March 2014 Page 1 of 3 © Chart Inc.

CHART CRYOGENIC TIP #5 Pipe Gas Flow Pressure Drop & Maximum Flow

We use the Air Pressure Drop In Pipe Chart ("APDP Chart") shown on the next page, to approximate the pressure drop caused by the flow of atmospheric nitrogen, argon, or oxygen gases through a straight section of pipe and to determine the maximum flow attainable through that same section. Because the gravity of these three atmospheric gases are very close to the specific gravity of air, this chart will be a very handy tool in sizing pipe or tube for your gas delivery system. Below you will also find a few examples on how to use this chart.

Example 1: Estimate Pressure Drop in a Pipe Line psi = Pressure per Square Inch

psia = Pressure per Square Inch Absolute CFM = Cubic Feet per Minute SCFH = Standard Cubic Feet per Hour SCFM = Standard Cubic Feet per Minute or CFM at 60º F and 14.7 psia ID = Inside Diameter OD = Outside Diameter

EXAMPLE 1 PARAMETERS: a. 200' pipeline from bulk tank to cutting process

b. One elbow in this 200' line c. Require 3,600 SCFH of Ni gas at 50 psi d. Bulk tank is operating at 125 psi What ID of pipe will we need to meet this need?

First, let's figure the pressure drop in the 200' of line. In the APDP Chart (shown on Page 2) you will note that the left column is shown in CFM at 60º F and 14.7 psia. Therefore, we will need to change our flow from SCFH to SCFM. Since there are 60 minutes to an hour, 3600 SCFH equals 60 SCFM. Now, go down the left column to 60 SCFM and following horizontally to the right, the chart shows the pressure drop per 100' per listed pipe sizes (see area in red box on chart). NOTE: There are no pressure drop values listed on the chart for the ¼" and ⅜" pipe sizes, which means the pressure drop for those two pipe sizes would be too great to use with the 3600 SCFH flow.

• ½" pipe will give you 12.2 psi pressure drop per 100' of pipe. We have 200' so ½" ID pipe would give you a 24.4 psi pressure drop. If there are elbows in the line, then a good rule of thumb is to double the pressure drop, so you would have approximately 48.8 psi (24.4 x 2) per 200' of pipe. This means that, since we are running the bulk tank at 125 psi, the pressure of the gas reaching your final line regulator will be 76.2 psi (125 minus 48.8). You would need to verify it is possible to obtain a pressure-reducing regulator that would flow at 3600 SCFH with an inlet pressure of 76.2 and an outlet pressure of 40 psi.

• ¾" pipe will give you 2.85 psi pressure drop per 100' of pipe. With elbows this turns to 5.7 psi (2.85 x 2) per 100'. Since we have 200' of pipe, total pressure drop will be 11.4 psi (5.7 x 2). The gas pressure at the inlet of your final line regulator would then be 113.6 psi (125 minus 11.4). You will just need to pick a final line regulator that will flow 2600 SCFH with an inlet pressure of 113.6 psi and outlet of 40 psi. However, you are more likely to find a final line regulator that would flow 3600 SCFH with that pressure differential.

Since there are also probably valves and fittings which will add to the pressure drop in this line, we can assume that 1" ID pipe would be a better fit for this application.

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This Air Pressure Drop in Pipe chart is included in Chart's Data Book. Email literature@chartindustries.com with your name, company, mailing address, and request for a copy of the Data Book.

APDP CHART

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NOTE: The APDP Chart on Page 2 lists flow through PIPE, not TUBE. The Inside Diameter ("ID") of pipe is larger than the ID of copper or stainless steel tube because pipe size is the ID of pipe, while tube is sized by the Outside Diameter ("OD"). Therefore, if you are using 1" OD copper tube, you will need to use the ¾" schedule 40 pipe on the APDP Chart when performing your pressure drop or flow sizing calculation.

Schedule 40

Pipe Size ID

K Copper

OD ID

¼" 0.364" ¼" 0.180"

⅜" 0.493" ⅜" 0.277"

½" 0.622" ½" 0.402"

¾" 0.824 ¾" 0.620"

1" 1.05" 1" 0.870"

1 ¼" 1.38" 1 ¼" 1.106"

1 ½" 1.61" 1 ½" 1.356"

2" 2.06" 2" 1.834"

2 ½" 2.47" 2 ½" 2.310"

3" 3.07" 3 2.782"

Example 2: Find the Maximum Flow Through a Tube Line

psi = Pressure per Square Inch psia = Pressure per Square Inch Absolute CFM = Cubic Feet per Minute SCFH = Standard Cubic Feet per Hour SCFM = Standard Cubic Feet per Minute or CFM at 60º F and 14.7 psia ID = Inside Diameter OD = Outside Diameter

EXAMPLE 2 PARAMETERS: a. 200' from bulk tank to cutting process b. Line is 1" copper tube c. One elbow in 200' line d. Bulk tank is operating at 125 psi

e. Cutting equipment requires 60 psi What is the maximum flow we can get from this line?

Pipe is sized by the Inside Diameter and tube is sized by the Outside Diameter. The APDP Chart shows the flow through a pipe line but in this example we are using a tube line, so we must first determine the equivalent pipe size to refer to on the APDP chart. To assist, the chart to the left shows IDs of pipe and tube, we can see that a 1" OD copper tube is closest in ID to ¾" pipe (see blue boxes).

Now we know to look at the APDP Chart on Page 2 for ¾" pipe. We see the vertical column (in blue box) starts with a pressure drop of 0.027 psi for a flow of 5 SCFM (or 300 SCFH), and ends with 30 psi pressure drop at 200 SCFM (or 12,000 SCFH). So, the highest flow possible for ¾" pipe is 12,000 SCFH.

We still have to look at the pressure drop in that line. We need 60 psi at the cutting equipment and on the chart we see a pressure drop of 30 psi per 100' of pipe. Remember, there is an elbow in that line so we need to double that pressure drop. Potentially we could see 60 psi pressure drop per 100' of 1" OD tube, or 120 psi for 200' of 1" OD tube. We would have to increase the pressure in the bulk tank to 245 psi (125 x 2) in order to have 60 psi at the cutting equipment.

Per the APDP chart, with 100 SCFM (or 6000 SCFH), you will get 7.69 psi pressure drop per 100'. So for our 200' of tubing with one elbow, we would have a 30.7 psi (4 x 7.69) pressure drop.

Therefore the pressure of the gas at the final line regulator inlet will be 94 psi (125 – 30.7). If the final line regulator will flow 6000 SCFH with a 34 psi (94 minus 60) pressure differential, then 6000 SCFH

is the maximum flow for your application.

If your regulator cannot handle that small of a pressure differential, you will need to keep dropping the flow until there is sufficient pressure differential for the final line regulator to handle the flow.

If you have any questions, you may always call Chart's Customer Service Department for more information at 800.400.4683.

Submitted by Jim Rosenbush Technical Service Representative

Chart Inc. Distribution & Storage Group