4 replies to this topic

[kybele39]

Dear All,

Based on ASME 16.5, when flange rating is performed, do you use design tube metal temperature or fluid temperature?

I know we should use service/bulk/fluid temperatures. However for some reason between my co-workers there is a tendency to use design tube metal temperature for flange rating.

Could you please comment on the flange rating?

Thanks
Kybele

[fallah]

The design condition for flange rating is the maximum coincidental pressure and temperature condition that the flange is expected or allowed to sense.

Therefore, if the maximum coincidental temperature of your selected maximum pressure is design temperature your co-workers are right; otherwise you can use lower actual operating temperature.

Using design pressure and temperature for flange rating usually leads to a rating that would be a little bit conservative.

[kybele39]

Dear Fallah,

Thank you for the response. I do consider being conservative. However when you need 300lb flanges according to ASME B16.5, if you use 900lb. will cost a lot. Therefore I would like to understand; is it the outlet fluid temperature of a pressure vessel or tube metal temperature of the vessel should be used in flange rating?

For instance if your fluid temperature 800 deg.F and your tube metal temperature rated for 1200degF under 385psig design pressure based on the ASME 16.5 flange ratings is 300lb stainless steel flange is acceptable at the 410psig max. design pressure.

If you use 1200 deg.F temperature for flange rating then your flanges will be rated for 900lb at the 465psig max. design pressure.

If your operating pressure is 350psig why should you rate the flange for 465psig?

I hope I made my post clear enough to tell you guys my dilemma. Below I am giving the link you can easily calculate the flange rating.

http://www.gowelding.com/pv/flange.htm

Also the article below is referring to fluid temperature.

http://www.flowcontr...p?ArticleID=180

Thanks to all

K.

Edited by kybele39, 27 July 2010 - 03:05 PM.

[fallah]

Dear Fallah,

Thank you for the response. I do consider being conservative. However when you need 300lb flanges according to ASME B16.5, if you use 900lb. will cost a lot. Therefore I would like to understand; is it the outlet fluid temperature of a pressure vessel or tube metal temperature of the vessel should be used in flange rating?

For instance if your fluid temperature 800 deg.F and your tube metal temperature rated for 1200degF under 385psig design pressure based on the ASME 16.5 flange ratings is 300lb stainless steel flange is acceptable at the 410psig max. design pressure.

If you use 1200 deg.F temperature for flange rating then your flanges will be rated for 900lb at the 465psig max. design pressure.

If your operating pressure is 350psig why should you rate the flange for 465psig?

I hope I made my post clear enough to tell you guys my dilemma. Below I am giving the link you can easily calculate the flange rating.

http://www.gowelding.com/pv/flange.htm

Also the article below is referring to fluid temperature.

http://www.flowcontr...p?ArticleID=180

Thanks to all

K.

Dear Kybele,

Seems you pay special attention to the temperature for flange rating,while as i mentioned in my previous post,flange rating is performed based on the maximum coincidental pressure and temperature condition that the flange is expected or allowed to sense.Of course,fluid temperature to be given as the temperature the flange material would sense.In fact,it is assumed flange material don't sense any temperature higher than maximum fluid temperature.There are exceptions such as considering sunshine temperature (usually 85 C) for the cases in which piping system would be outdoor and fluid temperature is lower than 85 C when effect of sunshine heating not to be considered.

As you can see in ASME B16.5 flanges,in any rating,can withstand different pressures at different temperatures and if ,let say,temperature increases the pressure that mentioned flange can withstand would be decreased.The important thing should be considered is the flange which its rating specified would cover all the maximum coincidental pressure and temperature condition that may occur for it and in most cases using design pressure and temperature (provided that no considerable difference between operating and design values in both) leading to a proper rating.

For the cases with considerable difference between operating and design value of pressure/temperature,to avoid the rating higher than required one can (IMO) consider two coincidental condition:
-Design pressure with coincidental operating temperature
-Design temperature with coincidental operating pressure

And after determination of the rating for each of two condition the higher value to be given as flange rating.

Edited by fallah, 28 July 2010 - 01:50 AM.

[kybele39]

Dear Fallah,

Thank you very much for your response. Appreciate it.

K