Understand Your Flow Profile for Real-World Flow Meter Accuracy

As explained in my last post on flow conditioning, distorted flow profile is a common problem in “real world” flowmeter applications. In some cases, customers can live with a distorted flow profile because they are using flow meters for a relative measurement of flow, rather than an absolute measurement of flow. In cases where the customer is looking for an absolute measurement of flow and the flow profile is distorted, improvements to the measurement can be made by performing a traverse.

To perform a traverse, drill into the pipe on the horizontal plane and then the vertical plane. Fittings are welded over the holes to support the test probe as it is traversed from one side of the pipe to the other. Depending on the diameter of the pipe, up to 10 measurements of flow should be made. The spacing between the measurements should be equally divided. This data can then be used to draw a two-dimensional map of the flow profile along this plane. Then, by again repeating this process in the other plane, a detailed map of the actual flow profile in the pipe of interest can be generated. Upon completion of the traverse, the data gathered can be studied to determine the optimum spot to locate the permanent measurement point from which flowmeters will read the average flow in the pipe.

In some cases, especially in large pipes, the flow may be too complex to be accurately measured with a single probe, even after traversing. Distorted flow profiles in large pipes can often involve large scale swirls, which are impossible to measure accurately with a single measurement point. So, in cases like these, the ultimate solution is to install a multi-point system, which I will talk about in a later post.