art: I build the shapes straight from the shades.
A pipe is a cylinder
Remember the cylinder from the shading lesson? A pipe is the same shape, lying down or standing up. With the light from the top left, the vertical pipe goes near white, then the main tone, then the shade, and a light gray on the far right edge as a small rim light. The horizontal pipe goes the other way round: light on top, dark at the bottom. And because the vertical pipe is in front, it casts a shadow on the horizontal one.
Angle, junction, sleeve
- Angle. The pipe colors bend around a corner. The inner corner gets a slightly darker tone, because not much light reaches it. One dark pixel inside and a couple of light ones on the outer curve smooth the bend.
- Junction. A 9 by 9 square with cut corners. Highlights on the top and left and a darker edge give the feel of a bevel. Four bolts, each one pixel with a darker surround. Above it, a thread: the pipe colors shifted one pixel left and right.
- Sleeve. A 4 by 7 band, shaded like the pipe, with a pixel of shadow on each side. Cut the pipe pixels at its edges, so the pipe looks like it goes through.
Build your own layout
The point of these four parts is that you never draw a pipe network from scratch again. Copy, paste, flip, and combine. Use them as a background or a foreground in a platformer. Then try your own route: two angles, one junction, a sleeve in a long run. The shading rules stay the same wherever the pipe goes.