Pipe Design to pump sea water from the ocean to a boiler via intermediate tanks

In summary, the individual is in the process of designing a pumping/piping system for fun, with no prior experience in this field. They have been using ANSI/ASME codes and have selected a 4" nom. Schedule 40 316 SS pipe for the system. The project objective is to pump sea water from the ocean to a boiler, then transfer it to a tank for cooling, and finally pump it up a hill to another tank for drinking water purposes. They are following ASME B31.1-2001 and have chosen formula (3)' from page 16 "104.1 Straight Pipe" for minimal wall thickness. They have provided a link to the ANSI/ASME and listed the variables used in the formula
  • #1
AverageEngineer
5
2
TL;DR Summary
Trouble using formulas or overthinking...
I am in the process of designing a pumping/piping system for fun, have no experience in this field, but I enjoy learning. I have been using ANSI/ASME codes in the project quite a bit.

For the system I am using 4" nom. Schedule 40 316 SS pipe. The reason I selected the pipe is because the objective for this project is to pump sea water from the ocean to a boiler, water will transfer to a tank to cool then be pumped up a hill to another tank. The tank is suppose to provide water to the made up town of 25,000 civilians. I am only factoring in drinking water, not other uses to keep it simple.

The first leg of pipe will see a 90 degree bend. I looked in ASME B31.1-2001, (only ANSI/ASME text I could find online for free), on page 16 "104.1 Straight Pipe" it gives me two formulas for minimal wall thickness. I chose to use formula (3)' to determine min. wall thickness.

Here is the link to the ANSI/ASME https://www.nrc.gov/docs/ML0314/ML031470592.pdf

The variables are the following in the formula:
P = Design Pressure
D_o = Outer Diameter in my case 4.5" (I am using the info for the pipe here: https://titanium-stainless-steel.continentalsteel.com/item/stainless-steel-pipes/stainless-steel-pipe--type-316-schedule-40s/316-4000-4500-40s#Typical Mechanical Properties

S = Allowable stress in pipe material (PSI)
F = Joint Factor, E = 1.0 for seamless, E = 0.85 for ERW pipe
Y or y = Wall thickness coefficient in ASME B31.3 Table 304.1.1 for ferritic steel, y = 0.4
W = Weld joint strength reduction factor
A = Corrosion allowance typically 0.5

It took me awhile to figure out how to determine design pressure. I used the formula
P_design = 2 * S * t / D_outer * SF

where,
S = Material Strength (PSI)
SF = Safety Factor

My pressure at yield was 4,740 PSI and desired was 3160 PSI using SF = 1.5

On Table 102.4.5 it gives me 1.14 * t_m which gave me a radius of r = 0.745 inches with a 0.653 in wall thickness. This radius would be minimal, correct? Too me it seems like such a small radius, of course the wall thickness is quite large. What do you think?
 
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  • #2
AverageEngineer said:
Summary:: Trouble using formulas or overthinking...

I am in the process of designing a pumping/piping system for fun, have no experience in this field, but I enjoy learning. I have been using ANSI/ASME codes in the project quite a bit.

For the system I am using 4" nom. Schedule 40 316 SS pipe. The reason I selected the pipe is because the objective for this project is to pump sea water from the ocean to a boiler, water will transfer to a tank to cool then be pumped up a hill to another tank. The tank is suppose to provide water to the made up town of 25,000 civilians. I am only factoring in drinking water, not other uses to keep it simple.

The first leg of pipe will see a 90 degree bend. I looked in ASME B31.1-2001, (only ANSI/ASME text I could find online for free), on page 16 "104.1 Straight Pipe" it gives me two formulas for minimal wall thickness. I chose to use formula (3)' to determine min. wall thickness.

Here is the link to the ANSI/ASME https://www.nrc.gov/docs/ML0314/ML031470592.pdf

The variables are the following in the formula:
P = Design Pressure
D_o = Outer Diameter in my case 4.5" (I am using the info for the pipe here: https://titanium-stainless-steel.continentalsteel.com/item/stainless-steel-pipes/stainless-steel-pipe--type-316-schedule-40s/316-4000-4500-40s#Typical Mechanical Properties

S = Allowable stress in pipe material (PSI)
F = Joint Factor, E = 1.0 for seamless, E = 0.85 for ERW pipe
Y or y = Wall thickness coefficient in ASME B31.3 Table 304.1.1 for ferritic steel, y = 0.4
W = Weld joint strength reduction factor
A = Corrosion allowance typically 0.5

It took me awhile to figure out how to determine design pressure. I used the formula
P_design = 2 * S * t / D_outer * SF

where,
S = Material Strength (PSI)
SF = Safety Factor

My pressure at yield was 4,740 PSI and desired was 3160 PSI using SF = 1.5

On Table 102.4.5 it gives me 1.14 * t_m which gave me a radius of r = 0.745 inches with a 0.653 in wall thickness. This radius would be minimal, correct? Too me it seems like such a small radius, of course the wall thickness is quite large. What do you think?
You either misused table 102.4.5 or miscalculated t_m.
1.14 is additional thickness multiplier to t_m.

For your case, t_m/Douter=Pdesign*SF/(2*S)~(0.04-0.06)
 
  • #3
Okay... Where does the equation come from?
 
  • #4
AverageEngineer said:
Okay... Where does the equation come from?
It is transformed equation from your source.
 
  • #5
Not an expert on piping design, but I've seen very high safety factors for stainless steel pipe. Safety factors in the order of 8 to 12. Not sure why so high though, but if i compare that against 1.5 then i have to wonder if that's maybe too low.
 

1. What factors should be considered when designing a pipe system to pump sea water?

When designing a pipe system to pump sea water, factors such as the flow rate, pressure, pipe material, corrosion resistance, and maintenance requirements should be taken into account. The distance between the ocean and the boiler, as well as any elevation changes along the way, should also be considered.

2. How do you determine the appropriate pipe size for the system?

The appropriate pipe size for the system can be determined by considering the flow rate and pressure requirements. A larger pipe diameter will allow for a higher flow rate, but may also increase the cost and energy consumption. A smaller pipe diameter may result in higher pressure losses and require more pumping power. It is important to strike a balance between these factors when selecting the pipe size.

3. What type of pump is best suited for pumping sea water?

Centrifugal pumps are commonly used for pumping sea water due to their ability to handle high flow rates and low to medium pressures. However, for longer distances and higher pressures, positive displacement pumps may be more suitable. It is important to consider the specific requirements of the system when selecting the type of pump.

4. How can corrosion be prevented in a pipe system carrying sea water?

Corrosion can be prevented by selecting the appropriate pipe material, such as stainless steel or corrosion-resistant alloys. Additionally, regular maintenance and monitoring of the system can help identify and address any potential corrosion issues. Coatings and cathodic protection can also be applied to the pipes to prevent corrosion.

5. What is the purpose of intermediate tanks in this type of pipe system?

Intermediate tanks are used to regulate the flow of sea water and maintain a consistent pressure in the system. They also serve as a buffer, allowing for changes in demand and preventing any sudden pressure surges or drops. The tanks also provide a place for any sediment or debris to settle before the water is pumped into the boiler.

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