Class K7 DN300 ductile iron pipe has a nominal diameter of 300 mm (12″) and is designed to operate at a working pressure of 7 bar (approximately 100 psi). It is made from ductile iron of grade 500-7 (with a minimum tensile strength of 500 MPa and minimum elongation of 7%) or grade 450-10 (with a minimum tensile strength of 450 MPa and minimum elongation of 10%).
The pipe features a smooth cement-mortar lining on the inside and a protective external coating of zinc (≥130 g/m²) and bitumen (70 μm). An optional loose polyethylene sleeve can also be added. These features, along with modern installation practices, contribute to a design life of over 100 years.The pipe complies with international standards such as ISO 2531, EN 545/EN 598, ISO 4179, and AWWA C150/C151, making it widely accepted around the world.
Ductile iron pipe’s strength, resilience, and corrosion protection make Class K7 DN300 ideal for:
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Potable water distribution: Centrifugally cast DI pipe is the preferred choice for drinking water mains, offering low leak rates and smooth flow owing to its cement‑mortar lining.
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Sewerage and pressure sewer systems: Conforms to BS EN 598 for wastewater, handling internal surges at pump stations without joint failure.
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Fire protection mains: Meets NFPA safety factors with burst pressures > 3× working pressure, ensuring reliable hydrant supply.
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Industrial process lines: Chemical plants and refineries use custom epoxy or bitumen coatings on Class K7 pipes to withstand aggressive media and thermal cycling.
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Trenchless and subsea installations: Push‑on and ball‑and‑socket restrained joints eliminate thrust blocks, reducing excavation in horizontal directional drilling and river crossings.
Service Life
Studies and industry data converge on a century‑plus lifespan for properly protected DI pipelines:
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≥ 100 years with cement‑mortar lining and loose polyethylene sleeve encasement (LPS).
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50–60 years for zinc/bitumen coated pipes without LPS in typical soils.
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Compared to alternatives: PVC mains generally last ≈ 50 years, making DI a longer‑term investment.
Installation and Connections
Class K7 DN300 supports versatile joint systems:
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Push‑on (Tyton/T‑type): Elastomeric gaskets form water‑tight seals and permit up to 4–5° angular deflection per joint, accommodating alignment curves without leakage.
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Mechanical (MJ): Bolted restraint devices resist thrust at bends and tees, eliminating separate concrete thrust blocks and reducing trench depth.
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Flanged ends: Standard ISO/AWWA flanges allow direct connection to valves, hydrants, and fittings for easy integration and maintenance.
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Ball‑and‑socket restrained: Ideal for submerged or unstable ground, these joints resist axial separation under high hydrostatic loads.
International Standards
Class K7 DN300 pipes meet the following global specifications:
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ISO 2531:2009 – Ductile iron pipes for water supply applications.
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EN 545:2010 – DI pipes and fittings for potable water.
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EN 598:2007 – DI pipes and fittings for sewerage systems.
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ISO 4179 – Cement‑mortar lining requirements.
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AWWA C150/C151 – Design and centrifugally cast DI pipe standards in North America.
Price Comparison with Other Series
Indicative pricing (USD per metric ton, 6 m lengths; subject to volume, coating, and region):
| Class | Working Pressure | Price Range (USD/MT) |
|---|---|---|
| K7 | 7 bar | 400–900 |
| C30 | 30 bar | 460–560 |
| K8 | 8 bar | 400–720 |
| K9 | 9 bar | 478–531 |
Key Advantages
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Mechanical resilience: Manufactured from ductile iron grade 500‑7 or 450‑10 (tensile ≥ 450–500 MPa; elongation ≥ 7–10%), providing superior impact and fatigue resistance.
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Corrosion protection: Cement‑mortar interior lining (Hazen‑Williams factor 130–151) plus zinc/bitumen exterior and optional LPS deliver decades of corrosion control in aggressive soils.
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Hydraulic efficiency: Smooth lining minimizes head loss, reducing pumping energy and operational costs over a long service life.
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Installation flexibility: Push‑on and restrained joints accommodate ground movement and seismic loads without extensive thrust blocks.
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Sustainability: Made from ≥ 90% recycled iron; fully recyclable at end‑of‑life; environmentally preferable material.
Frequently Asked Questions
Q1: What does “Class K7” indicate?
A1: A nominal pressure rating of 7 bar (≈100 psi) per ISO 2531 designations.
Q2: Why choose DN300 (12″)?
A2: DN300 balances high flow capacity for trunk mains with manageable handling, fitting availability, and pump station integration.
Q3: How is corrosion mitigated?
A3: Through cement‑mortar lining per ISO 4179 and external zinc (130 g/m²) + bitumen (70 μm) coatings; optional loose polyethylene sleeve (ANSI/AWWA C105) further protects in corrosive soils.
Q4: What joint types are available?
A4: Push‑on (Tyton/T‑type), mechanical restrained (MJ), flanged, and ball‑and‑socket restrained joints, selected by project needs for speed, cost, and thrust resistance.
Case Studies
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Wilkes‑Barre, Pennsylvania (PA): Pennsylvania American Water replaced 5.5 km of aging mains with 8″ and 12″ Class K7 ductile iron, reducing leaks by 90% and achieving a 50‑year lifespan extension.
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St. Louis County, Missouri (MO): Missouri American Water installed a 1.6 km section of 16″ (≈DN400) ductile iron petroline to replace 1950s‑era steel, cutting maintenance costs by 40% and ensuring reliable service under variable soil conditions.
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 | ….. |
