BASIC QUESTIONS FROM A BEGINNER 1

[RANMAN3]

I'm learning pipline design in my spare time. Can you guys answer a few questions to prod me along. I intend to be an expert someday using API 620.
1) What does the stall head tell me about static pressure. I know its potential energy balanced by potential energy. The problem is that in Bernoilis equation I need a static pressure to calculate forces, not the momentum equation, but just the pressure times area. What will the initial static pressure at the outlet be?
2) How do I determine the flange class for the system? I just cant see the flange load without a change in momentum or static pressure change across a flanged joint of constant area pipe. Is it just longitude force due to internal pressure? It cant be that easy.
3) If I need to calculate reaction forces at an elbow, I need static pressure. Do I calculate the pressure drop up to that location and subtract it from the pump outlet static pressure? I know I can find momentum from change in velocity in xy coordinates.
4) What is the best typ of pump for water?
5) What is a good value for corrosion allowance for indoor piping say 100F?

Randy

 

[BigInch]

Initial static pressure at the outlet to atmosphere is 14.7 psia. If the water above has an equal (the water column is 33.92 ft high with a vacuum on top), pressure downwards=14.7 psig and it won't move.

Flange class is based on pressure in the system.
For example, ANSI#600 will suffice for an internal pressure of up to 1460 psig (at room temperature).
ANSI#300 is up to 720 psig internal pressure.
The flange bolts must hold a load = pressure x cross-sectional area.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[RANMAN3]

Thanks for the info on class. Is the area the fluid area? How does static pressure get s high?
If I have a column of fluid at H, I can calculate P at bottm by gamma*H, or the velocity by H = C*V^2. But in Bernoili, I need both static and velocity head. How do I proprtion the two at the pump outlet so I have point 1 of Bernoilis.
Randy

 

[BigInch]

Ignore velocity head. It's usually pretty small. Once you know your pipe size, you can go back and calculate v head.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[MikeHalloran]

<disclaimer: no knowledge claimed re API stuff>
Re flange bolt load:
There's always some moment load on a flange, rarely accounted for in calculations except by factor of ignorance.
The separating force is the product of the contained fluid pressure and the area over which the pressure acts. Using the pipe bore or even the gasket ID is not conservative, because it assumes that the gasket seals completely at its ID. Better to use the OD of the raised flange area, because as the gasket starts to leak, the fluid pressure reaches a greater extent of the flange face.
<aside>
I have seen o-ring sealed hydraulic valves, finely made, where after the o-ring started to leak, the effective area became the OD of the land around the outside of the o-ring face seal groove. The subject came up because the ends were not flanged, but equipped with a (too-thin) internally threaded union nut, which yielded enough to slip by one full thread, after which oil sprayed everywhere. The safety wire on the nut stretched, but held well enough to keep the nut from unscrewing completely. Beware high pressures.
</aside>

Mike Halloran
Pembroke Pines, FL, USA