My Mechanical Engineering Handbook gives the I.D. of standard weight 28" steel pipe as 27.250" (wall thickness = 0.375"), but doesn't show this as Schedule 40. There is no Schedule 40 listed for 28" dia.
My Machinery Handbook shows for:
24" 22.624"ID .688"wall
32" 30.624"ID .688"wall
Properties of American National Standard Schedule 40 Welded and Seamless Wrought Steel Pipe
hth