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High Pressure Piping Design, B31.3, start at 2500 psi?

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eagle1900

Mechanical
Sep 11, 2006
25
I try to understand if we can determined if we design an high pressure system when the pumps before the piping push at 3500 psig?

Has it a value to determined when it's a High Pressure Piping Design, like specify in the B31.3, Chapter IX? When the owner doesn't know...

Is high pressure at 2 500 psig? 5 000 psig, 10 000 psig?

many thanks for your help!

Mechanical Engineer
 
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Owner abdicated? It is then encumbent on the Engineer-of-Record for the piping system to declare it. Me, I would use most, if not all of the B31.3 High-Pressure design & testing criteria at 2500 psig, and formally declare the system to be High-Pressure [making the B31.3 'extras' mandatory] at 4000 psig. Just write up two different Line Spec's. One for 2500# max, with your design & NDT expectations. One for "High-Pressure" starting at 4000 psi, and mention that the B31.3 'extras' are mandatory.

Did that a year or more ago [2500# and 100% RT/UT, etc], everything is running well.
 
So what I understand is I'm between a "normal" pressure and the High Pressure...

The problem I have with that is I want to modify a little manifold bloc valve. The owner doesn't want to weld a piece of pipe (diameter 1 inch). So I saw in the Chapter IX the specification for using thread and what I found is I couldn't make NPT thread to connect my pipe. I should use something like "Swagelok", but I don't find how to make a good thread in a Stainless Steel (SS) bloc because that become not standard...

Any suggestions about how to make a good assembly with thread in a bloc of SS ?

Is only welding assembly respecting the B31.3 in my case?

Mechanical Engineer
 
2500# class, not 2500 psig unless the temperature is also very high.
 
Now you see why I don't delare "High Pressure" at 2500# / Class 2500. It gets VERY restrictive. If you keep your category at "Normal Fluid Service", you can use one of the propriatary high-pressure threads, like the cone threads from Hy-lok:


To 'cover' yourself for audits, etc. write a Line Spec that puts all the foregoing on paper, to include Corrosion Allowances. Then follow that Spec, as it is now your "Written Practice".
 
Thanks Duwe6,
Where did you find "High-Pressure" start at 4000 psi? In the B31.3 ?


Thanks Moltenmetal,
In my case I'm at ambiant temperature and my fluid is water...

Mechanical Engineer
 
moltenmetal ,

Thanks I see I'm at higher than class 2500. Do you know a reference showing how to determine the class?

Mechanical Engineer
 
If you will look at B16.5, you find out that past Class 2500 "you're on your own". Calc out and draft a Line Spec that adequatly covers your operating & design conditions.

As for the 4000#, it is one of my "rules of thumb". B31.3 expects the Owner or Piping Engineer to decide where to declare "High Pressure". Since I can buy off-the-shelf flanges for Class 2500 pressure & temperature, and Sch 160 or XXS [do the calc's and leave a Corrosion Allopwance] work, I don't go to the full-blown High Pressure rules until about 4000# design pressure.
 
Refer to ASME B31.3 Section K300 (a) "High pressure is considered herein to be pressure in excess of that allowed by the ASME B16.5 Class 2500# rating..."

 
that'S good Duwe6, I get the same way of mind than you after few verifications. That confirm me its better to use welding fitting or to weld a flange on the casing than using thread like High Pressure rules...

I don't want to imagine how hard it could be to find parts for a 10 000pisg system because for 3500psig it was pretty cool ;)

Thanks guys!

Mechanical Engineer
 
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