Fortunately, many philosophies are already summarized in the parameter that clearly defined. For instance, to avoid deposit at drain line we need velocity more than 1.1 fps, to avoid surge on the reciprocating compressor we need suction velocity less than 40 fps etc. To achieve optimal operating cost of cooling water pump, the water header pressure drops shall be less than about 0.3 bar/100 m. Etc. Those data parameter are very useful. It’s helpful for us to imagine our pipe condition.
It is not surprise for me that those parameters are not the exact value. I mean, the value is not always 1.1 fps, 40 fps. Etc. Here simple example, for liquid sub cooled, suction pump has parameter of maximum velocity 8 fps, we may choose to use 10 pipe size with the velocity 8.1 fps rather than 12 inch with the velocity 7.0 fps. I just say ’may’, not ‘better’ because it is depends on some consideration. Please continue reading. I hope you got it after read this fully article
Many companies agreed only for two phases flow parameter. They agreed to avoid slug flow and erosion with same parameters called flow induce vibration and erosion. We can refer to the formula stated in API 14E for calculate erosional velocity-[erosional velocity = Constant/mix density^0.5]-. In some cases we cannot avoid slug flow due to erosional velocity limitation. In this case, good understanding of line sizing philosophy is helpful. Actually, slug flow can be acceptable if we can make the pipe stand using more strength support. But, erosion is something we cannot avoid without change the pipe size. Once erosion continued happen, your pipe is under dangerous condition. So, we shall use flow regime and an erosional velocity for limitation of acceptability pipe size for two phase line.
At proposal stage, we need to optimize the pipe size to achieve competitive cost.
For example, for large size duplex gas line, carefully reviewing of the line sizing result is very important. Optimize if it is possible. No doubt, the cost will be significantly reduced if we can optimize duplex or stainless steel pipe with many valve installed along that pipe. We can choose the lower pipe size as long as it is reasonable and the philosophy is achieved.
Other example, for air system, there are small pipe size in the system, and the material usually CS or CS galvanized is used. If you have short time of proposal duration, I suggest you to check the adequacy only. Don’t waste your time to optimize this small line.
Sometimes, we are also able to optimize the pipe size for some cases depend on the service condition. Here I give an example.
Look at this picture.
The service line is fuel gas to burner, the line in high pressure, with 8 inch pipe size. If you conduct line sizing calculation, and the result show that
That’s all I can share to you, let’s keep in our mind, line sizing is not just inputting the data, and then looking at column
Hopefully, this article is useful for us. Please correct me if I am wrong. Thank you.