ANSI RAting of Flanges

[5188373]

There is one standard table which gives you maximum allowable pressure vs temperature rating of flanges. I just want to know that maximum allowable pressure in that is the design temperature or the working pressure. I mean to say the if a vessel operates at 1000 psig and its design pressure is 1500psig (for any reason) and its design temperature is 200F, what pressure rating we will use, 600# or 900#? If we consider max allowable pressure in above referred table, the ANSI rating shoule be 600#. On the otherhand, if we take this pressure as design pressure, it would be 900#.

 

[NozzleTwister]

5188373,

Refer to your applicable piping code; I'm most familiar with ASME B31.3.

You need to keep your flanges ratings within the design conditions as defined by your code. B31.3 allows you to exceed the rated pressure at the coincident temperature for short durations. The duration times and pressure limits are clearly defined in B31.3.

Another word of caution, there has been a number of changes to the rating pressures in ASME B16.5 and ASME B16.34, especially with alloys at higher temperatures. Make sure you are using the latest flange ratings for new work and the codes of record for existing systems.


NozzleTwister
Houston, Texas

 

[JLSeagull]

Use the design pressure and design temperature along with the correct material group to set the flange class. Perhaps the maximum pressure and temperature would not occur at the same time. If the maximum temperature is for one case and the maximum temperature is for a different case, consider the maximum pressure and temperature for case1 and the max pressure and temp for the other case -- then select the higher to set the flange class.

 

[dcasto]

Pressure-Temperature Ratings for Pipe Flanges and Flanged Fittings from ANSI B16.5-1996F Pressures are in pounds per square inch, gauge (psig)


CLASS 150 300 400 600 900 1500 2500
Temp F
–20 to 100 285 740 990 1480 2220 3705 6170
200 260 675 900 1350 2025 3375 5625
300 230 655 875 1315 1970 3280 5470
400 200 635 845 1270 1900 3170 5280
500 170 600 800 1200 1795 2995 4990
600 140 550 730 1095 1640 2735 4560
650 125 535 715 1075 1610 2685 4475
700 110 535 710 1065 1600 2665 4440
750 95 505 670 1010 1510 2520 4200
800 80 410 550 825 1235 2060 3430
850 65 270 355 535 805 1340 2230
900 50 170 230 345 515 860 1430
950 35 105 140 205 310 515 860
1000 20 50 70 105 155 260 430


Material Group 1.1 (Carbon Steel)
A105 (1), A216?WCB (1), A515?70 (1)
A516?70 (1) (2)
A350?LF2 (1), A537?C1.1 (3)

 

[JLSeagull]

There are many tables. One has the highest pressure and temperature rating for those meterials.

What are the materials that connect to the system?

What is the set pressure of the relief valve?

Material group 1.1 includes A 216 Grade WCB. Group 1.2 for A 216 Gr. WCC or A 352 Gr. LCC are rated a bit higer - up to 1500 psig at 100 degree F. Grade 2.3 for A 182 or A 240 Grades F316L and 304L are much lower. It is common to have flanged stainless steel instruments connected to the piping or vessel.

Material group 1.2 includes 1500 psig at 100 degree F.
This would apply to the A 203 Gr. B or Gr E plate for the vessel if you follow notes 1 and 2. However it would be unusual for the complete system protected by the pressure safety relief valve to comply with group 1.2. It might be possible to comply with group 1.1 rated 1480 psig at 100 degree F. I would expect some "non specification" Class 900 flanges for stainless, etc. The problem with these ratings is that too few people actually read them.

The process engineers often establish the relief valve settings to accommodate the operating upset conditions. This establishes the maximum pressure for the system. They also determine the maximum temperature and add some 50 degree F for the temperature.