YUDIbt

If you going to model any industrial type 3D model with pipe works, you will surely need to have several pipe fittings including bens and T’s. In most if these industrial pipe-works the fittings are connected through flanges using nuts and bolts. Therefore, for this tutorial I have selected to model a high-quality 90° bend with 2 flanges on its both ends. Once you have gone through the tutorial, you will be able to model similar flanges with different angles and pipe sizes. If you want, you can use this method to model low-poly flanges as well.
The flange section I am going to model consists of 2 flanges and a pipe bend section. Since this tutorial going to be bit longer, I have divided it into 2 tutorials. The first tutorial named as “Model high quality pipe flange in 3D Max” and it covers the flange modelling part. This is the second tutorial, and this will teach you how to model the bend section and how to connect with the flange section. To obtain the best results, I am strongly recommended to go through my first tutorial.
Open the 3D max file which is having the flange you have modelled in the first part of the tutorial. You should have something like below in your viewport.

Select the flange object and disable (turn off) the TurboSmooth modifier to obtain the low poly object.

Right click on the “Select and Move” Toggle to obtain the “Move Transform Type-in” and set all X, Y, Z values under “Absolute:World” to zero to bring the flange object to origin (0, 0, 0).

Go to Polygon Sub-object level of the object and select the top most polygon ring of the flange (see figure below).

Push the “Grow” button under the “Selection” rollout to grow the selected polygons up to chamfered polygons. Then delete the selected polygons and exit from Polygon Sub-object level.

Go to top viewport, turn on Snap and click the Tube button (Create > Geometry > Standard Primitives > Object Type rollout > Tube) to draw a Tube object. Before draw the Tube object, change the number of “Sides” under the “Parameters” rollout to the number of sides you are having for the flange (for me, it is 16 sides). (Note – If you followed me correctly in the previous tutorial, the number of sides will be twice as the number of holes you are having in the flange.)
You have to make sure that the two radiuses of the created Tube exactly match to the hole of the flange we made by deleting some polygons. Don’t worry about the height of the Tube, we can correct it later.  You will not get the correct result at once because it is bit difficult to draw a Tube than the Cylinder. Use the top viewport, it will make the job little easier.
This is the tube I have created on the flange with correct radiuses; hope you will also get a similar result.

Correct the height of the Tube as you like by changing the “Height” under “Parameters” rollout. You don’t need to concern about the height too much, you can correct it later. If the Tube gone through the flange, move it along the Z-axis until it comes out of the flange. Increase the Height Segments of the Tube to 6 or any even number nearby. Don’t increase it too much 6 or 8 will be enough.

Select the Tube object and apply Bend modifier to it using the “Modifier list”. Increase the Angle under “Parameters” rollout to 90.0. Hope you got a nice pipe bend, if not change the “Bend Axis” and check. You should get the correct result from one of them.

This is what I got as the result.

Now you can see the basic shape of the pipe bend you are going to have. If you are not interested in what you got, go back to Tube parameters and change the Height of the Tube until you get the correct shape.

Once you satisfy with the shape of the bend, right-click on the tube and convert it to an Editable Poly. Go to Polygon Sub-object level of the object and select and delete exactly a half of the object (see figure below).

Now, exit from the Polygon Sub-object level and move the remaining part of the bend along the Z axis to some distance using “Select and Move” toggle.

Go to Perspective viewport and rotate the viewport (not the object) to an angel where you can clearly see the flat bottom of the bend section. Go back to Polygon Sub-object level and then select and delete all the polygons in that flat bottom (see figure below).

Then again exit from the Sub-object level and perfectly place the “bend” section on the opening of the “Flange” using “Snap” tool and “Select and Move” toggle. If you followed the steps correctly, the internal and external faces of the bend should correctly match with the faces of the flange. This is what I got.

Select the flange and attach the bend to it using the “Attach” option (button) available under “Edit Geometry” rollout. Go to Vertex Sub-object level, select all the vertices and weld them together without losing the vertices nearby (use “Weld” button under “Edit Vertices” rollout).

Now, go to Front or Left viewport where you can see the finished bend part as below.

Select and Mirror the object along any direction to obtain another bend part.

Rotate the second bend part from a 90° (use Snap tool) to make the cut planes parallel.

Place one part on the other using “Snap” and “Select and Move” toggle tools to make the complete 90° bend section.

Attach the two sections together as you done previously using the “Attach” option (button) available under “Edit Geometry” rollout. Go to Vertex Sub-object level, select all the vertices and weld them together without losing the vertices nearby using “Weld” button under “Edit Vertices” rollout. Turn on TurboSmooth modifier and see how the final result looks like.

You can use this method to model different shapes of flange bends by changing last few steps. Here are few example bends.