Large Diameter Flange design 3

[Mandeep1]

Hi colleagues,

I have some question on large diameter flange design. It is 72in (100 psi) flange operating at not very high temperature.

I started with a raised face flange.

Is there any benefit of using flat face v/s raised face v/s male-female type of flange face.

I can also try male-female type flange. But, in App. 2 calcs I probably have to take thickness from the bottom of the groove.

I saw AWWA flange standard, they are flat faced and not raised face. Is it for cost reason?

Are there are other concerns that I should consider in a large diameter flange.

Thanks,

best regards,
Mandeep Singh

 

[SnTMan]

Mandeep1, obviously a M/F flange will be thicker than a FF, but if you feel you need to confine the gasket it is necessary.

A 1/16" RF can be considered as part of the flange thickness in some cases, see Apx 2, Fig 2-4, gen. note (b).

In my opinion a RF allows for easier future maintenance machining than a FF. Don't know why the AWWA flanges are FF for sure, but FF flanges are common for full-face gaskets, which do not impose the flange moments that a narrow style gasket does.

Pay attention to the thickness of large, low pressure flanges. It will of course have to meet Apx 2 rotation requirements, but there is an old rule of thumb that says t >= sqrt(ID / 10).

Regards,

Mike

 

[Mandeep1]

Thanks Mike,

Thanks for the feedback. I checked the rule of thumb also.

The flange rotation controls here.

A colleague of mine brought it to my attention, that increasing the flange OD reduces the K factor and reduces the flange required thickness.

I read the Fig 2-4, gen. note (b), but could not under stand

I would prefer the gasket with outer ring as it would be easier to install and transport being almost 6 ft in diameter. The gasket is only 0.5 in wide.

Any other advice that should consider.

Thanks.

best regards,
Mandeep Singh

 

[JStephen]

AWWA flange standards are set up to bolt to cast-iron valves and fittings with full-face gaskets.

 

[SnTMan]

Mandeep1, gen note (b) just says that a 1/16" or less raised face may be included in the flange thickness, rather than added to.

If you are speaking of a spiral wound gasket I agree and would most likely use an inner ring as well.

Regards,

Mike

 

[vesselfab]

spiral wound gaskets at 72" diameter

i like camprofile in diameters over 30"

i think i would just go with a16.47 flanges either series whichever you plant generally uses.

 

[SnTMan]

B16.47 Scope is thru 60" only. Camprofile would be a good choice as well, as perhaps would a graphonic-style (corrugated metal, graphite faced).

Regards,

Mike

 

[Mandeep1]

Yes,

Thanks for bringing up good points.

The spiral wound gasket would have problems at large diameter.

I am considering Camprofile Flexitallic PN style gasket. They told me that it has metallic serrations so we do not really need an outer ring. I still like the gasket with outer ring (Camprofile style ZA) but is probably more expensive.

What would be a better choice?

best regards,
Mandeep Singh

 

[rmw]

If you are connecting piping to this flange, is it subject to B31.1? If so, there are some provisions regarding bolting of FF flanges to RF flanges with respect to class of bolting and acceptable types of gaskets. Spiral wound's aren't permitted if memory serves. (Maybe that is my company's design criterion.)

I'd recommend fabricating the 72" flange to the dimensional relationships of the B16.47. We have a vessel flange that size and do that and then treat it like a B16.47 flange for pipe connection purposes. The thickness, however is by the code calcs with the proper gasket factors, etc.

rmw

 

[saplanti]

If the connection is to be flange-to-flange and does not include standard or already manufactured valves, I would prefer special design for flanges for very large size piping like that. So you can make them economical by bringing the bolting PCD close to the OD of the pipe. You can go through AWWA and ASME B16.47 flanges, select the smallest PCD for the start and iterate it by going to smaller PCD as necessary. So, you need to look for your options.

If the gasket can be neopren, nitril rubber or silicon rubber (you need to check the temperature and chemical requirement) then you can use metal-to-metal contact flanges by alocation an o-ring groove on one side flange. In the hydraulic water power applications this is the most economical. This type of flange connection takes the prying forces into calculation and reduces the flange thickness as well.

In the flange design, as you know, the bolts have to take mostly the gasket forces if you do not use soft ring such as o-ring I mentioned. This will increase the required area of the bolts and increase the flange thickness.

Hope it helps.

Ibrahim Demir

 

[SnTMan]

Mandeep1, the outer ring on a camprofile gasket would normally only serve as a centering ring, if the flange were not a confined type joint. It would center the gasket against the bolting. Yes, it would cost more.

Regards,

Mike

 

[unclesyd]

Here is some data on the different types of large diameter flanges, along with their pressure and temperature ratings. I would definately check your flange design for gasket seating stresses IMHO seating a flexitallic could present a problem. We normally use a wire reinforced graphite gasket on the larger light weight flanges.

http://www.pacificflange.com/catalog.html

 

[Mandeep1]

Thanks to all of the comments,

B16.47 type flange gives a much thicker flange. I had to move the bolt circle diameter very close to the gasket to reduce the moment arm.

Hi Ibrahim,

Did you mean moving BCD close to OD? should it be other way round, closer to gasket reaction diameter G.

Hi Mike,

In your opinion a 72in 0.5 in wide kaam profile (flexpro) gasket would be without a outer ring. This is low pressure and temperature. Flexitallic engineer indicated that this is a stronger gasket as compared to spiral wound at larger diameter.

I was using the outer ring so that it would not get damaged during transportation and have easier installation.

If can go without an outer ring, I could BCD closer to gasket and reduce the flange thickness.

best regards,
Mandeep Singh

 

[saplanti]

Mandeep,

My comment for the PCD was a general approach. Of course, you are right with your comment. The gasket groove is going to be close to the inner diameter and PCD will follow. But, you have some restraints, for example the geaometry of the bolts and nuts, the other one is the code geometry requirements you may need to follow in case you need to use slope on the hub.

In my previous experience we completely eliminated the hub by making the flange thick enough and weld the pipe onto the flange by complete penetration butt weld. In this case you have planty space to fit the nuts and make the diameters smaller. O-ring groove say about 10-15 mm away from the inner edge might be sufficient to solve the sealing issue. This will reduce the pressure forces as well due to the reduced sealing diameter. There will be almost zero (ignore it in the calcs) gasket pressure load.

What else would you expect from a flange connection?

Regards,

Ibrahim Demir

 

[gr2vessels]

Mandeep1,
My two cents;-
At 72" diameter, the outer ring would hardly give you any additional structural strength to the Kamprofile Flexitalic gasket. I would instead opt for some guidance for the gasket, using a M/F facing. The additional flange thickness is minimal, since the gasket thickness at this dia should be only 4.3 mm (down to 3.2 mm fully compresse;- m=2 and Y=17.2).
Cheers,
gr2vessels

 

[SnTMan]

Mandeep1, a kammprofile is a pretty rugged gasket and would not likely need an outer ring for either serivce or handling. However, have some consideration for the field guys and provide some means to center the gasket when making up the joint. Either a M/F facing configuration or a centering ring on the gasket, which ever seems more practical for your application.

Regards,

Mike

 

[Mandeep1]

Thanks for the wisdom guys.




best regards,
Mandeep Singh

 

[Mandeep1]

I have one more question.

What would be the consideration for tongue-groove v/s male-female type flange.

Tongue-groove would be more confined and provide protection for gasket on ID and OD.

Tongue-groove can use a ring gasket, a smaller gasket than a M/F facing.

Why would you want to use a M/F type flange.

Do you have to worry about damaging of the tongue of the flange?


best regards,
Mandeep Singh

 

[Gorpomon]

SnTMan, can your further explain the rule of thumb:
t >= sqrt(ID / 10)
you listed in your first post, where did you find it? How does it apply to rotation? What reference books give it?

 

[Mandeep1]

Has any body seen welds with unequal legs. So, weld leg on one side is 0.5in. and on the other side is longer.

Try to increase the hub length of the flange. By increasing the weld length but only along the shell.



best regards,
Mandeep Singh