//Bend pipe, canula
    translate([0, -D_CANULA, LENGTH + EXT_D / 2 - REA_WALL + S_CANULA]) rotate([0, -90, 0]) bend_pipe(ed=D_CANULA, id=0, r=D_CANULA, quarter=true);

//ed:      external diameter
//id:      internal diameter
//r:       bend radius
//quarter: if true, yields a 90° turn
//half:    if true, yields a 180° turn

//http://spolearninglab.com/curriculum/lessonPlans/hacking/resources/software/3d/openscad/openscad_helpers.html#

module bend_pipe(ed, id, r, quarter=false, half=false)
{
    difference()
    {

        intersection()
        {
            rotate_extrude(convexity=5) translate([r + id / 2, 0, 0]) circle(r=ed / 2);
            if(quarter)
            {
                translate([0,0,-r]) cube([r*2,r*2,r*2]);
            }
            else if(half)
            {
                translate([0,-r*2,-r]) cube([r*4,r*4,r*2]);
            }
        }
        rotate_extrude(convexity=5) translate([r + id / 2,0,0]) circle(r=id / 2);
    }
}

Traceback (most recent call last):
  File "/usr/lib/freecad/Mod/Draft/Draft.py", line 4190, in execute
    shape = Part.Face(shape)
<class 'Part.OCCError'>: Failed to create face from wire
Traceback (most recent call last):
  File "/usr/lib/freecad/Mod/OpenSCAD/OpenSCADFeatures.py", line 233, in execute
    if fp.Base and fp.Base.Shape.isValid():
<type 'exceptions.RuntimeError'>: check failed, shape may be empty
Exception (Mon May 15 13:34:45 2017): Input shape is null 
Exception (Mon May 15 13:34:45 2017): Input shape is null