Create a bend tube in OpenSCAD. Work ONLY with openscad >=2016, as the angle parameter in rotate_extrude was introduced there.

bend_tube.scad

// fine mesh
fn = 1000;
// epsilon for clean intersection
eps = 0.1;


module tube(inner=5, outer=10, angle=45, length=250){
    // we want the thing in z direction, thus we rotate on x axis
    

    
    // the real length of the back rotated piece
    rlength = (sin(angle) * (length * 2)) / cos(angle/2);
        
    // the dimension for x can be calculated as well (used for the intersection
    r = (length*2);
    s = 2 * r * sin(angle/2);
    rwidth = r - 0.5*sqrt(4*r*r - s*s);
        
    // ... rlength, rwidth give the bounding box of the tube
    // so when looking at a section of a circle,
    // angle gives the angle of the section and
    // length is in reality half the radius of that circle.
    // the actual tube is then drawn around the central axis.
    //
    // that means, that the resulting tube section will be
    // witht the center at 0,0 and has a height of rlength in z-direction
    echo("Bounding box:");
    echo(x=rwidth, y=outer, z=rlength-(2*offset));
    echo(x=rwidth, y=outer, z=rlength-(2*offset)+10);

    
    offset = sin(angle/2) * outer;
        
        trans = 10;
        
    translate([outer+trans/2,0,5])
    rotate([90, 0, 0]) {
    union(){
        // Because of Rotation:
        //    x   z   y
        echo((cos(angle/2)*outer+outer));
        echo(outer/cos(angle/2));
        translate([-outer-trans, -5, -outer]) 
            cube([2*outer/cos(angle/2)+trans, 5, 2*outer]);
        
        translate([-outer-trans, rlength-(2*offset), -outer]) 
            cube([2*outer/cos(angle/2)+trans, 5, 2*outer]);
        
        
        intersection(){
            translate([-outer-eps, 0, -outer-eps])           
                cube([rwidth+(2*(outer+eps)),rlength-(2*offset),(outer+eps)*2]);
            
            // the tube structure
            // beware: rotation and translation are not communtative
            
            // move down and recenter
            translate([-outer/cos(angle/2)+outer, -offset, 0])
            rotate([0, 0, -angle/2])
            // put into 0,0
            translate([-r, 0, 0])
            rotate_extrude(angle=angle, $fn=fn)
            translate([r, 0, 0])
            difference(){
                circle(r = outer, $fn=fn);
                if (inner > 0){
                    circle(r = inner, $fn=fn);
                }
            };
        }
    }
};
}




tube(8, 11, 45, 250);