Eh, there's really nothing to it. I assume you actually mean the metal pipes.
Blender can automate some stuff pretty easily. I don't recall the exact set of steps I took, but if I were to do it again, I'd do this:
First, you need to set the grid to 3 lines, scale of 0.50, and 8 subdivisions. This'll make one Blender unit - that is, the size of the major/thick grid spacing when you zoom out to see the whole scene - equal to one half of a 1m node in Minetest, and one subdivision will correspond to one pixel, assuming a 16px texture. The grid center/origin will correspond to the dead center of the node, and the first major grid lines away from the origin will be the node's sides. Make sure you draw everything at the proper size. Here's the straight pipe displayed with those grid settings when the view is not aligned to any side:
All of this needs to be done while looking at the node from one of its sides - your view must be snapped to one side with keypad "1", "3", or "7" (perhaps with "Ctrl"). Otherwise, things will go in weird directions when you try to move stuff around. I believe I drew the curved pipe while looking at it from above (keypad "7"). You can pan and rotate your view however you like as you work, so long as you always snap the view to one side before altering the model. Note that the pixel-sized subdivisions will not be visible when the view is not snapped, and when it is, you'll get far more grid lines than you asked for (I'm not sure how to limit this).
* Snap the cursor to the grid center.
* Create a circle with at least a few dozen sides (this really needs to be an even multiple of the resolution of the texture you'll be using, e.g. 32 sides for a 16px texture). Fill it, and rotate it if necessary to face the side of the node where you want the pipe to start. The diameter of this circle will be the diameter of the pipe (obviously).
* Move the circle to the side of the node you chose for the start of the pipe.
* Move the cursor to one corner of the volume, but inset it a little bit from the corner, *exactly* evenly in both directions, say 3 subdivisions (e.g. 3 pixels' worth).
* Set the pivot point to the cursor.
* Select the circle and extrude along one axis, toward the center of the node. Just a small, random distance, you'll set the exact final position in a moment.
* The now-extruded face should now be selected. Scale it, locking the scaling mode to just the axis you extruded along. Since a single face has no thickness, and the pivot is set to the cursor, and scaling uses this pivot, this action will just move the face, but in a special way.
* While scaling, press "0", Enter. This will cause the face to snap to a position even with the cursor, along just the axis you were scaling on. It'll remain offset from it - leave it there.
* Execute the "Spin" tool in the Toolbox sidebar on the selected face. 90° angle (or negative 90°, if needed), at least a dozen steps. Blender will repeatedly extrude, rotating a little bit each time, until it hits 90°. The cursor will form the center of rotation, and hence the center of the pipe's bend.
* Select the face at the other end of the bend (that is, the last one Blender just drew), and extrude it along its new direction, i.e. orthogonal to where you started, stopping at the corresponding side of the node.
* Select all, re-calculate normals (ctrl-N) to turn everything right-side-out, and set the shading mode (also in the Toolbox sidebar) to "smooth". Select the two ends, set those to "flat". This affects how light and shadow play across the surface, and is part of what makes the the pipes look smooth.
At this point I would copy and paste one of the flanges from the straight pipe, and place it appropriately. After that, texturing/UV-mapping the assembly. Once that's done, I'd copy and paste the new, now UV-mapped flange, and move the copy to the other end of the pipe (by copying this one now, the copy will also be properly UV-mapped, saving some time)