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May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Im struggling with an issue here to which the applicable Code(s)/standards dont really seem to provide an answer, I think.

Our company (EU-based) quite often produces it's own SEP (Sound Engineering Practice) vessels, which are small vessels that fall under the regulations of the PED (97/23/EC), article 3 paragraph 3.

For those unfamiliar with the PED, these kind of vessels have to be produced acc. article 3 paragraph 3 of the PED (PRessure Equipment Directive), which basically tells you one needs to produce such a vessel according to good craftsmanship.
You dont e.g. need PQR's/WPS's, WPQ's, calculations, etc. for vessels which fall into this category. Examples of SEP vessels are pressure vessels for which the vapour pressure at highest temperature is higher than PS = 0.5 bar above normal atmospheric pressure, but with the limitation that for fluids in Group1 with a volume greater than 1 L and a product of PS and V greater than 25 bar·L, or with a pressure PS greater than 200 bar (Annex II, table 1).
Parallel to this, there are more groups (and limitations), but just to give an idea.

Now, if I make pressure vessel for hydrogen (say 200 bar, 0.5 Ltr), to which the above mentioned rules apply, I might want to do some calcs for the wall thickness. You dont want to have such a vessel exploding, even though (acc. to PED) you dont need to do any calcs.

To make things simple, I thought it might be a good idea to do the calcs acc. to a simple yet effective code for pressure containing equipment.

Since most of these SEP vessels are produced with a lot of piping components, I thought of using B31.3. Im starting to get familiar with this code, and it would take me too much time to go through BPVC Sect VIII Div 1 thoroughly.

My question now is, if it's allowed to use ASME B31.3 as the design code for such a pressure vessel. The components of such pressure vessels are often a piece of pipe/tube, which a cap (or sometimes a tubing flange), and some half coupling branches on the side.
I looked through B31.3 but I couldnt really find a section which made it clear I couldnt use this Code for such a design.

Another example is a tube in tube heat exchanger, also made of 2 pieces of tube, perhaps a Tee at the end for in- and outgoing fluids, and a cap to close the tube headers.

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

No problem, PED accepts B31.3 as a good design code.

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Have tried searching the PED to see where it states you do not need PQRs, WPSs or welder quals for SEP and cannot find a thing.

3.1.2. Permanent joining

For pressure equipment, permanent joining of components which contribute to the pressure resistance of equipment and components which are directly attached to them must be carried out by suitably qualified personnel according to suitable operating procedures.
For pressure equipment in categories II, III and IV, operating procedures and personnel must be approved by a competent third party which, at the manufacturer's discretion, may be:......

How can welding pressure vessels irrespective of pressure without a weld procedure or qualified welder be considered "Sound Engineering Practice".?

What is the official definition of "Sound Engineering Practice" ?
There really isn't one - the PED states "what is recognised as Sound Engineering Practice in a Member State" so SEP in Britain may be a lot more stringent than SEP in one of the lesser member countries (or states) in the EU.

Best explanation I can find for SEP is in the Simple Pressure Vessels Directive.

Directive 87/404/EEC, the Simple Pressure Vessels Directive

Safety requirements for category 'B' vessels

Vessels in Category B are subject to much less complex requirements than those in Category A and do not require Notified Body involvement. Instead they must be manufactured in accordance with "engineering practice recognised as sound in an EEA state". In practice, this means that the ASME codes or the former BS 5500 could be used, or any EU member state's pressure vessel code from before harmonisation under the Pressure Equipment Directive.

Your thoughts ?

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Hi Kiwi2671,

You're absolutely right, with respect to part 3.1.2 you reffered to. It is true you need qualified people to do the welding on a pressure vessel, even if the vessel has a design pressure which e.g. is 0.51 bar above atmospherical/environmental pressure (i.e. it's just within the scope of the PED).

However, my explanation (see first post) was more referring to the fact that the PED, for art 3 para 3 type of vessels ('SEP' vessels) doesnt require you to document calculations, produce a manufacturers data book (containing the PQR's/WPQ's/WPS's etc) with a welder's log, etc.
What we usually do for such a SEP vessel is make a calculation, but dont produce a complete manufacturings book with the calculations, welder's log, and PQR's/WPQ's, all EN 10204 3.1 certificates, etc.

Second, you can imagine that e.g. when you want to make a 20 bar 0.5 Ltr condensate vessel (which is a SEP vessel) with a design temperature of 120 deg C, and use a 1/2" Sch 40 pipe, with caps at the end, and 3 or 4 Swagelok weld-on connectors, you for a fact now the vessel is strong enough to withstand the pressure at design conditions. You dont need to do a complete calculation for that.

However, your post has opened new light to the case for me; Ill review the current way we produce the vessels and see at which points we might do some improvements, if required per PED, or if it improves the quality.

Furthermore, if there really isnt an explanation of SEP, there really isnt anything/anyone to tell you when you meet the SEP requirements, hence it's up to your own quality practice, to define when something is SEP, right?

Kiwi, do you agree with europipe you can do a calculation for the vessel's strength, you may use the rules of B31.3 for the complete design of the vessel (i.e. design for wall thickness etc.)?

PS: it's nice you brought up the SPVD, however, for vessels under PED it doesnt really apply, right?  

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

By the way guys, thanks for the responses so far (couldnt edit my last post)

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Kiwi, i looked into the PED again, and noticed that you're wrong on your first point; para 3.1.2. falls under essential safety
requirements, and the essential safety requirements are no part of SEP. So for a SEP vessel, you dont need PQR/WPQ etc per PED.  

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

I agree with what you are saying and I agree the WPS, PQRs and welder qualifications do not need to be submitted in an MDR.
My point was how can you weld a pressure vessel (regardless of the pressure) without a welding procedure and without a qualified welder and call it Sound Engineering Practice ?

"You dont e.g. need PQR's/WPS's, WPQ's, calculations, etc. for vessels which fall into this category"

I was simply responding to this statement in your first post,

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Hi kiwi, that's exactly what I meant. You dont, per PED requirements, need them, but of course you'll make a vessel using (previously qualified) certificates etc. But thats not my point of discussion right now, what Im after is a discussion regarding my original/initial thread topic, namely if one may produce a SEP (PED art. 3, para 3) vessel following the rules for (pipe) wall thickness of B31.3 rules?

Im aware the PED exists (europipe, thanks for you answer), Ive read it before, but now Im struggling with this question ...

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

PED doesn't proscribe the way you calculate the vessel, as long as the design calculations are okee.
B31.3 is excellent for PED.

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Hi europipe,

thanks for your asnwer, I was also thinking the first ('PED doesnt subscribe any design code'), I however was unsure about using  a piping code for the design of vessels.

do you have experience with this, europipe? or do you know from industries' practice this is (readily) accepted (i.e. using piping codes for design of vessels)?

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

You are talking about a SEP vessel,
so there is no need for consulting a NOBO.
When the calcs are okee there is no further action required.
Look at the link I sent, check the modules you need.

RE: May a SEP (PED art. 3, para 3) vessel be designed acc to B31.3 rules?

Hi europipe, im not 100% familair with the PED (yet), but I'm familiar enough with the PED to be aware of the modules, NOBO involvement etc.

My question wasnt really related to whether or not the PED accepts B31.3 for the design of SEP vessels, but my question was (originally) aimed to find out if its good engineering practice (or industry practice, if you want) to use a piping code for the design of SEP vessel (regardsless of the PED requirements, which, as you mentioned, doesnt disallow the piping code for design of SEP vessels).

thanks again for your answers.

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