Explanation of Flanges

[davidrdguez]

Hello,

I am new here so I would like to greet everyone.

To start I bring a simple question, but I couldn't find information anywhere.

I have to design a water cooling system. In order to connect pipes, valves we use flanges.

This is going to be mounted in Germany. For example in one of the valves I have a DN80. According to some catalogues I see this 80 is not the inner diameter of the pipe attached to the flange. What does the 80 mean?

There are some existing flanges with outer diameter 285 mm, 8 holes and a bolt circle of 240 mm; I couldn't find a manufacturer with such type.

I was searching in Internet and in the forum, but I can't understand

Could you please explain me or give some link where this is explained?

Thanks in advance!

Cheers,

 

[hakkik]

1) Flange sizes related with the pipe size which they are connected to.
2) Pipe sizes are mostly defined as outer diameters but many roundings and exceptions. This is where the fun begins. The story is long but in short I suggest read from wikipedia article below. Although there is a relation as described at the article, i suggest do not try to calculate dimensions. Find the applicable std. and use tabulated values. For EN Flanges(old DIN) try EN-1092

http://en.wikipedia.org/wiki/Nominal_Pipe_Size

DN designation is created much later and compatible with the NPS system.
example DN80 pipe has same outer diameter with 3" pipe.

 

[pennpiper]

DN 80 is the metric designation for the size. The "D" is Diameter and "N" is Nominal.
DN 80 is relative equal to the American 3" NPS (Nominal Pipe Size). The two are not an exact match but are close.
Here is a link for a chart that gives you the Imperial and metric comparisons.

http://www.maselmon.com/Content.aspx?ContentID=24

Here is another chart that gives information about Flanges.

http://www.delvin.co.nz/flange.asp

 

[JohnGP]

Pennpiper,
I've been "metricated" for more than 30 years now, but my understanding is that DN80 pipe would exactly match NPS 3, and similarly for the other "pipe" sizes. I can't imagine pipe mills producing different ODs for DN and NPS pipe, but if that is the case, then I'm happy to be re-educated.

Cheers,
John

 

[micalbrch]

"DN" stands for nominal diameter as written by pennpiper. DN 80 stands for 80 mm inner diameter. It is not exactly 80 mm but depends upon the pressure stage. The pipe outer diameters are indentical for DN 80 pipes but the inner diameters depend upon the pressure stages and therefore upon the wall thicknesses. Example: A DN 150 pipe has a 168.3 mm outer diameter. Depending upon the pressure stage the inner diameter can be bigger or smaller than 150 mm.

A flange with a 285 mm outer diameter, 240 mm bolte circle and 8 holes is a DN 150 flange, PN 16 (nominal pressure 16 bar).

You can find a DIN flange catalogue here:

http://www.schoch-edelstahl.de/fileadmin/dokumente/produkte/SCHOCH_Flansche.pdf

 

[davidrdguez]

Hi everyone!

What a nice welcoming!

Thank you very much, I finally understood this issue, both pipes and flanges.

I'd like to add another question;

does every pipe have their own flange? or i can have a flange with the same pitch diameter but different nominal diameter, according to the links you gave me I understand there is only one flange for each nominal diameter.

This bring me to the next question:

If I a have a 200 mm diameter pipe, and I want to connect it with a 150 mm using flanges, how do i do?

Using a cone??

Using to flanges with same pitch diameter and different nominal diameter?

Thank you!

 

[Berndt]

David,

Flanges that fit one pipe size can have different pressure ratings. Thus even though two flanges can fit on the same pipe they will not have the same overall dimensions if they fall within different pressure classes. Flange dimensions for different pressure classes are specified in codes such as ASME B16.5 i.e. a CL150 3" flange will not bolt up to a CL300 3" flange even though both can be welded to a 3" pipe.

To connect two pipes with different diameters you would typically use what is referred to as a reducer. This is your cone option. Basic reducer dimensions will be specified in codes and are mostly off the shelf items.

 

[Struct71]

From the geometry that you have given (ODflange=285, pitch=240, 8 bolts) I can conclude that this is not a DN80/NPS3 ANSI B16.5 flange. Classes 150, 300, 400, 600, 900 1500 and 2500 have different dimensions.

 

[micalbrch]

Struct71: No, it is a DN 150 DIN/ISO flange, PN 16.

 

[Struct71]

Hmmm, a DN150 flange to fit a DN80 pipe. Intresting combination. Lots of welding to do.

 

[micalbrch]

No, no. There where two questions. One about the DN 80 pipe size and the second about the flange with the 240 mm bolt circle. At least that's how I understood it.

 

[davidrdguez]

Hi all,

Many nice answers!

Yes, the 168,3 outer diameter is a DN150

We have to go from this DN150 to a DN80 (the explanation is because we are using a control valve to reduce pressure, and another to reduce flow, so the IN/OUT of the valves are the DN80, the smaller, the cheaper)

I found this reducers, I understand we can weld the flanges to make the connection.

Also saw there are eccentric ones, which is the advantage?

Struct71, why do you say lots of welding? in the case we don't use flanges, isn't it?

I am learning a lot!

 

[pennpiper]

davidrdguez,

I recommend that you go to this website (

http://www.pipingdesigners.com/Training.htm)and

read every thing you find there. In "Section I, item "D" is a write-up on flanges. You may find that it answers most of your questions.

Other articles cover Pipe, Fittings, Gaskets & Bolts, as well as articles about Equipment and Layout issues. There are also articles on Shop Fabrication and Field Assignments.
Good reading!

 

[micalbrch]

davidrdguez: The difference between the eccentric and the conical reducers is the price. The eccentric ones are cheaper as far as I remember.

Struct71 understood your post in such a way that you want to connect a DN 150 flange directly to a DN 80 pipe.

 

[davidrdguez]

This page seems very good

I'm going deep into it!

 

[JohnGP]

micalbrch,

Concentric and eccentric reducers each have their application - you shouldn't choose which type to use based on price.

 

[racookpe1978]

I am surprised that your supervisor would leave you this much "learn by asking" for a system he (she?) actually wants designed.

Before you sign off your drawing and spec's - GET ANOTHER PERSON TO CHECK YOUR WORK!

You do not have the qual's yet to safely design a pipe system.

Yes, you are learning - and I applaud you for the courage to recognize you need to learn. But a person who does not know what an DN80 pipe is not qualified to prepare design and fabrication drawings yet for system carrying pressurized fluids.

Repeat: GET ANOTHER ENGINEER TO CHECK YOUR WORK.

 

[MJCronin]

david...

I think that your boss certainly has the right guy to design his piping system...!!

Good Luck !

-MJC

 

[davidrdguez]

Hi all,

My boss is an (excellent) physicist. I am the only engineer in my group and there are very few in the project.

This water cooling system is not my main occupation, the system is not very complex. The principal task for me was designing (with CAD software) the circuit from the pumps to the destination.

There are two older and experienced engineers who have the final saying.

I am learning a lot (from them and you!)

Thak you all!