In this post I want to share how to check if a horizontal pipe carrying liquid is full or partially full. We can use the following criteria to check:

- The pipe is full if:
**Q/d**^{5}≥ 10.2 - The pipe is partially full if:
**Q/d**^{5 }< 10.2

For partially full pipe, we need to do partially full flow analysis as follows.

**x = ln (Q/d ^{2.5})**

Then we calculate height of liquid in the pipe using the following equation:

**H/D = 0.446 + 0.272x + 0.0397x ^{2} – 0.0153x^{3} – 0.003575x^{4}**

Equivalent diameter (D_{e}) is calculated by the following equation:

**D _{e}/D = -0.01130 + 3.040 (H/D) – 3.461 (H/D)^{2} + 4.108 (H/D)^{3} – 2.638 (H/D)^{4}**

Where:

D = pipe diameter, ft

D_{e} = equivalent diameter, ft

H = height of liquid in the pipe, ft

Q = flow rate, gpm

d = pipe diameter, in

q = flow rate, ft/s

u = velocity, ft/s

D_{e} is substituted for D in subsequent flow analysis.

I made a simple spreadsheet to check pipe carrying liquid is full or partially full, what the liquid height is, and pipe equivalent diameter. Please check and download if you find this useful.

*Download: calculation of pipe carrying liquid is full or partially full.*

**Reference:**

Branan, Carl, *Rules of Thumbs for Chemical Engineers*, 2005, Gulf Professional Publishing.