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I asked my AI

1503-44

Petroleum
Jul 15, 2019
6,689
to determine the flow rate of natural gas in a 10-inch steel pipe that is 5000 feet long, with an inlet pressure of 100 psia and an outlet pressure of 75 psia, we can use the Weymouth equation, which is suitable for high-pressure gas pipelines. According to the context, the Weymouth equation is appropriate for pressure ranges above 100 psi and is given by:

$$
Q = \left(\frac{TB}{PB}\right)^{0.5} \cdot \left(\frac{2 \cdot L \cdot (P1^2 - P2^2)}{\pi^{0.5} \cdot D^{4.167}}\right)^{0.5}
$$

Where:
- \( Q \) is the gas flow rate in cubic feet per day (CFD),
- \( TB \) is the base temperature in Rankine (°R),
- \( PB \) is the base absolute pressure in psia,
- \( L \) is the pipeline length in miles,
- \( P1 \) is the inlet pressure in psia,
- \( P2 \) is the outlet pressure in psia,
- \( D \) is the pipe inside diameter in inches.

Given:
- \( TB = 520 \) °R,
- \( PB = 14.76 \) psia,
- \( L = 5000 \) feet (which converts to approximately 0.9524 miles),
- \( P1 = 100 \) psia,
- \( P2 = 75 \) psia,
- \( D = 10 \) inches.

Substituting these values into the equation, we get:

$$
Q = \left(\frac{520}{14.76}\right)^{0.5} \cdot \left(\frac{2 \cdot 0.9524 \cdot (100^2 - 75^2)}{\pi^{0.5} \cdot 10^{4.167}}\right)^{0.5}
$$

Calculating step by step:

1. Calculate the term inside the first parenthesis:
$$
\left(\frac{520}{14.76}\right)^{0.5} \approx 18.67
$$

2. Calculate the pressure difference squared:
$$
100^2 - 75^2 = 10000 - 5625 = 4375
$$

3. Substitute back into the equation:
$$
Q = 18.67 \cdot \left(\frac{2 \cdot 0.9524 \cdot 4375}{\pi^{0.5} \cdot 10^{4.167}}\right)^{0.5}
$$

4. Simplify the expression inside the second parenthesis:
$$
\frac{2 \cdot 0.9524 \cdot 4375}{\pi^{0.5} \cdot 10^{4.167}} \approx \frac{8357}{100.53} \approx 83.1
$$

5. Finally, calculate the flow rate:
$$
Q \approx 18.67 \cdot \sqrt{83.1} \approx 18.67 \cdot 9.12 \approx 170.4 \text{ CFD}
$$

Therefore, the flow rate of natural gas in the 10-inch steel pipe under the given conditions is approximately 170.4 cubic feet per day (CFD)

Great. Now determine the flow rate of natural gas in a 10-inch steel pipe that is 5000 feet long, with an inlet pressure of 1015 psia and an outlet pressure of 75 psia, we can use the General Flow Equation for natural gas. This equation is often derived from the Darcy-Weisbach equation and is commonly used in the industry.

The general form of the equation is:

\[ Q = \frac{C \cdot D^2 \cdot (P_1^2 - P_2^2)}{\sqrt{T} \cdot L \cdot Z \cdot \mu} \]

Where:
- \( Q \) is the flow rate (in standard cubic feet per day, scfd).
- \( C \) is a constant (approximately 1728 for the units used here).
- \( D \) is the inside diameter of the pipe (in inches).
- \( P_1 \) is the inlet pressure (psia).
- \( P_2 \) is the outlet pressure (psia).
- \( T \) is the average temperature (in Rankine, R).
- \( L \) is the length of the pipe (in feet).
- \( Z \) is the compressibility factor (dimensionless).
- \( \mu \) is the viscosity of the gas (in centipoise).

For simplicity, let's assume:
- The average temperature \( T \) is 60°F, which is 520 R.
- The compressibility factor \( Z \) is 1 (for ideal gas approximation).
- The viscosity \( \mu \) is 0.014 cp (a typical value for natural gas).

Given:
- \( D = 10 \) inches
- \( P_1 = 1015 \) psia
- \( P_2 = 75 \) psia
- \( L = 5000 \) feet
- \( T = 520 \) R
- \( Z = 1 \)
- \( \mu = 0.014 \) cp

Substitute these values into the equation:

\[ Q = \frac{1728 \cdot (10)^2 \cdot (1015^2 - 75^2)}{\sqrt{520} \cdot 5000 \cdot 1 \cdot 0.014} \]

First, calculate \( P_1^2 \) and \( P_2^2 \):

\[ P_1^2 = 1015^2 = 1030225 \]
\[ P_2^2 = 75^2 = 5625 \]

Then, calculate \( P_1^2 - P_2^2 \):

\[ P_1^2 - P_2^2 = 1030225 - 5625 = 1024600 \]

Next, calculate the numerator:

\[ \text{Numerator} = 1728 \cdot 100 \cdot 1024600 = 176701440000 \]

Now, calculate the denominator:

\[ \sqrt{520} \approx 22.8 \]
\[ \text{Denominator} = 22.8 \cdot 5000 \cdot 1 \cdot 0.014 = 1602 \]

Finally, calculate the flow rate \( Q \):

\[ Q = \frac{176701440000}{1602} \approx 110300650 \text{ scfd} \]

So, the flow rate of natural gas in the pipe is approximately **110,300,650 scfd**.

I'm gonna go get a beer now.
 
Last edited:
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I need to design a 10-inch steel pipeline that will carry 1000 PSIG of natural gas with a steel yield stress of 52,000 psi and a design factor of 0.72, you can use the design formula specified in 49 CFR § 192.105:

$$
P = \frac{2St}{D} \times F \times E \times T
$$

Where:
- \( P \) is the maximum allowable working pressure (MAWP).
- \( S \) is the specified allowable stress (yield strength), which is 52,000 psi.
- \( t \) is the thickness of the pipe.
- \( D \) is the outside diameter of the pipe, which is 10 inches.
- \( F \) is the design factor, which is 0.72.
- \( E \) is the longitudinal joint factor, typically 1 for seamless pipe.
- \( T \) is the temperature derating factor, which is 1 if the temperature is below 250°F.

Given the operating pressure is 1000 PSIG, you need to ensure the MAWP is greater than or equal to 1000 PSIG. Rearrange the formula to solve for the required thickness \( t \):

$$
t = \frac{PD}{2S \times F \times E \times T}
$$

Substitute the known values:

$$
t = \frac{1000 \text{ PSIG} \times 10 \text{ inches}}{2 \times 52,000 \text{ psi} \times 0.72 \times 1 \times 1} = \frac{10,000}{74,880} \approx 0.1336 \text{ inches}
$$

Therefore, the required thickness of the pipe should be approximately 0.1336 inches to safely carry 1000 PSIG of natural gas

However, practical pipe thicknesses are standardized and typically larger than the calculated minimum to accommodate manufacturing tolerances and safety margins. You should select a commercially available pipe thickness that meets or exceeds this requirement

Yeah, OK. What wall thickness options do I have.?

Pipe Wall Thickness Requirement

Based on the available data, for a 10-inch nominal pipe size (NPS), the commercially available wall thickness options include:

* **Schedule 40**: Wall thickness of 0.1336 inches, which meets the diameter requirement but not the wall thickness requirement you specified.
* **Schedule 60**: Wall thickness of 0.281 inches, which exceeds the minimum wall thickness you specified.
* **Schedule 80**: Wall thickness of 0.300 inches, which also exceeds the minimum wall thickness you specified.
* **Schedule 160**: Wall thickness of 0.437 inches, which also exceeds the minimum wall thickness you specified.
* **XXH (Double Extra Heavy)**: Wall thickness of 0.600 inches, which also exceeds the minimum wall thickness you specified.

Therefore, you have several options that meet your requirements, including Schedule 60, 80, 160, and XXH



Given that the adjoining pipe has a wall thickness of 0.25 inches, you should select a pipe with a similar or slightly greater wall thickness to ensure compatibility and maintain structural integrity. Here are the options that meet this requirement:

- **Schedule 80**: Wall thickness of 0.300 inches
- **Schedule 160**: Wall thickness of 0.437 inches
- **XXH (Double Extra Heavy)**: Wall thickness of 0.600 inches

**Recommendation:**
- **Schedule 80** is the closest match to the 0.25-inch wall thickness and is a good choice for maintaining consistency and ensuring compatibility.
- If you need a slightly thicker wall for additional strength or specific application requirements, **Schedule 160** or **XXH** would be suitable alternatives.

So, **Schedule 80** is likely the best option for your needs.

I need a 10" diameter pipe with a commercially available wall thickness greater than 0.1336 in thickness.

This job is too easy. I need another beer. Heck. Make it a six pack.
 
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The calculated flow rates look dodgy. Ask your AI to calculate the exit velocities as a sanity check.
 
110 Mscfd sounds like a piece of cake; the velocity must be pretty minimal, eh? Only about twice the speed of sound?
 
I think a lot of people keep forgetting that the current crop of AIs are large LANGUAGE models, and aren't really able to calculations well or, sometimes, at all
 
They'll have to walk around with their little Casios.
Why can't LLMs hand off their calculations to XL?
I checked with https://checalc.com/solved/gasPipeSizing.html
The General, or AGA equation should be used.
This pipe is too small and short to use other equations.
That gives flows 4x the 110MMSCFD above.

Velocities of short pipelines with high press drops are very high.
I was more interested in beer at the time.
 
Why can't LLMs hand off their calculations to XL?
They don't "know" when they're doing a calculation, because it's all just text that they pull out of their training set. There may be some AIs that have some sort of branching logic to get better calculations, but certainlt, Chat GPT doesn't have that. It's amusing that ChatGPT continues to crank out loads of precision that's incorrect

chat.png
 

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