Blind Flanges - Raised Face vs Flat Face

6

I can't recall ever seeing a flat faced flange for sale in real life. When I fabricate skillet blinds, I don't machine a raised face on them and they hold fine, so I would expect a flat faced blind flange to work as well, but I've never see one.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

I do not agree with David.

My rule is:
Flat Face against Flat Face
and
Raised Face against Raised Face
and
Ring Type Joint against Ring Type Joint

The questions include:
- (Material) When you mix any one of the above with another, what Gasket do you use?
- (Maintenance) How does the "miss match" get communicated to the maintenance people 5 or 10 years from now?
- (Safety) Is this a Hazop issue?
- (Design) Why would a properly educated, properly trained and properly experienced Piping Professional do this?

prognosis: Lead or Lag

Thanks zdas04 and pennpiper for your replies. I guess you can see why I reached out to this forum to help us here at work with our friendly discussion ! Personally, I had the same thought as pennpiper, but found myself on the far end of the spectrum. Basically those who think of themselves as savvy in the real application world of piping say that the "standard" way to do it is to use a RF flange with a different gasket, I guess a thicker version of the full face gasket. And I'm like "Why ?"

So pennpiper, could you point me to a manufacturer's website that I might get a good look at a Flat Face flange ?

I'm hoping for more discussion on this thread . Maybe we have established that there is no real standard ?

Thanks again and Good Day to all !

Sorry - I meant to sayI would like to see a manufacturer's website where I might get a good look at a Flat Face BLIND flange

This is the best I could find:

http://servicemetal.net/pdfs/125BlindFlanges.pdf

prognosis: Lead or Lag

I agree with pennpiper.

Whilst you might well get away with using RF flanges against a flat face flange, the risk is that the FF flange, espicially if it is a flange and not a machined end, will fail over time as the bending moment on the FF flange is much higher than it is designed for. In my experience FF flanges are found on cast iron and ductile iron materials and are done this way for a reason, which is that they don't like tension very much and can fail, especially when flexed repeatedly. If you mate a RF to a FF, you instantly create high loadings at the edge of the RF. Materials may have improved but in my youth I cracked a few flanges whilst tightening them up doing this exact thing....

FF flanges require FF gaskets - usually EPDM or some wort of uniform compressible material, not like RF gaskets.

Wow, this is GREAT ! Thank you all for taking time to respond !

Since the previous comment from Pennpiper, I actually contacted a major flange manufacturer and asked if they made the 150 LB Flat Faced Blind Flanges. They do, but when I asked for a cut sheet or a catalog, they don't have any. They said this was because “the ASME standard is raised face” and basically just use the special gasket.... "ASME/ANSI spec designed this series of flanges to be raised face as the industry standard for blinds, with flat face being an option (it’s still available, just less common)."

I still would like to confirm this is really the ASME approved and where that is documented, especially since I've heard the input from this forum. If anyone knows and can point me to such a publication, I would appreciate it.

Meanwhile, I'll try to pin down the issue with some of the engineers here.

Thanks again

Lots of people talk absolute rubbish about "ASME / ANSI says this or that" without any actual reference to fact. Always ask them for which code and section they refer to. The odd one or two that actually know their stuff will be able to reel it off straight away, everyone else will bluster. Look at the relevant sections in ASME B 16.5. normally suppliers make all the flanges in RF and then just machine off the RF bit to make a FF flange. All the other dimensions are the same. It's because FF is only normally used for cast or ductile Iron that you don't see it much in Oil and Gas, but much more in water and low pressure applications.

LittleInch, I know what you mean and you are exactly right - It's kind of a strange thing. Even some of the engineers distance themselves from some of these kinds of issues -I guess because it can get so convaluted.

I'd like to have access to the offical ASME documentation for myself.

I noticed that ASME.org has PDFs for sale individually. I'm not sure if that's really the best way to go - anyone tried any of those ? I think my boss would buy a set of books for the group to use.

We need piping component, valves, etc - but also we need material coding and definitions. We're in the pollution control industry - so a broad range but not ultra high temps and pressures.

Can anyone recommend a set of books or cds that we could purchase without breaking the budget ? We don't want the cheapest out there but the budget is not without limit - I'm thinking less than 5K for the whole set....

Thanks again !

You can buy direct from ASME, but also try IHS. Quite frankly if you're getting involved in things which need access to the latest codes and standards and you don't have them then you are running a big risk. The right documentation is as required as the right tools or equipment - without them you can't do your job properly. You probably only need 5 to 6 to start with. 5K (£ or $) will get you a long way.

Yes, I understand. Actually, the engineering group has access to what they need. It's just when we need answers it takes a long drawn out process to get to the gist of the issues. Like this issue we've been talking about. You can talk to 3 of them and get at least 2 different answers.

Part of the problem is they don't really understand what my group's challenges are, setting up Cats and Specs for PDMS. We want to be as accurate and concise as possible, but in their mind a general response is adequate and they don't have time for lenthy discussions. It's difficult for them to conceptualize what we are trying to accomplish.

The other part of the problem is that we are not pipers, nor mechanical engineers. We're software people. Some may think that several years of piping or engineering experience should be a prerequisite for PDMS administrators. I would not disagree, but good luck finding many people with those particular skill sets.

So, if we had ready access to the right documentation I think it would enable us to answer some of our own questions and eventually separate the facts from the B.S.

Thanks for the info - I actually already had a couple of items in my cart on the ASME website, but I need to do some digging to find out exactly what to buy.

I noticed eventual mention on this thread of gray cast iron and later ductile iron flanges, and also of water and wastewater applications typically of some lower pressure than cross-country oil and gas and some process steel lines. I believe traditional “B16.1” e.g. standards for cast iron flanges F&D 125 or less over many years have allowed either flat or raised face flanges, though F&D higher than that have been typically required to be raised face by that standard. A stipulation however was when flat face gray iron are mated to raised face, or when ring gaskets (that nest fully within the bolt circle, instead of “full face”) are employed with gray iron flanges, no higher maximum tensile strength than allowed for ASTM 307 Grade “B” steel bolts may be employed. Caveats concerning employing any higher strength bolts with gray iron flanges was carried over into other ANSI and eventual AWWA etc. standards or appendices copy, and also into some manufacturer’s literature(e.g. footnotes to page 8-4 table at http://www.american-usa.com/system/assets/146/orig...). While ring gaskets or raised faces convert bolt torque to greater compressive sealing stress on at least just a flat and not "special sealing" gasket, they also result in greater overturning moment (bending) on the flange itself than, compared to when the outer part of the flange from the bolt holes to the outer diameter is instead supported by a full-face gasket design (at least in the case of flat-faced matings).
While the standards many years later continue(d) to allow gray cast iron flanges, some major manufacturers switched many product lines to ductile iron flanges only many decades ago, as the newer material though very similar chemically had basically the same dimensions but roughly twice the strength and many times the toughness of the old gray iron (tolerating some imperfect assembly/ alignment, or application of bolting etc. with understandably fewer issues).
That being said, many old cast iron flanged pipelines at least with good assembly and support have remarkable records of durability. E.g. many kms of flanged joint cast iron pipelines were reportedly designed for the French “Sun King” Louis the Fourteenth, perhaps by the famous scientist Mariotte, to carry water to the grounds and fountains in Versailles. After original installation circa 1664, and some refurbishment last I think in about 2008, I understand roughly 80% of that piping is still in service now nearly three and a half centuries later (as near as I can tell, looking at a picture I have of a piece removed from that old pipeline, I think the flange faces of that piping were basically “flat”. Everyone have a good Easter weekend!)

FF flanges require FF gaskets - usually EPDM or some wort of uniform compressible material, not like RF gaskets.

I don't think this is always correct. If both flanges are of acceptable material (e.g. carbon steel), using a RF gasket between a FF & RF flange can be done. Although I'd agree it's not a "best practice" to mate a RF with a FF flange.

The trouble you run into, as mentioned above, is if you try to mate a RF carbon steel flange with a FF cast iron nozzle or similar. This can be the case with many of the older pump nozzles. You will be crack that cast iron FF nozzle at some point if you try to connect a RF carbon steel flange to it, due to the increased bending stresses toward the FF flange edges.

Hi LittleInch. I don't think "Look at the relevant sections in ASME B 16.5. normally suppliers make all the flanges in RF and then just machine off the RF bit to make a FF flange." is a correct fabrication process to get a FF flange. I am with a forging factory and we used to supply ASME FF W/N flanges to Saudi Arabian and Brazilian clients. You should never machine off the RF to get a FF surface because usually the flange thickness T of FF flange should be equal to T' of RF flange thickness plus t of RF thickness. I am not sure about cast/ductile iron flanges but that requires different forging mould.