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

[eagle1900]

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

 

[Duwe6]

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.

 

[eagle1900]

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

 

[moltenmetal]

2500# class, not 2500 psig unless the temperature is also very high.

 

[Duwe6]

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:

http://www.hylokusa.com/products/fittings/high-pressure-fittings.aspx

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".

 

[eagle1900]

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]

It's not AT 2500# class, it's BEYOND 2500# class.

 

[eagle1900]

moltenmetal ,

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

Mechanical Engineer

 

[Duwe6]

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.

 

[stanweld]

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..."

 

[eagle1900]

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