Gravity Flow Service

Due to its high strength and stiffness with the resulting ability to support heavy earth and other type external loads, ductile iron pipe has found wide acceptance in gravity flow service such as sewer lines, outfalls and culvert pipe.

The problems of infiltration, root intrusion, and leakage are eliminated in sewer service with the use of the Fastite joint. The resistance of ductile iron to impact, the convenient pipe lengths, and the ease of assembly represent additional advantages of using ductile iron pipe in sewer service. In addition, ductile iron pipe has an inside diameter greater than nominal pipe size, which results in greater flow capacity with potential cost savings. Ductile iron pipe is available for normal domestic sewage service with cement lining. Other linings are available for sewer and special services. See Linings.

Ductile Iron Culvert Pipe

ASTM A716 is the standard for ductile iron culvert pipe covering sizes 14" through 64" manufactured per ANSI/AWWA C151/A21.51. AMERICAN ductile iron culvert pipe is furnished with Fastite or other suitable joints and is coated inside and outside with an asphaltic coating approximately 1 mil thick; or may be cement lined.

Minimum pressure classes are shown in this standard for sizes 14" through 64" for the range of cover from 2 to 41 feet, depending on size, based on Type 5 trench condition. This is the same Type 5 laying condition shown in current AWWA Standards C150 and C151. See Fig. 3-2. Pipe thickness for other conditions can be calculated by using formulas and design criteria in AWWA C150, except with modifications as specified in A716.

Ductile Iron Gravity Sewer Pipe

ASTM A746 is the standard for ductile iron gravity sewer pipe in sizes 4" through 64" with Fastite joints.

The design of AMERICAN ductile iron gravity sewer pipe in this standard is based on the same formulas and design criteria as pipe designed per ANSI/AWWA C150/A21.50, except that pipe with a flexible lining is designed with maximum allowable deflection of 5% of the outside diameter of the pipe instead of 3%. In the A746 Standard are thickness tables for cement-lined pipe and for flexible-lined pipe.

The thicknesses for cement-lined pipe will be the same as those in AWWA C151 for the same depths of cover and laying conditions. See Maximum Depths of Cover. The table below shows depths of cover for the different laying conditions for 4" through 64" pressure classes of flexible-lined pipe. The shaded areas indicate the depths of cover which are different from cement-lined pipe per A746 and from AWWA C151 as shown in Maximum Depths of Cover. These depths of cover are controlled by design deflection (instead of ring bending stress) and are greater than those for cement-lined pipe due to the 5% design deflection.

Gravity Sewer Pipe ASTM A746 Pipe with Flexible Linings
Depths of Cover for Standard Pressure Classes

Size
(in.)
Pressure
Class
Thickness
(in.)
Laying Conditions
Maximum Depth of Cover in Feet
Type 1 Type 2 Type 3 Type 4 Type 5
4 350 0.25 53 61 69 85 109
6 350 0.25 26 31 37 47 65
8 350 0.25 16 20 25 34 50
10 350 0.26 111 15 19 28 45
12 350 0.28 101 15 19 28 44
14 250 0.28 - 111 15 23 412
14 300 0.30 - 13 17 26 432
14 350 0.31 - 14 19 27 44
16 250 0.30 - 111 15 24 412
16 300 0.32 - 13 17 26 432
16 350 0.34 - 15 20 28 452
18 250 0.31 - 101 14 232 402
18 300 0.34 - 13 17 26 432
18 350 0.36 - 15 19 28 452
20 250 0.33 - 101 14 232 402
20 300 0.36 - 13 17 26 432
20 350 0.38 - 15 19 28 442
24 200 0.33 - 81 12 202 372
24 250 0.37 - 11 15 232 412
24 300 0.40 - 13 17 262 432
24 350 0.43 - 15 19 28 452
30 150 0.34 - - 91 172 332
30 200 0.38 - 81 12 202 372
30 250 0.42 - 11 15 232 402
30 300 0.45 - 12 16 252 422
30 350 0.49 - 15 19 282 442
36 150 0.38 - - 9 172 332
36 200 0.42 - 81 12 202 372
36 250 0.47 - 10 14 232 402
36 300 0.51 - 12 17 252 422
36 350 0.56 - 15 19 282 452
42 150 0.41 - - 9 162 322
42 200 0.47 - 8 12 202 372
42 250 0.52 - 10 14 232 402
42 300 0.57 - 12 172 252 422
42 350 0.63 - 15 19 282 452
48 150 0.46 - - 9 172 332
48 200 0.52 - 8 122 202 372
48 250 0.58 - 10 142 232 402
48 300 0.64 - 12 172 252 422
48 350 0.70 - 15 192 282 442
54 150 0.51 - - 9 172 332
54 200 0.58 - 8 122 202 372
54 250 0.65 - 10 142 232 402
54 300 0.72 - 13 172 252 432
54 350 0.79 - 15 192 282 452
60 150 0.54 - 51 9 172 332
60 200 0.61 - 8 122 202 372
60 250 0.68 - 10 142 232 402
60 300 0.76 - 13 172 252 432
60 350 0.83 - 15 192 282 452
64 150 0.56 - 51 9 172 332
64 200 0.64 - 8 122 202 362
64 250 0.72 - 10 152 232 402
64 300 0.80 - 13 172 252 432
64 350 0.87 - 15 192 282 452

1 Minimum allowable depth of cover is 3’.

2 Denotes the depths of cover resulting from the pipe thickness being governed by deflection in the design; these covers are greater due to the design deflection of 5% for flexible-lined pipe instead of 3% for cement-lined pipe.