flange facings- tongue and groove versus raised face

[kennymcmack]

What are the advantages/disadvantages between tongue and groove, raised face, flat face, and male and female face flanges? Also, why are there some gaskets made from soft material but some are made from solid metal, like aluminum? Thanks

 

[gerhardl]

A complete answer would be long and complicated, but all have to do with service type, sizes, pressure classes, temperature and liquid.

Secondly: availabillity, normal practice/use and demands and price.

For most 'normal' sizes, pressure classes and services raised face and soft or reinforced flange sealings will be sufficient.

An O-ring groove with adapted O-ring special selected material against flat face or male counterflange will hva better sealing properties, but will be higher in price, and require more controlled handling and thightening when mounting.

 

[btrueblood]

Another reason for tongue-and-groove flanges is to provide more accurate centering of the flanges (e.g. upstream of a fluid metering orifice).

 

[rconner]

Interesting questions. Basic concepts and applications of bolted flanged joints are of course now hundreds of years old, and I believe you could find much on the theories and practice of much bolted flanged joint design with an internet search. e.g. I plugged the key words “bolted flange joint” into “Google” and got 1.3+ million “hits”.
I believe also by plugging the keywords "raised face flange" into the "Advanced Search" feature of these forums, you will also find there have been multiple past discussions of raised vs flat face (while not necessary for all applications, raised face concentrates gasket-sealing pressures where they are arguably most needed). Some of these sites might not be a bad read if you have the time. Nevertheless, as is indicated by this inquiry, there is still a surprising lack of basic information and I think a lot of misunderstanding concerning applications of the various components. I am aware that bolted flanged connections have been made with virtually all kinds of widely varying material flanges, bolts, gaskets of all manner of materials and hardnesses (from quite hard to quite soft), and even some assemblies even forpressure service without any gaskets at all! I think I have heard some early gaskets were perhaps mostly of lead or skins/leather etc.
Other than that, I will only share some experience I once saw with some large diameter (48”), not extremely high pressure nor uncommon, flanged piping on a water storage/conveyance project several years ago. On that project the contractor encountered many leaks in filling the lines with water that he was unable to remedy with normal bolt tightening. In researching these problems (of course after the fact), I was told that the Contractor had employed rather thin, flat gaskets of a quite hard specialty material (that they said had been developed by NASA, and for which they had reportedly paid in excess of a thousand USD for each gasket). To make a long story short, while a lot of factors might contribute to flanged joint leakage problems, not the least of which is workmanship with such labor-intensive and labor-reliant designs, I understand the Contractor on that particular job corrected every leak by replacing those extremely expensive gaskets with the resilient molded rubber gaskets shown in “ADIP Table 8-2 at the site

http://www.acipco.com/adip/pipe/flanged/dda.cfm

(these gaskets, that I understand were just a small fraction of the cost of the initially installed gaskets on that job, sort of combine the features of conventional full-face flat gaskets with an additional “torus,” or o-ring sealing concept).
Now if the application would have instead involved hundreds of degrees F. temperature and/or thousands of psi pressure, maybe some sort of suitably resistant harder gasket (and perhaps also more formidable bolting?) would have been a better choice. I believe additionally, resilient gaskets or flanges with special sealing features like bulbs or o-rings etc. have been shown in some common applications to be generally/understandably some more tolerant of structural loadings, deformations/misalignment of flanges, and more imperfect cleaning and/or bolting etc. than simple flat gaskets. As I’ve heard kind of catchily described by another in response to these lists, its sort of a “horses for courses” matter.

 

[gerhardl]

rconner-

interesting!

This is of course the 'other side' of the flange discussion, how to select proper sealings and have sufficent force and resulting sealing geometry to compress to seal properly.

Many engineers do not have in mind the simple fact that an O-ring for an O-ring grove of a flange must be selcted properly both on hardness, material and geometry and be thightened to correct compression. If mismatched to the grove physically : too large -> might float and be damaged, Too small - > might be displaced in groove and/or not compressed properly. All leading to leakage.

(Supporting rings in other materials might help if exact matching O-rings are not available.)