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ANSI FLANGE PRESSURE RATING EXPLAINED

Now consider what this means in terms of pressure rating:

At a temperature of 600 degrees F°, the class 150 flange can sustain only 140 psi (as per the rating chart below)
The class 300 flange (which is larger and stronger but has the same hole size) can sustain 570 psi at 600 degrees F°.
Finally, a class 2500 flange of the same size can withstand 34 times the pressure of a class 150 flange, with a rating of 4730 psi at 600 F°!

Scroll down to see the rating table that pertains to your flange (this depends on the material of the flange, as flanges with different material grades have different pressure ratings)
Determine your piping system’s maximum working temperature (i.e. select one line in the table)
Choose a rating based on the expected maximum pressure at that temperature level (i.e. select one column in that line)
You’ve now received the required rating!
Below are the ASME B16.34 pressure rating charts for the most common flange materials to assist you (carbon, alloy, stainless).

Pressure rating is the highest amount of pressure that a flange can handle as the temperature rises. The ANSI/ASME B16.5 standard lists seven pressure ratings for flanges: 150, 300, 400, 600, 900, 1500, and 2500.
The terms “pressure rating,” “class,” “#,” “Lb,” and “Lbs” all mean the same thing when it comes to how a flange handles pressure and temperature (and other equipment like valves, fittings, etc).

Let’s use an example to make this clear:

If two flanges have the same bore size, say 6 inches, and the same material, say A105, but different pressure ratings, say class 150 and class 300, the class 150 flange will be smaller, lighter, and less sturdy than the class 300 flange (class 300). This is what the picture shows:

How the Flange Rating System Works

People who are new to the pipe industry frequently have difficulty understanding how flange rating works. Let us first define a flange and the role it plays in the plumbing sector before proceeding with the discussion.

What exactly is a flange and how does it work?

A flange is a piece of equipment that connects pipes, pumps, valves, and other piping components to form a pipeline system. The flange is an important part of the piping system because it allows for easier cleaning, inspection, and modification. Weld Neck Flange, Slip-on Flange, Socket Weld Flanges, Lap Joint Flange, Threaded flange, Blind flange, Orifice flanges, Reducing flanges, and many other types of flanges are available.

What is the flange rating and how does it work?

It’s crucial to make sure that the flanges used in the oil, gas, and petrochemical industries can resist the pressures and temperatures they’re exposed to. Not only is the size of the flanges significant, but so is the rating. As a result, selecting a flange with the appropriate rating ensures that it can endure the pressures of functioning at different temperatures.

The maximum pressure that a flange can withstand at high or increasing temperatures is defined by the class of the flange. Flanges having a higher flange rating or flange class are naturally considered stronger since they can withstand more pressure at higher temperatures.

The ASME B16.5 standard, which applies to flanged fittings and pipe flanges, is the industry standard for flanges. This contains flanges with diameters ranging from 12″ NPS to 24″ NPS.

As a result, as the temperature rises, the maximum allowable pressure falls. With the following example, the notion of flange rating can be readily described.

A Class 300 flange can resist higher pressure than a Class 150 flange because it is made of more metal and can tolerate more pressure. However, a flange’s pressure capability is affected by a number of factors.

Because it is comprised of more metal and can withstand more pressure, a Class 300 flange can withstand higher pressure than a Class 150 flange. The pressure capability of a flange, on the other hand, is influenced by a variety of elements.

CARBON STEEL FLANGE RATING CHART

Carbon steel flange pressure-temperature rating ASME

ANSI FLANGE ASTM A105, A350 Gr. LF2/LF6 Class 1

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI – is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature (in F°)150#300#400#600#900#1500#2500#
< 1002857409851480222037056170
2002606809051360203533955655
3002306558701310196532705450
4002006358451265190031705280
5001706058051205181030155025
6001405707551135170528404730
6501255507301100165027454575
7001105307101060159026554425
750955056751015152025354230
80080410550825123520553430
8506532042564095515952655
9005023030546069011501915
950351351852754106851145
10002085115170255430715
Hydrostatic Test Pressure (in Psig)450112515002225335055759275

Notes

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in bars – is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature in C°150#300#400#600#900#1500#2500#
   -29 / 3819.651.168.1102.1153.2255.3425.5
5019.250.166.8100.2150.4250.6417.7
10017.746.662.193.2139.8233388.3
15015.845.160.190.2135.2225.4375.6
20013.843.858.487.6131.4219365
25012.141.955.983.9125.8209.7349.5
30010.239.853.179.6119.5199.1331.8
3259.338.751.677.4116.1193.6322.6
3508.437.650.175.1112.7187.8313
3757.436.448.572.7109.1181.8303.1
4006.534.746.369.4104.2173.6289.3
4255.528.838.457.586.3143.8239.7
4504.62330.74669115191.7
4753.717.423.234.952.387.2145.3
5002.811.815.723.535.358.897.9

Notes:

ASTM A105: Long-term exposure to temperatures above 425°C transforms steel’s carbide phase to graphite (this material is not recommended for consistent temperatures above this number).

The ASTM A350 LF6 standard states that it should not be utilized at temperatures above 260 degrees Celsius.

ANSI FLANGE ASTM A350 Gr. LF3, A350 LF6, Class 2

The flange rating chart depicts the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at various temperatures (in degrees Celsius or Fahrenheit) – in PSI.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature in °F150#300#400#600#900#1500#2500#
-20 to 10029075010001500225037506250
20026075010001500225037506250
3002307309701455218536406070
4002007059401410211535305880
5001706658851330199533255540
6001406058051210181530255040
6501255907851175176529404905
7001105707551135170528404730
750955056701010151025204200
80080410550825123520603430
8506527035553580513402230
900501702303455158601430
95035105140205310515860
1000205070105155260430

ANSI FLANGE ASTM A350 Gr. LF1 

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) — in PSI — is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature °F150#300#400#600#900#1500#2500#
-20 to 1002356208251235185030851545
2002155607501125168528104680
3002105507301095164027354560
4002005307051060158526454405
500170500665995149524904150
600140455610915137022853805
650125450600895134522453740
700110450600895134522453740
75095445590885132522103685
80080370495740111018503085
8506527035553580513402230
900501702303455158601430
95035105140205310515860
1000205070105155260430

ALLOY STEEL FLANGE RATING CHART

Alloy steel flange pressure-temperature rating ASME

ANSI FLANGE ASTM A182 Gr. F1 (Chrome Moly)

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (in Celsius or Fahrenheit) – in PSI – is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature °F150#300#400#600#900#1500#2500#
-20 to 1002656959251390208534705785
2002606809051360203533955660
3002306558701305195532605435
4002006408551280192032005330
5001706208301245186531055180
6001406058051210181530255040
6501255907851175176529404905
7001105707551135170528404730
750955307101065159526604430
800805106751015152525404230
85065485650975146024354060
90050450600900135022453745
9503528037556084514052345
1000201652203304958251370

STAINLESS STEEL FLANGE RATING CHART

ANSI FLANGE ASTM A182 Gr. F304, 304L

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI – is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature °F150#300#400#600#900#1500#2500#
-20 to 1002757209601440216036006000
2002306008001200180030005000
3002055407201080162027004500
400190495660995149024854140
500170465620930139523303880
600140435580875131021853640
650125430575860129021503580
700110425565850127521253540
75095415555830124520753460
80080405540805121020153360
85065395530790119019803300
90050390520780116519453240
95035380510765114519103180
10002032043064096516052675
10502031041061592515452570
11002025534551577012852145
1150202002654005959951655
1200201552053104657701285
125020115150225340565945
13002085115170255430715
1350206080125185310515
140020506595145240400
145015354570105170285
15001025355580135230

The maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI – is shown in the flange rating table.

ANSI/ASME B16.34ANSI PRESSURE RATING
Temperature °F150#300#400#600#900#1500#2500#
-20 to 1002757209601440216036006000
2002356208251240186030955160
3002155607451120168027954660
4001955156851025154025704280
500170480635955143523903980
600140450600900135522553760
650125445590890133022203700
700110430580870130521703620
75095425570855128021353560
80080420565845126521103520
85065420555835125520903480
90050415555830124520753460
95035385515775116019303220
100020350465700105017502915
105020345460685103017202865
11002030540561091515252545
11502023531547571011851970
1200201852453705559251545
1250201451952954407351230
130020115155235350585970
13502095130190290480800
14002075100150225380630
1450206080115175290485
150020405585125205345

Read More :

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