PCC-2 2022 Pneumatic Testing Safe Distance Calculations

[NamiTS]

Hi All,

In the new 2022 edition of PCC-2 when calculating the safe distance for pneumatic testing PCC-2 states that for a the stored energy calculation "the total volume of the vessel shall be considered. When calculating the stored energy of a piping system the maximum volume based on a length of 8 pipe diameters may be considered for any single failure analyzed." I understand why the differentiation exists due to the different types of rupture mechanics between piping and vessels, and have read the associated paper from what this is based on.

My question stems from the wording "for any single failure analyzed" and if this volume limitation would apply when completing calculations for a system. For example a small vessel with multiple piping systems. For the spreadsheet I made to do the stored energy calcs I have included the entire volume of the pressure vessel + the volume of largest line connected in the test using a maximum length of 8*d of pipe.

In my opinion this would be conservative but I wanted to see if this wording was disallowing this calculation and if other people are including all of the piping volume for their system calculations.

 

[GD2]

I am not sure if the clause of 8D pipe length had been brought to uniform the extra volume we used to add to take care of the volume in the test header, and the connecting hoses.

I used to add this volume as 10% of the actual calculated volume of the piping system.

My other interpretation will be, when deciding on how much the piping length should be included in the test system, it shouldn't be more than 8D length. Perhaps, it is meant to limit the stored energy and the safe distance. Again, I believe this clause is applicable to only testing a piping system without a pressure vessel.

GDD
Canada

 

[NamiTS]

Hey GD2, I was trying to understand where it came from and eventually ended up buying the paper that PCC-2 references. To roughly summarize the paper:

"If the final rupture opening area is larger than the critical opening area A* (i.e., two times the pipe cross-sectional area), the use of the standard PVB blast curves with a four-diameter effective volume was found to provide a reasonable bound to the test data for a pipe rupture at grade level with the high pressure gas jetting upwards. For the purposes of blast load predictions for safety analyses, it is recommended that this volume be doubled (i.e., to 8 diameters) to address variation in parameters and to provide a degree of margin."

I believe it is to limit the safe distance and stored energy due to the nature of pipe ruptures and how much fluid can react during the initial event. Following that logic I would assume that it would carry over into full system calcs as the stored energy in multiple pipes would not contribute heavily during the rupture of another on the system as you would still be subjected to the speed of sound*10 ms. Depending on rupture location you could have some slight interaction but I would think that would be captured with including the entire pressure vessel volume. In the scenario the pressure vessel ruptures there could be a larger degree of interaction but I would think including the pipe volume base on an effective length of 8*d would also capture that.

My worry is that when using the actual volume of pipe it drastically increases the stored energy of the system and in turn requires a illogical safe distance to be maintained.

I'm not super familiar with this though so please let me know if I'm thinking about this in the wrong way.

 

[r6155]

ASME PCC-2 is up for repair.
Can you explain what the repair is?

Regards

 

[NamiTS]

Hey r6155, this is just going to be an attachment for an internal procedure no specific repair.

 

[GD2]

NamTs,

Is the paragraph you quoted from 2022 edition, for blast load analysis or actual volume calculation?

Is it possible to send the entire paragraphs? I don't have the 2022 edition.

GDD
Canada

 

[NamiTS]

GD2,

It is located twice once in para 501-6.2(e) Pneumatic Pressure Test of Pressure Vessels or Piping which states:

The maximum calculated stored energy of any vessel or piping system being pneumatically pressure tested should not be greater than 271 000 000 J (200,000,000 ft-Ib). When calculating the stored energy for a vessel, the total volume shall be considered. When calculating the stored energy of a piping system, a maximum volume based on a length of 8 pipe diameters may be considered for any single failure analyzed.

It is also located in Mandatory Appendix 501-II Stored Energy Calculations for Pneumatic Pressure Test:

When calculating the stored energy for a vessel, the total volume shall be considered. When calculating the stored energy of a piping system, a maximum volume based on a length of of 8 pipe diameters may be considered for any single failure analyzed.

 

[GD2]

NamiTs,
---When calculating the stored energy of a piping system, a maximum volume based on a length of 8 pipe diameters may be considered for any single failure analyzed. - Does it mean that in case there is a failure, this is the volume to applied to analyse the failure event?

i guess as long as we don't exceed the limiting stores energy, we should be fine to calculate and test a piping system with volume that don't exceed the limiting stored energy.

GDD
Canada

 

[tranduyquang]

May I have advice for the calculation for piping system which spreads on few decks, should we use the 8*D for the formula for the whole system? Or we can split piping by decks, and use 8*D for each decks into the calculation (note that piping run continues from deck to deck, no isolation).
For example: Piping has 30m of 10" on top deck, then 20m of 6" on the main deck. What should we determine for the safety distance? Thanks

 

[GD2]

Tranduquang,
Until more interpretations and clarifications comes out of the 2022 Edition, I would follow the old rule to be safe.

GDD
Canada

 

[tranduyquang]

@GD2
Could you advise me with the old rule? Which formula should we use? Thanks!

 

[GD2]

Tranduquang,

It's the same formulas. Instead of using 8D test volume for the piping, consider the total volume of the test system and follow the calculation for stored energy/TNT and safe distance.

GDD
Canada