Questions on "special" (tongue and groove and others) flanged connections

[MartinLe]

I need to consider "special" flanged connection for a pipeline: tongue and groove, male/female, ring type joint.

The medium is sewage gas at positive pressure <100mbar, ~40°C, the pipeline material is stainless steel, DN300, PN10

The reason for the range of flanges I consider is a specific german regulation, the TRBS2152 - flanged connections in gas systems create an ex-hazard zone unless they are one of the specified types or tested on a regular basis, and the connections in question will be hard to reach so the operator wants to avoid the checks.

Number one priority is of course reducing the number of flanges, but we will not arrive at zero.

These are my questions:

How to decide between the different flange types?
I tend towards nut and groove because these appear to be the most common and will definitly get feedback from the contractor (what do they have most experience with installing?)

So far I have not seen one of these as a loose flange. Are they available as loose flanges?

 

[XL83NL]

For such systems, Id use tongue and groove. We have had to deal with the same requirement about a year ago as well (German plant, German customer). I assume you have EN 1092-1 flanges. RTJ flanges for such pressures dont make sense. T&G are most easily made by machining the raised face portion into either a tongue or groove. Male/female could be considered as well, but I dont experience with those.

What do you mean by loose flanges? Lap joint types or something?

 

[MartinLe]

EN 1092-1 is correct.
I mean these types flanges:

 

[XL83NL]

I have no experience with such flanges in combination with T&G, but I'd use the one with the thickest facing, type 04.

 

[Caloooomi]

Is it the flange or the gasket that makes it leakproof? I tried looking up TRBS 2152 and all I could find was references to DIN EN 1591-1 and DIN EN 13555. A tongue and groove with a lap joint flange combined sounds a bit weird!

 

[MartinLe]

You can find it here (in german):

https://www.baua.de/DE/Angebote/Rec...e-Regeln/Regelwerk/TRBS/TRBS-2152-Teil-2.html

So far, I've seen no supplier who has the tongue and groove as a lap joint (Maybe impossible becaus of space constraints)

The TRBS speaks a diffferent language than other norms. In the TRBS, you have the terms "technisch dicht" and "auf Dauer technisch dicht" (leakproof, in the long run leakproof). Most detachable connections are considered leakproof - but not in the long run.

I think the logic behind the TRBS is that seals/gasets etc. could deform or fail otherwise. Why tongue and groove falnges aer deemd ok I don't know, maybe because the gaskets are locked in place.

 

[XL83NL]

Why tongue and groove falnges aer deemd ok I don't know, maybe because the gaskets are locked in place.

My recollection is the same; theyre blowout-resistant. Nevertheless, the sealing principe is similar to a raised face. The only thing different may be the sealing cross sectional surface.

I never really got to understood the TRBS. It gives a lot of freedom for interpretation:

(5) Auf Dauer technisch dichte Rohrleitungsverbindungen1 nach Absatz 2 Buchstabe a sind z. B.
1. unlösbare Verbindungen, z. B. geschweißt,
2. lösbare Verbindungen, die betriebsmäßig nur selten gelöst werden, z. B.

​

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a) Flansche mit Schweißlippendichtungen,

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b) Flansche mit Nut und Feder,

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c) Flansche mit Vor- und Rücksprung,

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d) Flansche mit V-Nuten und V-Nutdichtungen,

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e) Flansche mit glatter Dichtleiste und besonderen Dichtungen, wie z.B. Weichstoffdichtungen bis PN 25 bar, metallinnenrandgefasste Dichtungen oder metallummantelte Dichtungen, wenn bei Verwendung von Norm-Flanschen eine rechnerische Nachprüfung ausreichende Sicherheit gegen die Streckgrenze aufweist,

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f) metallisch dichtende Verbindungen in Leitungen größer als DN 32, ausgenommen Schneid- und Klemmringverbindungen.

z.B. means zum Beispiel (as Ive been told in my 5 yrs of German class). That means, to my understandig, that other options not listed, are not explicitly excluded, and therefore can be allowed.

Furthermore I agree with Caloomi, it's starnge to use T&G on a lap joint flange.

 

[LittleInch]

I don't think you'll find a lap joint in T&G or a slip on flange due to the amount of machining required.

The type of flange is important - O ring or flat ring to fit inside the groove?

All seems a bit overkill for low pressure gas, but if it gets the tick from the regulator then go for it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MartinLe]

Your (XL83NL) reading is correct. Other connections could be allowed. Pipe couplings and press fittings are not mentioned explicitly and there are differing interpretations floating about. At least I don't understand how e) is to be understood and how the calculation for safety against stretch limit should be done.

 

[XL83NL]

and there are differing interpretations floating about

That was our experience with this TRBS as well. Customer ultimately wanted T&G on a few flangesm, which we then supplied. Scope was small, so little impact.

At least I don't understand how e) is to be understood and how the calculation for safety against stretch limit should be done.

As I read it you have to do a calculation (of a standard, say EN 1092-1, flange) which proves the required leak tightness. Calculation shall be based on the elastic limit of a material (Rp0.2). Essentially an EN 1591-1 calculation.

 

[MartinLe]

Yes, the problem is that 1591-1 lets you calculate a connection for a tightness class (a term the TRBS does not know), while the TRBS mainly differentiates between "in the long run" or not (terms that don't appear in 1591). Or so I read, I don't have access to the 1591 right now.