How Does the Flange Rating Work?

ANSI FLANGE PRESSURE RATING EXPLAINED

Now think about what this means for the rating of pressure:

At 600 degrees F, the class 150 flange can only handle 140 pounds per square inch (psi) (as per the rating chart below)

The class 300 flange, which is bigger and stronger but has the same size hole, can handle 570 psi at 600 degrees F°.

Lastly, a class 2500 flange of the same size can withstand 4730 psi at 600 F°, which is 34 times more pressure than a class 150 flange of the same size.

Scroll down to see the table for your flange’s rating (this depends on the material of the flange, as flanges with different material grades have different pressure ratings)

Find out the highest temperature that your piping system can handle (i.e. select one line in the table)

Choose a rating based on the highest pressure you expect to see at that temperature (i.e. select one column in that line)

You now have the rating you needed!

Here are charts from ASME B16.34 that show how much pressure can be put on the most common flange materials (carbon, alloy, stainless).

Pressure rating is the most pressure a flange can handle as the temperature rises. The ANSI/ASME B16.5 standard says that flanges can handle pressures of 150, 300, 400, 600, 900, 1500, and 2500.

When it comes to how a flange manages pressure and temperature, the phrases “pressure rating,” “class,” “#,” “Lb,” and “Lbs” all signify the same thing (and other equipment like valves, fittings, etc).

Let’s look at an example to explain:

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 strong than the class 300 flange (class 300). What the picture shows is this:

The Flange Rating System and How It Works

Flange rating is often hard to understand for people who are new to the pipe industry. Before we go any further, let’s talk about what a flange is and what it does in the plumbing world.

What is a flange, and how does it do what it does?

A flange is a piece of equipment that connects pipes, pumps, valves, and other piping parts to make a pipeline system. The flange is a key part of the piping system because it makes cleaning, checking, and making changes easier. There are many different kinds of flanges, such as Weld Neck Flange, Slip-on Flange, Socket Weld Flanges, Lap Joint Flange, Threaded Flange, Blind Flange, Orifice Flanges, Reducing Flanges, and Blind Flanges.

How does the flange rating work, and what is it?

In the oil, gas, and petrochemical industries, it’s important to make sure that the flanges can handle the pressures and temperatures they’re put through. The size of the flanges is important, but the rating is also important. So, choosing a flange with the right rating makes sure it can handle the stresses of working at different temperatures.

The class of the flange tells how much pressure a flange can handle when the temperature is high or rising. Flanges with a higher flange rating or flange class are thought to be stronger because they can handle more pressure at higher temperatures.

The industry standard for flanges is the ASME B16.5 standard, which is used for both flanged fittings and pipe flanges. This has flanges with diameters between 12′′ NPS and 24′′ NPS.

So, when the temperature goes up, the maximum pressure goes down. Flange rating is easy to explain with the help of the following example.

A Class 300 flange can handle more pressure than a Class 150 flange because it is made of more metal and can handle more pressure. But there are many things that can change how much pressure a flange can handle.

A Class 300 flange can handle more pressure than a Class 150 flange because it is made of more metal and can handle more pressure. On the other hand, different things affect how much pressure a flange can handle.

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 says that when steel is heated above 425°C for a long time, its carbide phase changes into graphite (this material is not recommended for consistent temperatures above this number).

According to the ASTM A350 LF6 standard, it shouldn’t be used at temperatures higher than 260 degrees Celsius.

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

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

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

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

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 :

Understanding how stainless steel pipes can be used in different fields: Because welded pipes are so versatile, they can be used in almost any kind of business. Because of this, though, they do better at resisting corrosion and less well at resisting pressure than they do at resisting rust. Welded pipes are a lot easier to work with than most other types of pipes.

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