On an isometric drawing, vertical pipes are drawn at what angle from horizontal?

In isometric drawings, vertical pipes are represented at a direct angle from the horizontal plane, which is typically a 90-degree angle. This means that the vertical pipes are shown as truly vertical lines, while the horizontal pipes are drawn at 30 degrees from the horizontal axis.

The use of a 90-degree angle for vertical pipes helps maintain clarity in the representation of the three-dimensional layout on a two-dimensional surface, ensuring that the vertical orientation is easily distinguishable from horizontal or sloped pipes. This clear representation is crucial in isometric drawings, which aim to visually convey the spatial relationships and dimensions of piping systems and components accurately.

In summary, the choice indicating 90 degrees for vertical pipes aligns with standard practices in creating isometric illustrations, making it the correct answer.