Flange Face Selection Criteria

According to ASME B-31.3: (If you are using ASME)
1.-Determine Fluid Category (N/M/Lethal fluid/ Severe Cicle.........)

2.-ASME B31.3 Part 2 point 304.5

304.5 Pressure Design of Flanges and Blanks304.5.1 Flanges - General(a) Flanges not in accordance with para. 303, or304.5.1(b) or (d), shall be qualified as required bypara. 304.7.2.(b) A flange may be designed in accordance with theBPV Code, Section VIII, Division 1, Appendix 2, usingthe allowable stresses and temperature limits of the B31.3Code. Nomenclature shall be as defined in Appendix 2,except as follows:P = design gage pressureS, = bolt design stress at atmospheric temperatureSb = bolt design stress at design temperatureSf = product SEW [of the stress value S, the appropriatequality factor E from Table A-1A or A-lB,and weld joint strength reduction factor inaccordance with para. 302.3.5(e)] for flange orpipe material. See para. 302.3.2(e).(c) The rules in (b) above are not applicable to aflanged joint having a gasket that extends outside thebolts (usually to the outside diameter of the flange).(d) For flanges that make solid contact outside thebolts, Section VIII, Division 1, Appendix Y should beused.

3.- ASME VIII div1 Appendix 2
WP

Thanks your answer seems logical but as per ASME SEC V111 design of flange is not very easy and requires in depth knowledge. Thanks again.

What does the piping line specification require ? Oh.. wait.... you don't have one ?!

RF flanges are most common..

The Raised Face flange is preferred for several trades that have to work with them. They are much easier to install and replace. Only need to be spread slightly more than the thickness of the gasket vs. full working access to both flanges for the RTJ. A set of spreaders or banana wedges will suffice. It is also possible to "slip" or "drop" the new flange in with a raised face.

The raised face flange can be tightened up more than ordinarily necessary because the gasket is not limited by the faces of the flange touching as with the RTJ flange.

The raised face flange is also probably cheaper since the machining of the face is cheaper and simpler than the RTJ.

If at all possible use the raised face flanges. Much cheaper, easier and faster to work with than RTJ's. Also stocked by many more suppliers than RTJ's are.

Good Luck, Old Salt

Refrigerant piping, especially in the case of ammonia, typically uses RTJ flanges (also known as "tongue-and groove" or "retained gasket" flanges). I'm not sure if this is mandated by Code, but it is well established historical practice. Be cautious about using raised-face only, especially for dangerous or highly valuable fluids.