A recent hydraulic flow test on a 97-year old distribution main demonstrated the longevity of cement-mortar lined (CML) iron pipe, and the consistent flow efficiency that translates into pumping cost savings.
With energy costs among the higher factors of consideration in water distribution systems, flow efficiency translates to significant savings, year over year – and upward to 100 years.
Longevity is an important consideration in pipeline decision making. The longer a pipe serves, the more cost-effective it becomes. The water infrastructure in the United States dates to the early 1800s, with some of those original pipelines still serving. Experiences from operating those systems help guide research and often produce innovative opportunities for improvement.
First CML Lined Pipe: Charleston, South Carolina.
One such innovation occurred in 1922 in Charleston, South Carolina where, on Grove Street, the Charleston Water System installed the first iron pipeline to be provided with a cement-mortar lining. The lining was intended to improve the quality of the water by preventing the pipe from experiencing oxidative reactions in unlined metallic pipe. As an added benefit, the lining helped reduce the energy required to pump water through the pipe by improving its hydraulic character. As seen in Charleston, the improved flow provided by the cement-mortar lining maintains this benefit over nearly one century of service.
The Ductile Iron Pipe Research Association (DIPRA) had evaluated this iconic cement-mortar lined pipe in three previous flow tests conducted after 51, 59 and 73 years in service in Charleston. Using the Hazen-Williams equation, the most popular model to predict energy loss in pumped water systems, the empirical constant, C, was calculated. A dimensionless number, C characterizes the relative smoothness of the inside pipe wall. The higher the value for C, the lower the energy loss.
In the three previous tests on this pipeline, the value for C held between 130 and 131. Those results were added to results from dozens of other similar tests conducted on cement-mortar lined iron pipes of various ages throughout the U.S. The average value of those data is the basis for DIPRA’s recommendation of C = 140 for cement-mortar lined Ductile iron pipe.
The Latest Test
In November 2019, DIPRA, in cooperation with the Charleston Water System, engaged M.E. Simpson Company to conduct a flow test on the 8-in. iron pipe that was the first to be provided with a cement-mortar lining.
The M.E. Simpson Company conducted the tests on the Grove Street pipeline – the same section that had been previously tested. The procedure was to determine the loss in energy over that section of the pipeline through direct measurement of the inside diameter of the pipe, the velocity of the water at that location and the difference in pressure and elevation between the two ends of the pipe section. Knowing these, the Hazen-Williams C could be calculated and compared to previous results.
There were five consecutive tests run, with the average result being C = 140.
Note that the results after 97-years were quite a bit better than previous results. Part of the reason for this improvement may be attributed to the state-of-the-art equipment used by M.E. Simpson. Their differential pressure recorder has a precision measured to 0.001-in., which is an improvement over the equipment used in previous tests.
Also a consideration is the program of flushing the mains that is part of Charleston Water System’s asset management protocols. The results provided definitive confirmation that the cement-mortar lining put in the 8-in. iron pipeline installed in 1922 in Grove Street in Charleston, SC has provided outstanding service for nearly one century.
Data for Decision-Making
The longevity of cement-mortar linings has been demonstrated through several studies. These results add to the body of data that is used by the Ductile iron pipe industry to provide recommendations that water professionals can use to realize the true value of their iron pipes.
When we discuss our underground water infrastructure, we ask it to do a lot. We need a very manageable system that minimizes emergencies and provides quality water at acceptable costs; and we want it to serve for an exceedingly long time without the kind of renovations that above-ground facilities would require.
The flow tests conducted in 2019 on this 97-year old cement-mortar lined iron pipe instill confidence in the long-lasting efficacy of cement-mortar lined iron pipe, and its modern successor, ductile iron pipe.
L. Gregg Horn, P.E., is vice president of technical resources at DIPRA. He serves on industry standards-making committees; directs technical research projects on a variety of applications-based topics, such as corrosion control and design of Ductile iron pipe; and leads a team of regional engineers who provide personal technical services to water/wastewater utility personnel and consulting engineers.