Flange Rating
Flange Rating
(OP)
1. How do we decide the flange rating for pressure vessel? Based on the design pressure and MAWP?
2. If the flange rating is 150 psig and the hydrotest is UG-99(b) excluding the footnote 34, the hydrotest values came out higher than the flange rating of 150 psig. Will this detroy the flange?
Please answer my queries. Thanks.
Regards,
Darren
2. If the flange rating is 150 psig and the hydrotest is UG-99(b) excluding the footnote 34, the hydrotest values came out higher than the flange rating of 150 psig. Will this detroy the flange?
Please answer my queries. Thanks.
Regards,
Darren





RE: Flange Rating
RE: Flange Rating
2. Flanges can be hydro-ed up to 1.5 the ambient rating; see B16.5 para 2.6.
RE: Flange Rating
Regards,
Mike
RE: Flange Rating
just to expand a bit as it seems you're not very familiar with this, which worries me more than a little when you're messing about with pressure vessels, but flange rating is defined in ASME B 16.5 based on material type, flange class rating (150,300,600 etc) and Design temperature. There are then tables which give you MAWP for your flange. You can interpolate between the temperatures which go up in steps to get your particular temperature.
However hydrotest can be up to 150% of the pressure seen by the flange at test conditions (usually ambient pressure), hence usually higher than the MAWP at higher temperatures
I suspect you won't have a problem as your vessel MAWP and hence test pressure will be limited by the weakest component, which is not normally the flanges.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Flange Rating
Can someone explain so that i can understand .
RE: Flange Rating
RE: Flange Rating
You haven't indicated your vessel's design conditions and materials of construction.
Maybe your vessel's design temp. is high and the LSR for construction materials derive a high hydrostatic test pressure. In such case your vendor's explanation can make sense.
RE: Flange Rating
RE: flange hydro pressures; the max hydro pressure of a Class 300 SA-105 flange is 1080 psi, for 304 s/s it is 900 psi. see the part of B16.5 that XL83NL referenced.
RE: Flange Rating
As per B16.5:2013 that'll be (acc. my calcs) 1110 psi (1125 pis rounded) and 1080 psi (1100 psi rounded), respectively.
RE: Flange Rating
Do not agree with the philosophy to increase the equipment nozzle flange rating just to meet MAWP requirement. All the counter flanges on the piping shall also require higher rating compare to all other flanges and valves on the same piping.
All the piping flanges and valves also require higher rating if any future rerating/ debottlenecking by increasing pressure necessiate higher flange rating.
RE: Flange Rating
I will let a shell or head thickness limit the MAWP if there's a big jump between flange classes and hence big savings to be had in vessel cost by keeping the shell and head materials thinner. ASME VIII will let any component in the pressure envelope limit the MAWP- it doesn't tell you which one must limit.
If the selected plate thickness for the required MAWP is already sufficient to go up to the limit of the next higher flange class, then sure- why not go up a flange class on the nozzles? They don't cost much, usually. But it's rarely so in my experience.
RE: Flange Rating
Moltenmetal,
Going for next higher flange rating is not a small cost since up-gradation of only equipment flange and counter piping flanges will not help to achieve a higher rating for the complete system.
Complete piping flanges, valves and instrument shall also require upgradation for next higher rating which is going to cost a lot.
RE: Flange Rating
RE: Flange Rating
The difference between 150# and 300# in the cost of valves, instruments and (small) pipe flanges plus the nozzle flanges themselves is typically pretty small relative to the cost of the vessel in total. It might be worth the jump in nozzle flange class between 150# and 300# if the shell, heads etc. are all good for it already. But if you're jumping between 300# and 600# or between 600# and 900# (or 1500#- we rarely use 900#), or if you have to make a body flange thicker too, THAT would be a BIG jump in cost and availability and would be pretty much a pure waste of money in my opinion.
RE: Flange Rating
An interesting perspective. I've been brought up to agree with Duwe's philosophy but I could see that in some cases, particularly with relatively small vessels, your perspective would make sense. For the most part my company's spec's have been changed such that this won't be an issue; otherwise I might consider changing the "minor components shall not govern MAWP" requirement for small diameter vessels.
One concern I have with the "piping" approach is that it is not unusual to have high forces and moments at a vessel flange - often other flanges in piping can be designed in locations with less force and moment. One way some folks account for the forces and moments is to take an "equivalent pressure" approach and add that to the design pressure / MAWP to provide some margin against flange leaks. With the flanges max'ed out on pressure, there is no margin left for piping loads.
Another reason I like Eng-Tips: Philosophy can be much harder - and more interesting - to discuss than relatively simple code compliance. Just so long as everybody recognizes that with philosophy there will most likely not be one "right" answer!
RE: Flange Rating
Also you may wish to purchase this useful paper which an updated formula for the overconservative equivalent force/moment method.
RE: Flange Rating
1. Assuming that MAWP is limited by the flange rating which we do not want, we have following options;
a) Upgrade all the nozzle flanges to next higher rating. All the piping counter flanges, valves and instrument directly mounted on the equipment also require to have higher rating to connect with the nozzle flanges (rating of complete piping, flanges valves, instruments not upgraded). This will however not help in case of future de-bottlenecking as the complete system is not suitable for the higher rating.
b)Upgrade all the nozzle flanges along with the complete piping system (pipes, flanges, valves, instruments etc) to make it suitable for higher rating of the vessel. This may have a very big cost impact unless the piping circuit is a small circuit with low pressure rating and very few instruments, controls and valves. A big system even in low pressure rating (eg Nitrogen or Instrument air which is generally in 150# class and running all through the plant), if required to be upgraded to next higher rating just to meet vessel MAWP criteria, will have a big cost impact. Main process, high pressure systems with a lot of controls, instrumentation, valves will definetely have an extraordinary cost impact if we need to meet the criteria of "MAWP not to limit by flanges"
We also need to realize that most of the time piping class (pipe thickness)are based on flange rating pressure and not the process design pressure and change in flange rating will most likely require heavier pipe.
2. Above uprating and extra cost can not be justified for an unforseen future de-bottlenecking which may never happen also and if we are confident about future de-bottlenecking with increased pressure, why not select a higher design pressure from the day one?
3. Many times, I have personally seen that process design pressure is selected by based on the flange rating and not based on the actual operating pressure which may be much less compare to the design pressure. This is to allow any future de-bottlenecking upto the flange rating pressure without any change in the complete system (equipment, piping, valve, instruments etc). In such case, MAWP is mostly limited by flange and if I apply the criteria "MAWP not to be limited by flange", Its certainly overkill.
RE: Flange Rating
As to nozzle loads, the problems we encounter are usually with the nozzle necks rather than the flanges. And we find that the equivalent pressure method and all other methods we've examined for determining the effect of pipe stresses on flange leakage are excessively conservative below about 6" NPS.
RE: Flange Rating
The actual cost increase by using flanges of a high enough class to not be the limiting factor in the MAWP of a new vessel in the 'Real World' is so small that it disappears into the cost. The $$ may be less than the value of the scrap engendered in fabricating the vessel from stock sizes of pipe and plate. Don't believe me, call up the estimater at a vessel fab shop.
RE: Flange Rating
For Flange Pressure rating class 150 #,300#, 400# etc , the corresponding non-shock working pressure value permitted is 150 Psi, 300 Psi , 400 psi" etc which is known as "Primary pressure values" at "Primary temperature" . Primary temperature values are given for each Class of Flange, and material Groups.
Example: For Class 150# Flanges, of Material group 1.2 , Maximum working pressures are given bellow at different operating temperature.
-20 to 100 F --- 270 PSIG.
400F --- 180 PSIG
600F---- 150 PSIG( PRIMARY PRESSURE OF 150PSIG & PRIMARY TEMPERATURE @ 600F)
800F---- 75 PSIG
FOR Flange Class 300# and Higher class ratings ,the "Primary pressure Values" corresponds to higher" Primary temperatures" value of 850 F.
A pressure vessel design pressure and test pressure depends on process requirements and there is no manufacturing standard except design codes. Where as Flanges are manufactured to a standard ratings such as 150#,300# ,400 # etc for reasons of economy of Industrial production. One need to select the Flange rating which is very close and above the pressure vessel Design pressure&temperatures as per B 16.5 standards.
RE: Flange Rating