DIN Standard Flanges vs ASME Flange Ratings 2

[RPRad]

I am sure this must have been asked numerous times before, but I couldnt find a thread that clarified. I have been asked to look at piping system (constructed to B31.3) that includes several several DIN Flanges (ie presumably utilized to tie into DIN flanged process control valves and process equipment)...The SRV used to protect the system is also DIN standard which is a bit odd.

It is well known that DIN standard flanges for a given pressure rating are dimensionally smaller than a similarly ANSI/ASME rated flange. Is there a chart out there that indicates what the equivalent DIN Standard Flange would have to be used to satisfy ASME (for the standard ratings Ie 150#, 300# etc). It is likely if there is no recognized equivalency that the boiler inspector will request that the DIN Flange be evaluated with respect to ASME Section VIII, Div 1 Appendix 2 in which case they likely will be undersized for the design pressure conditions not too mention the material equivalency issue. Is there any precedent or recognition under the code to deal with this, I know there have been efforts made to try and standardize between North America and Europe...but I dont think there is anything formal in place as yet.

Any solutions to this issue? Or should I just design some DIN geometry flanges (ie bolt circle etc) under Appendix 2 and attempt to qualify the valves or process equipment via a hydrostatic pressure test (although the latter raises some issues). Also can a DIN standard SRV be used in an ASME piping system?

R

 

[XL83NL]

DIN flanges have been superseded by EN 1092-1. Maybe your system is so old you have true DIN flanges, but DIN is like ANSI: it used to be called that way way back, but then they changes it to EN, resp. ASME, nowadays.
EN (or DIN if you want) flanges can be used under B31.3, I think, as youre using a code/standard that may satisfy the requirements of 304.7.2. Same counts for EN materials, although their design basis is different to ASME (other safety factors, design limits and approaches), which may require a bit more digging.

Im not sure about the chart you're after. Can you elaborate a bit more on what you exactly look for?
Do you need to know what PN class corresponds to pound class? For that purpose, Google may well assist you.
Hope this helps you a bit further.

 

[RPRad]

Heard of EN-1092, yes I havnt physically looked at the flanges to see what the actual markings are as yet, the piping contractor has spec'd them as DIN, probably DN is what they are actually marked.

I guess quite simply what I am asking is if the flanges he has identified as being European are marked rated for the line conditions can they be used at those conditions?. Because I know the boiler inspector is going to notice how much thinner they are than the ASME flanges (especially with both present on the line) and ask me to prove they are acceptable for the pressure conditions specified.

So in summary, I believe what your saying is that while the EN standard defines the flange specifications and therefore makes them acceptable for use under the Code (satisfying the Quality Assurance side of things), it may not make it acceptable for use under B31.3 at its marked pressure rating because of differences in the design methods, which is where my concern lies. Which is why i was wondering whether if some industrious person had come up with a max pressure rating for these flanges with respect to ASME or if you are basically forced to do an Appendix 2 calc and see if you meet the flange thickness requirements for the line conditions?

 

[LittleInch]

I'm not sure that you've actually grasped yet the different system of flanges here. EN flanges are designated by pressure class (PN) and size (DN). DN is not short for DIN, but in metric units is the same as ND for ASME pipe and fittings. Hence DN 150 is directly equivalent to 6" pipe.

PN on the other hand is max pressure rating in barg. This goes in the sets 2.5, 6,10,16,25,40,64,100. If these are lower than an ASME B16.5 flange, then this, or indeed any other lower rated pipe or fitting is what determines the pressure rating of the system or pipe. The fact that there is a flange capable of higher rating is irrelevant. The flanges should be stamped with the PN rating.

E.g, you have a # 150 flange at ambient temp on a line which has a PN 10 flange. This (the PN10 flange) is the lowest rated bit of kit on that line. The PN 10 flange therefore limits the pressure rating of that line to 10 bar, not the 19 bar that the #150 flange could stand. Look for the line list which will specify the design pressure for that line and ensure that the PN rated flange is the same or higher than the design pressure.

Because there are lower rated EN flanges than #150, you may not be comparing similar rated flanges, but as you say, they can be acceptable "for the pressure conditions specified". You haven't told us any details so it is difficult to judge whether the design has actually considered the PN rating properly or not.

You need to forget this search for equivalent. The two systems are different so won't be equivalent. Get over it and check that the rating is good enough for your pressure conditions. This is no different from checking that a wholly ASME system rated for 40 bar doesn't contain any #150 flanges. The fact that the class 300 flanges can handle more than that is not necessarily the "pressure rating" of your system.

So, find your pressure rating and then check that any piece of kit on that system meets or exceeds the design pressure and then you can show the inspector, the pressure rating is, e.g.12 bar. This strange looking flange her is PN 16 flange which has a pressure rating of 16 bar and therefore is OK. Substitute in any pressure rating, in bar to make it easier, and away you go.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[RPRad]

I understand exactly what the DN and PN numbers stand for and the difference with regard to DIN (although in the past you could end up with DIN standard flanges on some German supplied piping and pressure equipment...probably dating myself with that one) . The problem is not all North American jurisdictions accept the pressure ratings marked on European flanges, principally this is because the way they are designed they can end up being notably thinner than a B16.5 flange for the same approximate pressure rating (i.e., this is simply due to the difference in the way European flanges and ASME flanges are designed...and this thickness difference is what typically freaks out the AI).

Thus the jurisdiction will commonly require me to prove equivalency to ASME (which includes from a QC point of view, from a material point of view and design calculation point of view.....doesnt matter whether its European, Chinese etc), I am not saying its right that they ask that but its common request. The QC issue isnt too big an issue if its been designed to a country standard and the flange is properly marked and dimensioned, crossing the material across to an equivalent ASME material is generally not to difficult either, the issue comes when you try and use ASME allowable stresses and design formulas you generally end up with a thicker flange for a given pressure rating. If your system design pressure is low you can generally get them by, but if the system pressure is closer to the flange rating then you can have a problem. So what I am saying is that a PN6 flange may not be thick enough (under ASME) for for a line with a design pressure at or close to 6 Bar, so to satisfy ASME the European flange may have to be PN10.

So my problem is not that I dont understand the rating system, my problem is that when the jurisdiction doesnt recognize the European rating system and they want proof of equivalency under ASME (ie lets say I have a PN6 flange in the system and the design pressure of the system is 5 Bar, they will not accept the 6 Bar rating and go away, instead they make me prove that the PN6 flange thickness is acceptable for a design pressure of 5 Bar using ASME design rules). I am not saying that I agree with the jurisdiction on this or that I personally have issue with European designed flanges, but I am not going to win an argument with them by saying that if they are acceptable for use in Europe at that pressure rating then they should be acceptable for use in the North America on a system at or below that pressure rating. So basically what I was looking for was an equivalency table indicating the maximum pressure rating for a given European flange using ASME design rules...doesnt sound like such an animal exists so I will likely just end up doing the calc to find out which PN has a flange thickness acceptable to ASME for the given line design conditions

 

[RPRad]

I should add that I do see the irony in the fact that even ASME standard B16.5 flanges will not always meet the thickness requirements for a given pressure rating when subject to ASME calculation

 

[LittleInch]

Thanks for the further explaination and please accept my apologies if I came accross as lecturing or being simplistic, but there are lots of posts here which need that sort of explaination.


Hence what I now gather the issues are is that essentially your inspection jurisdiction is wary of the EN flanges and essentially under B 31.3 section 304.7.2.a) doesn't accept them as having
"(a) extensive, successful service experience under
comparable conditions with similarly proportioned
components of the same or like material."

Hence although this is effectively Plan A, you are looking for a plan B which is calcualtions undertaken to ASME VIII Div 1 appendix 2 for EN 1092 flanges to establish their max working pressure based on ASME VIII methodology and figures, which is likley to be less than their designated rating due to the different design methods used in the two codes.

So perhaps the real question is " Is there some general guidance / ruling from a higher authority than your local jursidiction which allows the use fo EN 1092 flanges without needing to certify them against ASME VIII rules?". If there is you can then wave that in front of the AI and however reluctantly, this should solve your problems. I don't know but others here might.

Good luck and apologies again if I insulted your undoubted intelligence and knoweldge on this item.


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[XL83NL]

Not so long ago I faced the problem of having to use inconel 625 flanges acc. EN standard.
As B16.5 recognizes Inconel 625 flanges under group 3.8, they (luckily) were available from ASTM material (not sure but I think it was under B564).
The dimensions they could be supplied in were per EN 1092-1 dimensions.

What I did is use our ASME VIII-1 app 2 calc sheet, or the modified VIII-2 calc. method, to determine the flange ratings, using EN 1092-1 dimensions. THe check was fairly simple, all that was needed were the ASTM B564 UNS N06625 material properties, gasket dimensions, etc. Furthermore I assumed a max external applied (piping) load on the flange, as most flanges feel some external force/moment due to thermal expansion.
The calc. quite easily showed they could be used under ASME application.

Reason why it had to be EN flanges was because of site standard (Dutch site, all connections as per EN 1092-1 flange spec).

If you can follow this route, all you need is to set up a calc. sheet. We use excel for this. Setting up the sheet costed us a few hours (near a hundred maybe), but it's a one time thing. Furthermore the sheet is an easy tool to check if any piping loads on a flange may introduce overstressing or leakage.

Hope this helps.

 

[XL83NL]

Correction; ASME VIII div 1 nor 2 isn't intended to be used for determining a possible leakage.
What we do in our sheets is determine a criterium for potential leakage, which is not a guarantee but more of a indication i suspect.
Just found this website; having checked the accuracy of the sheets but they may be of interest. (source for the link is this linkedin discussion)

 

[RPRad]

No offense taken, my first post was a bit misleading with DIN in the wording (the components in the system are from Germany so out of prior habit I refer to them as DIN but they correctly termed European (metric) flanges) and I wasnt clear with respect to why I was doing it this way.

Yes I have a spreadsheet set up to that effect so I guess I will I will end up doing that, I was hoping someone had gone through this before and either had a successful argument via the Code that I hadnt tried or had gone a little farther with the calculation leg work. Actually I will probably take another crack at getting them accepted under paragraph 304.7.2.(a) perhaps I can draw an equivalence between the EN Code and the B16.5 Code. I am sure their reason for not accepting them is principally based on the fact that they dont like the look of them more than its based on any specific technical issue...and it doesnt help that they are mixed into a piping system that is principally constructed with ASME materials, so the difference between the B16.5 flanges and En Flanges is glaring.

On the case of the European SRV I am just going to replace it with an ASME one...

Thanks

 

[tigny]

Hi,

There are at least two series of flanges norms in the European Standards (EN): PN designated (EN 1092 series) and CLASS designated (EN 1759 series).


As you may know EN 1759 norm is [highlight #C17D11]DIN[/highlight] EN 1759 in [highlight #C17D11]Germany[/highlight] or [highlight #729FCF]NF[/highlight] EN 1759 in [highlight #729FCF]France[/highlight], BS in the UK, etc.

The first part, EN 1759-1, is entitled (in english) Flanges and their joint — Circular flanges for pipes, valves, fittings and accessories,
Class designated — Part 1: Steel flanges, NPS ½ to 24.

Those are flanges originating from ANSI/ASME flanges, from ASME B16.5:1996 and other ASME standards (see below).
In the version I have (2004) there are still some discrepancies to the latest ASME codes (i.e. raised face is 1,6 mm instead of 2 mm).

It seems you can have "DIN" flanges with are relevant to ASME code (at least up to 1996 concerning B16.5) if you make use of DIN EN 1759.
With DIN EN 1092 there would be no such "direct" relevance.

Please get a copy and check it!

Remark: EN 1759 does not seem to give support to the essential requirements of European Directive 97/23/EC "Pressure Equipement" PED; EN 1092 does.

Normatives references cited in the EN 1759-1:2004 are (for the non EN or ISO):
ASME B16.5
ASME/ANSI B1.20.1
ASTM A105/A105M
ASTM A182/A182M
ASTM A203/A203M
ASTM A204/A204M
ASTM A216/A216M
ASTM A217/A217M
ASTM A240/A240M
ASTM A325
ASTM A350/A350M
ASTM A351/A351M
ASTM A352/A352M
ASTM A387/A387M
ASTM A515/A515M
ASTM A516/A516M
ASTM A537/A537M

 

[XL83NL]

Whats the real difference in EN 1759 and B16.5? They both have the class rating designation, like/similiar materials, ....
Is EN 1759 just the European way to accept B16.5 and copy paste that into a new document?
I've ever had a look into EN 1759. But given your reply you seem to imply this.

Then still, youre not using a listed component standard, which doesnt allow you to just use EN 1759 under B31.3, I think.

 

[RPRad]

I have had a closer look at the flanges in question and they are German and stamped EN 1092-1, and as noted above they are notably thinner than the 150# ASME flanges located adjacent to them. Fortunately the design pressure in this part of the system is 45 psig and the flanges have a 10 Bar (146 psig rating)so there should be enough breathing room there to hopefully get them through under an appendix 2 calc if necessary, if I dont get tripped up on the gasket seating stress. Per the discussion above I probably cant use the EN 1759 Code given these are stamped with the EN 1092 designation.

I did however look through the EN 1092 Code and it is pretty much laid out the same as B16.5 Code and has the temperature-pressure ratings as well, so I do think there is a legitimate argument to be made under B31.3 para 304.7.2. Fortunately the European flanges have only been used to make tie ins to the German equipment, so they are not widespread. However the next big issue will be registering the German pressure vessels as I will have to prove equivalency under ASME Section VIII....same game different animal