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NOMINAL THICKNESS FOR STANDARD PRESSURE CLASSES OF DUCTILE-IRON PIPE
Size In. Outside Diameter In. Pressure Class 1
150 200 250 300 350
Nominal Thickness - In.
3 3.96 - - - - 0.25 2
4 4.80 - - - - 0.25 2
6 6.90 - - - - 0.25 2
8 9.05 - - - - 0.25 2
10 11.10 - - - - 0.26
12 13.20 - - - - 0.28
14 15.30 - - 0.28 0.30 0.31
16 17.40 - - 0.30 0.32 0.34
18 19.50 - - 0.31 0.34 0.36
20 21.60 - - 0.33 0.36 0.38
24 25.80 - 0.33 0.37 0.40 0.43
30 32.00 0.34 0.38 0.42 0.45 0.49
36 38.30 0.38 0.42 0.47 0.51 0.56

1 - Pressure Classes are defined as the rated water pressure of the pipe in psi. The thicknesses shown are adequate for the rated water working pressure plus a surge allowance of 100 psi. Calculations are based on a minimum yield strength of 42,000 and a 2.0 safety factor times the sum of the working pressure and 100 psi surge allowance.
2 - Calculated thickness for these sizes and pressure ratings are less than those shown above Presently these are the lowest nominal thicknesses available in these sizes.

NOTE: Per ANSI/ AWWA C140/A21.50 the thicknesses above include the 0.08" service allowance and the casting tolerance listed below by size ranges:

SIZE (Inches) CASTING TOLERANCES (Inches)
3 - 8 -0.05
10 - 12 -0.06
14 - 36 -0.07