C Factor Testing
Why am I seeing an increase in my energy use at wastewater pump stations?
Pump stations are often designed using a Hazen Williams C Factor of 120 for new force mains. Over time, debris and a slime layer build up on the interior surfaces of wastewater force mains, resulting in a reduction of the C Factor. As the C factor decreases, the power required to pump the wastewater increases.
V&A has measured the C Factor on many Force Mains in many areas, including California, Nevada, and Hawaii. Our data shows that the measured C Factors across Force Mains range between 80 and 90.
The figure below shows the measured C Factors relative to the operational flow velocities measured in the force mains.
A detailed paper presenting the data written by V&A’s Mike Johannessen, P.E and Jose Villalobos, P.E. was published by ASCE for the 2014 Pipeline Conference.
C Factor testing is a relatively inexpensive, noninvasive, nondestructive test (NDT) method that can be used to assist agencies in gauging the condition of the force mains.
One of the major benefits of this test procedure is that the force main does not need to be taken out of service.
This test method can be categorized as a primary screening tool. The following are some benefits of this screening tool.
Condition assessment: Condition assessment activities can be focused on force mains with low C values (increased pipe roughness) if there is a reason to suspect that this might be due to internal corrosion or air pockets (which promote corrosion). Especially in conjunction with other information, C-factor test results can help to quantify the detrimental effect that internal tuberculation (roughness due to corrosion) and slime layers may have. C-factor testing can also allow for extrapolation of limited internal condition data to other force mains with similar hydraulic performance.
Optimization of operations: C-factor test results can be used in many ways, including the following:
Determining if the pipe friction loss is acceptable, somewhat high, or unacceptably high. Part of this judgment involves considering the feasibility of cleaning the force main to restore smoothness and how much improvement might be expected.
Energy consumption or cost analysis. In conjunction with information about what is increasing the pipe roughness, dosing strategies may be considered or reconsidered with respect to pipe friction (versus solely odor control, etc.).
Monitoring the trend in C-value changes by repeating tests on a regular basis to monitor performance over time. This type of monitoring is already done by many operators, but the results may not be distilled into a form (such as a C value) that can be tracked over time, compared with other force mains, etc.
Finding performance issues: Sometimes, a pump station and its force main are known to be performing poorly, but the cause is not always known. C-factor testing can determine whether the issue is excessive pipe friction. Additional measurements can also be added to the test setup to measure pump performance and station losses, further narrowing down the source of a known issue.
Hydraulic analysis: Capacity analysis, expansion projections, future designs, etc., can be based on actual conditions rather than assumptions.
Sustainability: Management of the increase in C values over time can result in a significant reduction in the amount of power required to pump wastewater over time. To borrow a saying from the management world, “If it can be measured, it can be managed.”
C Factor analysis is one of the ways we support our customers in achieving the most effective system performance. Learn more about our Condition Assessment and Flow Monitoring Services.