Ductile iron pipes can be used for conveying sewage in gravity transmission. High alumina cement (HAC) mortar applied at the factory, conforming to IS 8329:2000, is used as the lining material. The cement mortar lining should satisfy the type tests for chemical resistance and abrasion resistance, conforming to ISO:7186 and/or EN:598.
Type test for chemical resistance to effluents as per ISO:7186/EN:598
Result of the type test for chemical resistance to effluents as per EN:598
Sample No. 1 (DN 400 pipe assembly sample) was exposed for six months to an acid solution and an alkaline solution, generally in accordance with Clause 7.7 for type “Istra 50” high alumina cement mortar lining. After six months, the following conditions were met:
| There was no visible cracking, blistering or disbonding of the epoxy- based coating (acid solution and alkaline solution). |
Pass |
| pH3 solution: Deviation from original thickness of cement mortar lining (mm). Specified: 0.2 max, Actual: 0.14. |
Pass |
| Hardness of rubber gasket (Shore A): Heel Specified: 76 to 84, Actual: 80. Bulb Specified: 46 – 55, Actual: 54-55. |
Pass |
| Tensile strength of rubber gasket (N/mm2): Heel Specified: 9 min, Actual: 9.5-10.1. Bulb Specified: 9 min, Actual: 9.9-10.7. |
Pass |
| Elongation of rubber gasket (%): Heel Specified: 125 min, Actual: 150-175. Bulb Specified: 375 min, Actual: 450. |
Pass |
| There was no visible cracking of the rubber gasket. | Pass |
Sample No. 2 (DN 450 pipe assembly sample) was exposed for six months to an acid solution and an alkaline solution, generally in accordance with Clause 7.7 for type “Calcoat RG” high alumina cement mortar lining. After six months, the following conditions were met:
| There was no visible cracking, blistering or disbonding of the epoxy-based coating (acid solution and alkaline solution). |
Pass |
| pH3 solution: Deviation from original thickness of cement mortar lining (mm). Specified: 0.2 max, Actual: 0.11. |
Pass |
| Hardness of rubber gasket (Shore A): Heel Specified: 76 to 84, Actual: 80-81. Bulb Specified: 46 – 55, Actual: 51. |
Pass |
| Tensile strength of rubber gasket (N/mm2): Heel Specified: 9 min, Actual: 10.9-11.4. Bulb Specified: 9 min, Actual: 9.8-10.8. |
Pass |
| Elongation of rubber gasket (%): Heel Specified: 125 min, Actual: 250-275. Bulb Specified: 375 min, Actual: 425-475. |
Pass |
| There was no visible cracking of the rubber gasket. | Pass |
Result of type test for abrasion resistance as per EN:598
| When tested in accordance with Clause 7.8, Sample No. 1 (DN 400 pipe assembly) and Sample No. 2 (DN 450 pipe assembly) had an abrasion resistance of less than 0.6 mm. |
Pass |
| Sample No. 1 – Type Istra 50 depth of abrasion (mm). Specified: 0.6 max. Actual: 0.46. |
Pass |
| Sample No. 2 – Type Calcoat RG depth of abrasion (mm). Specified: 0.6 max. Actual: 0.55. |
Pass |
Chemical requirements of calcium aluminate cement
As per code BS EN 14647:2005, the properties of calcium aluminate cement should conform to the requirements listed below:
Note: (a) Requirements are given as a percentage by mass of the final cement
(b) Expressed as Na2O equivalent (Na2O + 0.658 K2O)
Conclusion
Pipe material should be considered for selection only after undertaking a life-cycle cost analysis. Ductile iron pipes with HAC lining are most suitable for use in cities where we cannot lay sewer lines repetitively due to the need for deep road excavations, unavailability of adequate road width, traffic issues, and other public utility constraints. It is desirable to use ductile iron pipes with HAC lining, considering a design period of 50 years.
Sabarna Roy, Senior Vice President, and Basanta Bera, Assistant Manager, Business Development, Electrosteel Castings Limited