Applicability of PED 1

[teokal]

Dear all,
we had a conversation at the office, about the following matter: Our (pressure) vessel is a vacuum separator, with operating pressure vacuum, and design pressure -1 bar(g). The capacity is 0,36 cubic meters (360 litres). Design and operating temperature is 100 degrees celcius. According to my knowledge and opinion, and as I have read the PED, the directive is not applicable on this vessel. Other colleagues though, have different opinion. Please advise.

 

[teokal]

Dear Fawkes,
maybe you did not understand; the design pressure is -1 bar(g) (minus one bar). So it should not be inside the scope of PED. This is my belief, also.

 

[DSB123]

teokal,
As you point out Fawkes is incorrect. If the Design pressure is less than 0.5 Bar G then your vessel falls outside the scope of the PED. It's all in the (minus) sign.

 

[gr2vessels]

Guys,
Please review the pressure vessel code of any country in this world, the minus mentioned means full vacuum, which will place the vessel under the BPVC jurisdiction (ASME VIII, EN 13445, PD5500, etc...), including PED.
cheers,
gr2vessels

 

[DSB123]

gr2vessels/Fawkes,
If you are suggesting that a pressure vessel subject to full vacuum falls under the PED then can you advise how you would categorise a unit with say 20 Cubic metre volume and a pressure of Full Vac. I don't thionk you would be able to enter any of the categorisation graphs for either Fluid type 1 or 2 as these cover positive pressure values ONLY with a lower limit of +0.5 BarG.
I agree that a full vac vessel falls under the applicable Pressure vessel Code but not PED. Please prove otherwise.

 

[teokal]

PED, Guideline 8/7, Note 3:
"pressure related to atmospheric pressure", as defined in Article 1 paragraph 2.2, is the pressure inside the envelope. It shall not be interpreted as "differentialpressure between atmospheric pressure and absolute pressure prevailing inside the equipment" for the purposes of classification.
To finish this, pressure vessels designed to work at vacuum (-1 bar (negative pressure)), ARE NOT included in PED's scope.
Thank you all, guys...

 

[DSB123]

teokal,
Spot on!! Exactly what I was saying. No more to be said really.

 

[DSB123]

Fawkes,
There is no interpretation needed. Full vac (-1 Barg) is less than 0.5 Barg - end of story!!!

 

[DSB123]

Fawkes,
The PED is explicitly clear - no interpretation is needed. If the pressure is not above 0.5 Bar then it's not within the PED. If you are not clear of the PED concept's then perhaps checking should be performed by personnel whom are conversant with the PED.

 

[gr2vessels]

DSB123,
Full vac Is more (not less) than 0.5 barg. Try to put these figures in a calculation formula for shell thickness, to see which yields higher thickness. That is the end of the story.
I don't argue on the PED issue, but please note that the Scuba divers oxygen tank, designed for full vacuum is explicitly included in PED's scope. So how is this separator classified if it is operating in lethal service, remains to be seen.
Cheers,
gr2vessels

 

[teokal]

gr2vessels,
don't forget that the scuba divers oxygen tanks are designed to operate for a pressure of + (plus) 180 to 200 barg (I can't recall exactly their operating pressure) AND full vacuum - this is another story. Also, breathing equipment is included to PED mostly because it is considered as Personal Protective Equipment, and they can not be categorized somewhere else, since TPED (Trasportable PED) excludes gas cylinders for breathing appliances (Recital 9 and Article 2, section 1).
In order to get into a classification for the PED, you have to calculate this: Ps * V. With negative Ps (Ps cannot be absolute) you have negative produvt of the multiplication, and therefore you can not "enter" into any of the tables of Annex II.
Also gr2vessels, calculation formula for shell thickness is one thing; PED is another; ASME VIII (for exaple) is a calculation and construction coe, PED is a LAW.

 

[DSB123]

gr2vessels,
Thanks for the lesson but I always thought a positive number was greater than a negative number. Obviously that's not the case. In any event the question was about the applicability of the PED to a vessel under full vacuum. So why change the story???

 

[DSB123]

gr2vessels,
Not wanting to be pedantic but the original question was about the applicability of the PED not design thickness calculations. Also scuba divers tanks are normally pressurised to well over +0.5 Bar (that's why they fall under the PED) and although they have a full vac design case I very much doubt whether a scuba diver would last too long if his tanks were under vacuum when he was diving.
The PED is all about stored energy and its danger to the public - read it and this is evident. A vessel under full vacuum will implode if it fails not explode.

 

[teokal]

Dear all,
when I was starting this thread, I couldn't imagine that some of us would be offended... The same spirit of arguement though was present in my office with my colleagues, while applying "brainstorm" for this matter... So, technically, I remain to my statement and belief that P.V. under vacuum and designe pressure -1 (minus one) barg are not included in PED's scope (I'm not talking for e.g. 14,5 barg/F.V. - they are another story), but anyway I will forward this question to the European Community, in order to have some official answer and hopefully a new - and clear - guideline.
P.S. Just for the record, the score up to now (taking into account 43 engineers' opinions from 15 different countries from 2 continents) is:
not in PED scope - 38
yes in PED scope - 5
Thank you all, people

 

[ggarciae]

My vote is not too.
Never ever in Spain a vacuum vessel has been considered a pressure vessel.
Vacuum is considered in design and securities, but not in the legalizations.
Regards

Regards from Barcelona
G. García

 

[ggarciae]

I meant safeties. Sorry.

Regards from Barcelona
G. García