Class 51 ductile iron pipe is a special-thickness class defined in ANSI/AWWA C150/A21.50 and C151/A21.51, offering wall thicknesses intermediate between Classes 50 and 52 for sizes 3″–24″ and designed to withstand rated working pressures plus a 100 psi surge allowance. It is often mandated as the minimum thickness for pipes 14″ and larger in many municipal water-main specifications, ensuring robustness for transmission mains . With centrifugally applied cement-mortar lining (ANSI/AWWA C104) and optional polyethylene encasement (ANSI/AWWA C105), Class 51 pipelines routinely exceed 100 years of service life in normal soils. Installation is flexible—supporting push-on (C111), mechanical (C110), restrained and flanged joints—facilitating rapid, leak-tight assembly for potable, wastewater and industrial systems. Fully compliant with AWWA C150/C151, C104/C105, C110/C111 and international ISO 2531, EN 545/598 standards, Class 51 offers competitive life-cycle performance compared to Classes 52, 53, 150, 250 and 350.
Application Scenarios
Class 51 ductile iron pipe excels in:
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High-pressure transmission mains (14″+): Meets minimum thickness requirements for large-diameter pipelines in suburban and inter-city networks.
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Water treatment plant outlets: Withstands continuous flow and occasional surge events, preserving integrity over decades.
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Gravity and force sewage mains: Cement-mortar lining resists tuberculation in aggressive wastewater applications, reducing cleaning cycles.
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Irrigation and agricultural conveyance: Low Hazen–Williams friction factor (C≈140) cuts pumping energy vs. PVC alternatives.
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Industrial process loops: Flanged joints allow rigid connections to pumps and valves in chemical and power plants.
Service Life
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100+ years in typical burial conditions when lined and encased per AWWA standards.
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Cement-mortar lining virtually eliminates internal corrosion, maintaining hydraulic capacity over a century.
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Life-cycle cost analyses show DI mains outperform PVC and other materials in total cost of ownership over 100 years.
Installation and Connection
Push-On & Mechanical Joints
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Push-on joints (ANSI/AWWA C111) feature a simple rubber gasket for fast, trench-side assembly without bolting.
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Mechanical joints (ANSI/AWWA C110) use a gland and bolts compressing an elastomeric gasket; rated up to 350 psi for restrained service.
Restrained & Flanged Systems
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Restrained joints (e.g., Field-Lok®) lock spigot and bell to resist thrust forces, reducing need for concrete thrust blocks.
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Flanged ends (ANSI B16.1/250 psi or AWWA C207) bolt directly to valves, pumps and metering, enabling rigid, dismantlable connections.
Corrosion Protection
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Internal lining: Cement-mortar per ANSI/AWWA C104 creates a high-pH barrier against tuberculation.
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External coatings: Options include bonded zinc, asphaltic enamel or epoxy; polyethylene sleeving per AWWA C105 in aggressive soils .
International Standards
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ANSI/AWWA C150/A21.50 & C151/A21.51: Pressure-class thickness design and centrifugal casting.
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ANSI/AWWA C104/A21.4 & C105/A21.5: Cement-mortar lining and PE encasement specifications.
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ANSI/AWWA C110/A21.10 & C111/A21.11: Mechanical and push-on joint requirements.
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ISO 2531:2012, EN 545, EN 598: International benchmarks for DI pipes and fittings.
Comparative Parameters (Classes 51, 52, 53, 150, 250, 350)
| Class | Rated Pressure | Surge Allowance | Joint Types | Diameters |
|---|---|---|---|---|
| 51 | Special-thickness (adequate for rated pressure) | 100 psi | Push-on, MJ, restrained, flanged | 3″–64″ (≥14″ min spec) |
| 52 | 200 psi | 100 psi | Mechanical only | 3″–64″ |
| 53 | 250 psi | 100 psi | Mechanical only | 3″–64″ |
| 150 | 150 psi | 100 psi | Push-on, MJ, restrained, flanged | 3″–64″ |
| 250 | 250 psi | 100 psi | Push-on, MJ, restrained, flanged | 3″–64″ |
| 350 | 350 psi | 100 psi | Push-on, MJ, restrained, | 3″–64″ |
Advantages
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Tailored Thickness Control: Class 51 bridges the gap between standard classes for customized wall designs .
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Longevity: Cement-mortar lining and encasement deliver 100+ year lifespan.
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High Strength: Meets AWWA tensile/impact criteria under deep cover and surge loads .
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Joint Flexibility: Multiple joint systems optimize installation speed and reliability.
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Sustainability: Up to 60 % recycled iron content; fully recyclable at end-of-life.
Frequently Asked Questions
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What is Class 51?
A “special thickness” designation in AWWA C150/C151 that specifies intermediate wall thicknesses – often used as the minimum for pipes ≥ 14″. -
How does Class 51 differ from Class 52?
Class 51 has slightly thinner walls (.26″–.41″) than Class 52 (.28″–.44″) for the same diameter, offering marginally lower material cost yet adequate for rated pressures plus surge. -
Can Class 51 handle aggressive soils?
Yes—combine with AWWA C105 polyethylene encasement or epoxy coatings for high-chloride or stray-current protection . -
Which joint type installs fastest?
Push-on joints require minimal excavation and no bolts, reducing trench time. -
What sizes are available?
Nominal diameters from 3″ to 64″, with agency specs often requiring Class 51 for 14″ and larger.
Case Studies
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Charleston, SC (1922–2019): Flow tests on the first cement-mortar lined iron pipe showed a Hazen–Williams C ≈ 131 after 97 years, underscoring DI longevity.
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University of Michigan LCCA: An LCCA comparing 8″ Class 51 mains versus PVC demonstrated lower total cost of ownership over 100 years (internal U-of-M report).
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Huntsville, AL Water Utility: A Black & Veatch study found DI replacement reduced annual O&M by 3 %, equating to $17 million PV savings over 50 years.
ductile iron pipe dimensions
| Pipe body weight （kg/m) | |||||||||||||||
| (Inside Diameter) | (Outside Diameter) | Socket Weight | K8 | K9 | K10 | C class | Total weight of Active Length=6M (kg) | Total weight of Active Length=5.7M (kg) | |||||||
| DN(mm) | OD(mm) | ≈ kg | Class | kg/m | K8 | K9 | K10 | C class | K8 | K9 | K10 | C class | |||
| 80 | 98 | 3.40 | 12.20 | 12.20 | 12.20 | C40 | 9.10 | 77.00 | 77.00 | 77.00 | 58.00 | 73.00 | 73.00 | 73.00 | 55.00 |
| 100 | 118 | 4.30 | 14.90 | 15.10 | 15.10 | C40 | 11.12 | 93.70 | 95.00 | 95.00 | 71.00 | 90.00 | 91.00 | 90.00 | 68.00 |
| 125 | 144 | 5.70 | 18.90 | C40 | 119.00 | ||||||||||
| 150 | 170 | 7.10 | 21.80 | 22.80 | 22.80 | C40 | 16.48 | 138.00 | 144.00 | 144.00 | 106.00 | 132.00 | 138.00 | 137.00 | 101.00 |
| 200 | 222 | 10.30 | 28.70 | 30.60 | 30.60 | C40 | 22.62 | 183.00 | 194.00 | 194.00 | 146.00 | 174.00 | 185.00 | 185.00 | 139.00 |
| 250 | 274 | 14.20 | 35.60 | 40.20 | 44.30 | C40 | 32.63 | 228.00 | 255.00 | 280.00 | 210.00 | 218.00 | 244.00 | 267.00 | 200.00 |
| 300 | 326 | 18.90 | 45.30 | 50.80 | 56.30 | C30 | 43.90 | 290.00 | 323.00 | 357.00 | 282.00 | 278.00 | 309.00 | 340.00 | 269.00 |
| 350 | 378 | 23.70 | 55.90 | 63.20 | 69.60 | C30 | 51.88 | 359.00 | 403.00 | 441.00 | 335.00 | 343.00 | 384.00 | 420.00 | 319.00 |
| 400 | 429 | 29.50 | 67.30 | 75.50 | 83.70 | C30 | 60.78 | 433.00 | 482.00 | 532.00 | 394.00 | 414.00 | 460.00 | 506.00 | 376.00 |
| 450 | 480 | 38.30 | 80.00 | 89.30 | 99.00 | C30 | 73.30 | 515.00 | 575.00 | 632.00 | 472.00 | 492.00 | 550.00 | 597.00 | 450.00 |
| 500 | 532 | 42.80 | 92.80 | 104.30 | 115.60 | C30 | 87.20 | 600.00 | 669.00 | 736.00 | 566.00 | 572.00 | 638.00 | 702.00 | 540.00 |
| 600 | 635 | 59.30 | 122.00 | 137.30 | 152.00 | C30 | 120.62 | 791.00 | 882.00 | 971.00 | 783.00 | 755.00 | 842.00 | 926.00 | 747.00 |
| 700 | 738 | 79.10 | 155.00 | 173.90 | 193.00 | C25 | 142.15 | 1009.00 | 1123.00 | 1237.00 | 932.00 | 963.00 | 1071.00 | 1179.00 | 889.00 |
| 800 | 842 | 102.60 | 192.00 | 215.20 | 239.00 | C25 | 177.07 | 1255.00 | 1394.00 | 1537.00 | 1165.00 | 1197.00 | 1330.00 | 1465.00 | 1112.00 |
| 900 | 945 | 129.60 | 232.00 | 260.20 | 289.00 | C25 | 197.68 | 1521.00 | 1691.00 | 1863.00 | 1446.00 | 1452.00 | 1613.00 | 1777.00 | 1257.00 |
| 1000 | 1048 | 161.30 | 275.00 | 309.30 | 343.20 | C25 | 266.28 | 1811.00 | 2017.00 | 2221.00 | 1759.00 | 1729.00 | 1925.00 | 2118.00 | 1679.00 |
| 1100 | 1152 | 194.70 | 362.80 | 2372.00 | |||||||||||
| 1200 | 1255 | 237.70 | 374.00 | 420.10 | 466.10 | C25 | 373.88 | 2482.00 | 2758.00 | 3034.00 | 2481.00 | 2370.00 | 2632.00 | 2894.00 | 2369.00 |
| 1400 | 1462 | 279.30 | 547.20 | 3563.00 | |||||||||||
ductile iron pipe Mechanical property
| Mechanical Property | |||||||
| Nominal Diameter | Hydraulic test | Tensile strength | Elogation | Yield strength | Bending strength | Brinell hardness | Thickness of cement lining |
| DN(MM) | Mpa | Mpa | % | Mpa | Mpa | HB | mm |
| DN80-DN300 | 5 | ≥420 | ≥10 | ≥300 | ≥590 | ≤230 | 3 |
| DN350-DN600 | 4 | ≥420 | ≥10 | ≥300 | ≥590 | ≤230 | 5 |
| DN700-DN1000 | 3.2 | ≥420 | ≥10 | ≥300 | ≥590 | ≤230 | 6 |
| DN1100-DN1600 | 2.5 | ≥420 | ≥7 | ≥300 | ≥590 | ≤230 | ….. |
