There are three major categories of fabrication required for industrial usage in the modern world. These categories are metal, plastic, and ceramic. All three of these fabrication methods are being transformed by the emerging technology of 3D printing.
3D printing is, at its base, an enormously simple concept. Although most people think of printing as something done with ink on a piece of paper, that is a limitation of the form that does not have to be observed in any industrial setting. Literally any material that can be rendered into liquid form and extruded through a tube can be used to print. The only variables are the size of the printer and the substrate onto which it prints. 3D printing is notable because the material used contains enough consistency and structural integrity that it can form its own substrate. This allows the creation of solid objects. A 3D printer of metal, for example, can layer a stream of molten metal on top of itself over and over again, building up incredibly complex forms that literally could not be machined or forged by any technology we now have available. The metal in the substrate cools and solidifies, allowing it to be added to, over and over again, until the form is complete. This can be done for metal pieces as small as a single screw. If money were no object and a special printer was built, then it would be possible to print something as large as a battleship. The only limitations are technical.
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Pipes are an excellent example of a metal object that can be printed with a precision and clarity that would simply have been astonishing to previous eras. Few people have even begun to explore the theoretical limits of the combination of limitless metal fabrication and hydraulics, but there is certainly one practical aspect that will be of interest to anyone who works with metal pipes. It is now possible to print the perfect pipe for any situation. It is not only that 3D metal fabrication can match dissimilar sizes, recreate pieces that have been out of production for more than a century, replicate hand-made components, and fit perfectly into any crevasse or tight corridor. Custom fabricators can make a metal pipe of such perfect depth and complexity that one could take a rusty pipe, file all the degraded metal away, take a few pictures of the ragged edges, and then print a repair patch that fit into it with a perfect water-tight seal.