Hello.

What does it mean when a specification says that "The MAWP of the vesse lshould not be limited by flange rating".

Thanks a lot.

I really appreciate it.

The author of the specification wants you to calculate the MAWP of the pressure vessel (see definition of MAWP in ASME VIII, Div 1, Appendix 3). He further requires that the MAWP of the vessel cannot be limited by a flange; this means that the vessel MAWP must be limited by some other condition, such as thickness of a shell or head, or by nozzle reinforcing area, or any of the other criteria that may possibly limit the MAWP. The MAWP of a flange on the vessel cannot be the smallest MAWP of the MAWPs calculated for each of the vessel components.

However, the requirement as written does not indicate if this applies only to "standard" ASME B16.5/B16.47 flanges or if it applies also to flanges designed to Appendix 2. It is common to require that the vessel MAWP should not be limited by the pressure-temperature rating of B16.5/B16.47 flanges. But not so common to require that an Appendix 2 flange should not limit.

Further, the requirement as written would apply to flanges on nozzles as well as to body flanges (body flanges may connect shell courses, etc). Again, it is not so common to require that body flanges may not limit the vessel MAWP.

thanks Tom.

You have given a great reply.

Thanks for taking out so much time for this query. I really appreciate it.

I have come across this requirement of "MAWP should not be limited by flange" but personally I am not very comfortable with this requirement and many of our projects we could convince client to change this.

Many times design pressure is selected based on P/T rating of the flange and in such cases MAWP will be limited by flanges else you need to select next higher rating. Connected piping flange shall have flanges based on P/T rating and may not match with the equipment flange if higher rating is selected.

you need to check/ discuss with client whether it is really required and wish to implement this requirement. If yes, you need to be careful since you may need to select higher pressure rating flanges.

Regards

Dangerous clause if you have this please take care- But as sanjeev said ask client to re consider it manyier times your vessel thk 10 mm pipe sch 40 and Flange will be 300 # or higher ratings which looks very odd and undesirable .

_________________
Niraj