Creating the profile

Choose the Line option, located in Geometry->Create->Straight line.
Enter the following new points in the command line: (0, 11), (8, 11), (8, 31), (11, 31), (11, 11) and (15, 11). Press ESC twice to indicate that the process of creating lines is finished.

Profile of one of the disks around the pipe

From the Copy window, choose Lines and Translation. A translation defined by points A (0, 11) as first point and B (15, 11) as second point will be made. In the Multiple copies option, enter 8 (the number of copies to be added to the original). Be sure than the 'Collapse' option is set, and then Select the lines that have just been drawn and press ESC.

The profile of the disks using Multiple copies

Create a line using Geometry->Create->Straight line. Use the contextual option Join or press <Ctrl-a> and select the last point on the profile (at the right part of the profile). Now choose the option No join Ctrl-a and enter new point (160, 11) in the command line. Press ESC twice to finish the process of creating lines.
Again, choose the Line option and enter the new points (0, 9) and (160, 9). Press ESC twice to conclude the process of creating lines.