AD 2000 Merkblatter vs. PED?

[adammil1]

I asked the question in another posting but really this is a second discussion so I think it deserves a separate thread. I am currently working on a project being developed for use in Germany and we need to size out the relief valves. LESER's (Germany's leading relief valve manufacturer) engineering handbook calls out sizing according to the AD 2000 Merkblatt and the methodologies are slightly different from everyone else. From what I have read in other sources my understanding is that the PED and EN/ISO codes were there to do away with all sorts of competing local regulations and allow for freeflow of goods through out Europe.

On the other hand from the AD 2000's website;

http://www.ad-2000-online.de/

This online service provides access to the complete english language versions of AD 2000 Codes of Practice on Pressure Vessels. These German Codes contain all of the essential safety requirements to be met in Germany in order to comply with the European Pressure Equipment Directive (97/23/EC) and are indispensable for implementing safety requirements in practice. With this service you have online access to the full texts of over one hundred AD 2000 Codes.

So how does the Merkblatt fit into selling things in Europe. Our company intends to go through the notified body to get a CE mark to sell in Europe but with the product going to Germany in particular is it necessary to follow the Merkblatt too or just ignore it in favor of the PED and ISO/EN standards?

 

[PaoloPemi]

for sizing PSV you should adopt ISO 4126,
results are quite similar to API codes (equivalent formulations) with some exceptions as steam where a table of values is provided for the cp/cv to utilize.

 

[don1980]

Adam - About 5-6 years ago I launched an effort to understand the current rules in Europe. I feel like I have a pretty good understanding now, but it has been much more difficult that I thought it would be. I thought I would easily find trade journal articles that concisely explained this. I never found such a publication. Instead, I’ve had to piece bits of information together from lots of different sources. It’s been very frustrating - it shouldn’t be this difficult.
PED is the legal requirement, and it doesn’t provide detailed application guidance. For that, you need one of the harmonized standards that deal with relief application. Harmonized standards are the new standards that have been developed with representation from all EU countries, and once finalized, each EU member country is required to adopt those standards as national standards. A harmonized standard (e.g. ISO 4126, EN 764-7) can be used to design relief systems which can be installed in any EU country, without that country placing additional requirement on the design. Nor can any country disallow anything that’s in a harmonized standard. Effectively, the harmonized standards are intended to replace the old country-specific standards (e.g. AD 2000 Merkblatt, Stoomwezen, etc) which were used prior to PED. By using a harmonized standard, one is granted the automatic presumption of compliance with PED. That’s not true when you use a non-harmonized standard.

A copy of the high-level PED rules can be obtained for free on their website (

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1997L0023:LATEST:EN:PDF).

Pay particular attention to Articles 1 & 2, and Annex 1.

On the PED website you can also find a list of harmonized standards. (

http://ec.europa.eu/enterprise/poli...ed-standards/pressure-equipment/index_en.htm)

Personally, I like the application standard EN 764-7. You’ll have to pay to get a copy of any of the application standards.

 

[MortenA]

well i guess that the buyer can ask for any methode as long as its in compliance with PED. So if you bid in accordance with tis requirement i think you have two options: 1) aski if you could do the design to some other standard or 2) Do the work as you told you would (unless that would be against code). As far as i know you can design accordingly to AD-2000 and be in compliance with PED.

 

[adammil1]

Asking the customer would be a start but this is actually a product being developed for a handful of different German customers in response to some laws being past in Germany but later something we really would like to sell all over the world. It is quite possible even if one customer accepts something the next may not. Really what I am looking to do is come up with a design that hopefully is good to use anywhere in the world but specifically anywhere in Germany.

It looks like I have been going through the same efforts that Don describes above and am finding it to be a challenge to say the least. I think at this point the better ones to talk with will be with our notified body who will be issuing us the CE mark as opposed to customers but we will see.

What I just can't understand is why are the Germans maintaining a set of standards the AD 2000 Merkblatt if they have been superseded by something new.

On a side note is it worth it to purchase the actual code? There are tons of great articles which I have been studying up on diligently. The latest and best that I should have started with as it appears the author has written a few of the manuals for at least LESER if not part of the Tyco manual is the "Safety Relief Valve Handbook, Design and Use of Process Safety Valves to ASME and International Codes and Standards."
They seem to be quite comprehensive themselves will the real code be worth the investment?

 

[don1980]

The design code is a key element of the documentation - it's one of the first things the Notified Body will want to see. The risk in not buying the code is that you might have some re-work due to something you didn't know. An e-copy isn't very expensive (usually about $250). If you're use ISO 4126, and plan to buy a copy, then be carefully check to see which chapters you need. They're sold separately. Before I got what I really needed, I ended up buying a couple of chapters that I didn't need.

Why do we still have national standards (e.g. AD Merkblatt, Stoomwezen) when there are pan-European standards ("harmonized standards") which can be used in any country? I don't know the answer, but I think the legecy codes probably have value from a brand name perspective. AD Merkblatt was updated to make it compliant with the PED technical requirements, but it's not a harmonized standard. That doesn't mean it can't be used. It just means that its use doesn't infer automatic PED conformity. My observation is that the transition to use of harmonized standards has been relatively slow. It's just human nature to resist change. I think there's a generational factor too. For example, I often hear older engineers in Germany and Netherlands say that pilot valve can't be used in those countries. That statement was true before PED but it's not true now. Regardless, a lot of engineers continue to follow legecy practices even though the rules have changed.

BTW, it's easy to confuse the requirements. The CE stamp is one that the manufacturer's must obtain in oder to sell products in the EU market. Most all the global manufacturers have aquired CE certification for their products. Obviously, that's especially true for those manufacturers like Leser which are based in Europe.

 

[adammil1]

Don or anyone else, I have done a little more reading on this one and I think I have a good idea of how this one all plays out especially pertaining to the sizing and selection PRVs. I was wondering what people think of my summarized thoughts here or if I am off basis?

There are 2 major laws in effect in most of the modern world. ASME Code, as well as the European PED. In order to sell an item in Europe it must conform to the PED and individual European countries must accept product for sale in them if they conform to the PED. On the other hand my understanding of the PED is that it is more of a legal document with general higher level requirements but leaves the actual implementation up to good engineering judgment and the end user. In addition to being the law the ASME code serves to aid the engineer in execution. The ASME code for example spells out how to size PRV's and run calculations. With some exceptions (for example the PED does not allow for different accumulations above release point), a user actually could use the ASME calculations, and or any other country's standard formula to size out their PRV they would just need to be careful that it fit within the PED guidelines. Indeed it would seem if my own company did the research we could create our own sound methodology to say size out a relief valve differently from other international norms as long as we could prove it safe that too would work? Would an authorized body ever sign off on such a thing?
As such since the PED does not give formulas or direction on actually calculating particular sizes etc... one must then turn to standard documents which serve more as recommendations as opposed to law. Under the category of standards one most common European recognized one is ISO 4126, but others include the old individual country code such as the Merkblatt. Providing a standard such as Merkblatt and or 4126 has been harmonized (in other words ensured to meet all higher PED requirements) the end user can actually size a valve to any standard formula of his choosing? Furthermore it is my belief that technically I could do my PED sizing using the ASME/API 520 orifice sizing calculation as opposed to the ISO 4126 if I really wanted to do so as long as met the higher PED Requirements?

Furthermore one other popular standard that is often discussed is the ASME code was deemed by the oil industry to not be specific/conservative enough so the API came out with their own recommended standard API 520 which includes recommendations harmonized to meet the ASME code.

To conclude I would say that the PED and ASME are both codes, but the ASME also contains guidelines and standards where as the PED leaves it to the cognizant engineer to choose the set of standards to follow in sizing parts. When it comes to using a standard to work towards the PED the engineer must be careful that the standard in use is harmonized with the PED.
When it actually comes to the methodology I intend to use here on our project since we are working on a product for sale in Germany I am going to see to it that we work first and foremost to the ISO 4126 while also doing our best to fit the requirements of ASME VIII at the same time, such that if our product is ever to be sold in the USA a few years later which is intended it is a smooth transition.
Is this the proper way to move forward?

 

[don1980]

Comments:

“PED is that it is more of a legal document with general higher level requirements but leaves the actual implementation up to good engineering judgment and the end user.”
[ul]
[li][/li]
[/ul]It’s true that PED is a high level legal requirement but I don’t agree with the latter part of that sentence. Applications have to be done according to an application standard, preferable a harmonized standard (e.g. ISO 4126, EN 764-7).

“The ASME code for example spells out how to size PRV's and run calculations.”
[ul]
[li][/li]
[/ul]ASME is very high level – it doesn’t spell out how to size the valve. Detailed guidance for conforming to ASME is found in the API standards. API standards are not a separate (competing) “code”. Instead, they’re complimentary to ASME – they provide practical guidance for the user in how to design relief systems which comply with ASME.

“With some exceptions (for example the PED does not allow for different accumulations above release point)....”
[ul]
[li][/li]
[/ul]Effectively, there’s no difference between PED and ASME with regard to allowable accumulation. PED states that the allowable accumulation is 10% accumulation, but in one of the PED guidelines (Guideline 5/2) it says that one is not limited to 10% accumulation in a fire case. PED says you’re not limited to 10% for fire, but curiously it doesn’t provide a specific limiting value. Consequently, a 21% accumulation limit is commonly used – same value as ASME.

“...a user actually could use the ASME (API) calculations, and or any other country's standard formula to size out their PRV they would just need to be careful that it fit within the PED guidelines.”
[ul]
[li][/li]
[/ul]ISO 4126 does have sizing formulas. EN 764-7 doesn’t have sizing formulas, but by listing ISO 4126 as a normative reference it adopts the ISO 4126 formulas.

“Indeed it would seem if my own company did the research we could create our own sound methodology to say size out a relief valve differently from other international norms as long as we could prove it safe that too would work? Would an authorized body ever sign off on such a thing?”
[ul]
[li][/li]
[/ul]I don’t think so. Refer to the comment above about formulas. You can use API 520 formulas, if they’re the same as those in ISO 4126. I can’t say whether that’s true because I haven’t compared them. But, I don’t think you can just create your own sizing methodology and say that’s in conformance with PED. I doubt that a Notified Body would sign off on that.

 

[don1980]

Adam, that formating didn't come out like I thought it would. Regardless, i think you can figure it out. I entered comments (under the bullets) to specefic statements in your post.

 

[adammil1]

Virtually everything I have read points out that the PED/ASME is the law of the land depending on where you are, while the API and EN(ISO) are "Recommendations" as Marc Hellemans puts it in his book. I guess where I struggle with in all of that is what does "Recommendation" mean?

To me it means that it is something you are encouraged to follow but not mandatory like the law. Hence my thoughts that as long as I use a normalized code such as ISO-4126, or AD 2000 Merkblatt that have been harmonized to the PED then you are all set. Since my quick read through the PED did not turn up any references to 4126, or real sizing formulas it would appear any prudent engineering calculations/design would be acceptable?

Say that one were to follow ASME/API, and never looked at the 4126, as long as they accommodated all the requirements of the PED whenever more stringent would it be acceptable for use in Europe?

Going forward I think it may be time to move on and just pick a path to run with on this project. I have a copy of the ISO-4126 on the way, we have not ordered the ASME VIII or the API 520 yet. For this project since the device is for sale in Germany I think our path forward will be to follow the ISO-4126, ignore the AD-2000 Merkblatt, and do our best with published resources to also check the sizing against the ASME/API recommendations quoted in the literature I have read through such that if the product ever does get sold in the USA we can go back and actually purchase the ASME Part VIII, and API 520 and spend the time to ensure compliance. Is this what you would do? Is there any risk to ignoring completely the Merkblatt for a product for sale in Germany if the 4126 is followed?

 

[adammil1]

One other question, the following is a Google translation of the Wikipedia page for "Druckbehälter" (Pressure Vessel), I do realize that this is a translation, and Wikipedia isn't a legally recognized source but assuming that this is correct, would it not make more sense to just use ASME and find a document where someone has also found the essential requirements of the Annex I of the PED and just design around that one design that works well world wide and ignore the ISO-4126, AD 2000 Merkblatt and all other codes/standards?

"The design and sizing of pressure vessels is described in various regulations. The Pressure Equipment Directive leaves open the choice of the applicable rules. In Germany, which is mostly AD 2000 regulations applied. There have been developed that are still used hesitant European harmonized standards for pressure vessel (standard series EN 13445). Other rules (ASME, CODAP) may also be used, if so, the essential requirements of Annex I of the PED are satisfied. The implementation of the Directive into national law was 14 by the ProdSV ( Pressure Equipment Directive implemented)."

It would be real nice to have a good one size fits PRV.

 

[don1980]

Some API manuals are labeled "standards" (e.g. API 521) and some "recommended practices". For US installations which are covered by PSM, OSHA requires users to follow RAGAGEP (recommended and generally accepted good engineering practices) and it interprets RAGAGEP as the practices found in the API manuals. So, if you're going to eventually bring this product to the US, then you'd prefer following the API sizing procedures, if that's compliant in Europe. Are API sizing procedures compliant with PED? I don't have a clear answer, but I do know that they are still very widely used in Europe. In Germany there's a very strong bias toward following AD Merkblatt, even though it's not a harmonized standard. Legally, a notified body can't deny a design that was done using a harmonized standard, like ISO 4126, rather than AD Merkblatt. If a notified body says you have to follow AD Merkblatt, then you ought to challenge them on that.

Since you have a lot at stake, I'd discuss these specific questions with a notified body. I'd use TUV since they're the dominant notified body in Germany. If they accept API sizing practices then that's an ideal solution because that means the same design can be used in Europe and in the US (compliance with API is automatically compliant with ASME).

BTW, the quote from Wiki is specifically referring to pressure vessels. EN 13445 is a harmonized standard for the mechanical design of an unfired pressure vessel. It's an EU counterpart to ASME Sec VIII, except unlike ASME Sec VIII it doesn't have a section covering overpressure protection requirements - that's left to other standards.