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Applicability of PED

Applicability of PED

Applicability of PED

(OP)
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.

RE: Applicability of PED

The PED starts from 0.5 bar g so I'm afraid it is applicable unless it falls outside of the scope in some other way.

If the fluid is a group 1 gas you are looking at category iii, if a group 2 gas or group 1 liquid then category ii, if a group 2 liquid then you are lucky and it falls within sound engineering practice.

The volume is taken between connections including all pipework, nozzles, branches, etc. (some users have interpreted it as nominal volumes but this is incorrect).

This of course assumes that the vessel itself cannot be categorised as a safety accessory in which case it will fall into category iv.

Check out the CEN forum there is a link to the directive.

RE: Applicability of PED

(OP)
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.

 

RE: Applicability of PED

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.

  

RE: Applicability of PED

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

RE: Applicability of PED

As far as I am aware the system talks of differential pressure, the fact that there is a vacuum is irrelevant.

 

RE: Applicability of PED

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.

RE: Applicability of PED

(OP)
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...

RE: Applicability of PED

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

RE: Applicability of PED

It's still open to interpretation although I accept your interpretation is valid.

I would put this to CEN for a guideline.

RE: Applicability of PED

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

RE: Applicability of PED

Unless anything is ever explicitly stated it is always open to interpretation, if I was checking a design off for this I would insist that my designers obtained clarification on the point.

RE: Applicability of PED

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.

RE: Applicability of PED

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

RE: Applicability of PED

(OP)
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.

RE: Applicability of PED

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???

RE: Applicability of PED

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.

RE: Applicability of PED

OK people, there have been some rather personal statements during this thread that are uncalled for and unprofessional, lets calm it down, if there is a disagreement or a difference in interpretation then that is all it is and different points of view should be respected.

The PED does state that a vacuum pressure is a negative pressure but that is all is states, it does not offer any other interpretation beyond that, which is why the supposition that a vacuum pressure is below the 0.5 bar is a valid interpretation but it is still a interpretation.

If there are any more derogatory remarks I will notify the web masters of this forum, I would also go so far as to suggest than some people offer an apology but I'll leave that to your discretion.

RE: Applicability of PED

Here is an answer from the guidelines that seems to support the premise that a vessel designed purely for vacuum is not a pressure vessel, it does however have additional comments that should be considered.

Quote:



Guideline 1/13
    
[Original version as adopted on: 28 Jan 1999]
Pressure equipment directive 97/23/EC
Commission's Working Group "Pressure"
Guideline related to: Article 1
Question:     Is the pressure equipment directive applicable to vacuum insulation of pressure vessels?
Answer:     Yes.

Reason: Vacuum casings which do not have a maximum allowable pressure greater than 0.5 bar are therefore not pressure equipment in their own right. However as structural elements attached to pressurised parts, they are part of pressure equipment and any negative effects of the vacuum casing and insulation on the pressurised parts must be taken into account and avoided.

RE: Applicability of PED

(OP)
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

RE: Applicability of PED

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

RE: Applicability of PED

I meant safeties. Sorry.

Regards from Barcelona
G. García

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