Class K7 DN250 ductile iron pipe is a robust, 250 mm (10″) nominal‐diameter pipeline solution engineered for medium‑pressure applications up to 7 bar (≈100 psi). With tensile strength ≥ 420 MPa and a minimum yield of 300 MPa, these pipes combine mechanical resilience with a smooth cement‑mortar lining and zinc/bitumen external coatings to deliver over 100 years of service life under modern corrosion‑control measures. Standard 6 m lengths use push‑on, mechanical, or self‑restrained joints—simplifying installation across diverse terrains and trenchless methods. Compliant with ISO 2531, EN 545, EN 598, and AWWA C150/C151, Class K7 DN250 balances cost and performance: typical prices range USD 400–720/MT for K7 vs. USD 600–700/MT for higher‑grade C30 or K9 classes. Key advantages include hydraulic efficiency, joint flexibility, and sustainability (≥ 90% recycled iron). Below is a deeper dive into each dimension:
Application Scenarios
Class K7 DN250 pipes serve a wide array of functions:
-
Municipal water distribution: Handles potable water mains in cities, offering low friction losses and consistent flow rates thanks to its cement‑mortar lining.
-
Pressure sewage and wastewater systems: Resists internal surges at pump stations and carries effluent with minimal maintenance.
-
Agricultural irrigation: Withstands soil stresses and UV exposure when sealed with polyethylene encasement, ensuring decades of uninterrupted crop watering.
-
Fire protection: Meets NFPA requirements with burst pressures > 3× working pressure, securing reliable hydrant supply.
-
Industrial process lines: Custom external coatings (epoxy, bitumen) and restrained joints support chemical plants and refineries under fluctuating loads.
Service Life
Advanced lining and coating systems extend the DN250 lifecycle:
-
Cement‑mortar lining + PE encasement: ≥ 100 years in moderate soils.
-
Zinc/bitumen coating only: ≈ 50 years under normal conditions.
-
Unprotected in aggressive soils: 21–40 years, underscoring the ROI of modern corrosion control.
| Protection System | Estimated Service Life |
|---|---|
| Cement‑mortar + PE encasement | ≥ 100 years |
| Zinc/bitumen coating | ≈ 50 years |
| No external protection, aggressive soil | 21–40 years |
Installation and Connections
DN250 Class K7 supports multiple joint types for flexibility and speed:
-
Push‑on (T‑type): Elastomeric gaskets create leak‑tight seals with up to 5° deflection per joint, ideal for curved alignments.
-
Mechanical (MJ): Bolted restraints provide thrust resistance without concrete blocks, reducing trench depth.
-
Self‑restrained (ball‑and‑socket): Simplifies subsea or river crossings, resisting separation under hydrostatic loads.
-
Flanged ends: Enables direct valve/fitting integration per ISO/AWWA flange standards.
International Standards
Class K7 DN250 pipes adhere to:
-
ISO 2531 (ductile iron pipes for water).
-
EN 545 (drinking water applications) and EN 598 (sewerage).
-
ANSI/AWWA C150/C151 (centrifugally cast design and lining).
Price Comparison with Other Series
Indicative costs (USD per metric ton) illustrate K7’s competitive position:
Key Advantages
-
High mechanical strength: Tensile ≥ 420 MPa; yield ≥ 300 MPa; elongation ≥ 10%.
-
Durable corrosion protection: Internal lining per ISO 4179; external zinc (≥ 130 g/m²) + bitumen topcoat per ISO 8179.
-
Hydraulic efficiency: Smooth lining reduces head loss, lowering pumping energy costs.
-
Flexibility under load: Joints absorb ground movement and seismic shifts without leaks.
-
Sustainability: ≥ 90% recycled iron content; fully recyclable at end‑of‑life.
Frequently Asked Questions
Q1: What does “Class K7” mean?
A1: It signifies a design working pressure of 7 bar (≈100 psi) under ISO 2531 standards.
Q2: Why choose DN 250?
A2: Offers high flow capacity in trunk mains while remaining manageable for handling and jointing.
Q3: How is corrosion controlled?
A3: By combining cement‑mortar lining and external zinc/bitumen coatings, plus optional polyethylene sleeve per ANSI/AWWA C105.
Q4: Can Class K7 be used in fire mains?
A4: Yes—burst pressures exceed 3× working pressure, meeting NFPA safety factors.
Case Studies
-
Arizona PVC ban: Eight major Arizona utilities require ductile iron (often Class K7) for new mains, citing life‑cycle reliability and reduced leak rates.
-
Sand Hollow Regional Pipeline, Utah: Joint deflection in DN250 pipes navigated varied soils and elevations without damage in Phase A of the 114 km pipeline.
-
German mining subsidence: DN250 K9 pipes (same diameter and similar joint design) withstood 3 m‑wide sinkholes caused by coal extraction, maintaining integrity under deflection up to 4°.
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 | ….. |
