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Use of ASME B16.5 Standards for Flange Pressure Ratings

Engineers rely on ASME/ANSI standards and codes. The construction of the piping system helps to make sure that it meets the prescribed requirements of pressure integrity.

The standards and codes help to determine the characteristics of pressure integrity and simplify the design rules.

The difference between the codes and standards is helpful for the designers with detailed flange specifications and designs for the components. Here are the frequently encountered rules and standards:

1. Minimum wall flange thickness

2. Permissible materials for construction

3. Allowable work stresses

Structural behavior is due to the effects of thermal expansion, live loads, seismic loads, deadweight, internal pressure, and other imposed external or internal loads.

However, the piping codes provide no design rules for standard in-line components like standard valves and flange fitting components. The designing of these classes of elements happens through the reference to the industry standards.

1. Pressure-integrity standards: The standards help in providing uniform minimum-performance criteria. The designing and manufacturing of the components to the same standards will be helpful to function equivalently.

It helps to remember that pressure integrity is not entirely synonymous with leakage integrity.

During the operation and test, pressure integrity is one assurance when it comes to the leak-tight condition and does not account for the entire risk profile to the structural stability of the pressure boundary or added stresses.

2. Dimensional standards: The standards provide the configuration that helps in controlling the parameters for components. The primary purpose of these dimensional standards is to ensure that the manufacturing of similar parts by different suppliers will be physically interchangeable.

Conformity to the specified standards of ASME flange dimension during manufacturing a product doesn’t imply that the configuration of all such similar products will provide equal performance.

There are many different ASME standards for piping components that provide pressure-temperature ratings in their included “Reference Codes and Standards” sections.

As per the ASME B16.5, 2017, there are:

a. 16 nonferrous metal groups

b. 10 high-alloy steel material groups

c. 8 Low-alloy steel and carbon material group

If you want to check the complete lists and tables, you can check them on ASME B16.5, 2017. (Standard: “Pipe Flanges and Flanged Fittings: NPS ½ through NPS 24 Metric/Inch Standard”.)

The flanges with any material in the same group can easily carry the same pressure class of ASME flange and have the same pressure-temperature rating for almost any single material group.

The ASME B16.5 standard provides the 7 pressure classes for flanges. These are – 2500, 1500, 900, 600, 400 (less common today), 300 and 150. Class 75 also exists in ASME B16.47 Series B large diameter.

The rating for flanges in terms of pressure-temperature represents all the material groups organized within 44 tables. One table includes the ASME B16.5 2017 ed, for every material sub-group or group.

Table B2.1 is the adaption from ASME Standard B16.5 and is typical of the 34 flange rating tables that provide the pressure-temperature ratings for the flanges in the 2.1 material group.

The tables you will find below are organized as per the pressure classes that you can find at the top. At the left-hand border, you can also find the maximum working temperatures.

During the practice, using ASME B16.5 to determine the rating of the flange is relatively easy. Below is the recommended three-step process:

a. Determine the maximum temperature and operating pressure required for the flange.

b. You can select the material of the flange from the material groups of the 44 listed materials. Be aware of the qualifying notes that concern maximum operating temperatures for various materials that may influence the final material selection.

c. You must consult the right group table of material. You can start with the temperature listed in one increment higher than the desired maximum operating temperature.

Try to start with the Class 150 column and then proceed to the right until you find the proper pressure rating for the desired temperature, exceeding or equal to the required operating pressure.

The specified column that can satisfy the requirements can dictate the required pressure class and determine the actual pressure-temperature rating of the flange.

ASTM A182 is one of the chrome-based material specifications from material group 2.2.

If you consult Table B2.2 at a temperature of 650°F (343°C), a Class 600 flange has a rating of 890 psig (6136 kPa gage) at 650°F (343°C).

Table A1.1 Materials Used for ASME B16.5 Flange Construction (Partial Listing)

ASME B16.5 Flange Construction
Table B1.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 1.1 Materials

Table B1.1 Pressure-Temperature Ratings
Table B2.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.1 Materials

Table B2.1 Pressure-Temperature Ratings
Table B2.2 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.2 Materials

Table B2.2 Pressure-Temperature Ratings

If you still have any doubts about how to select flanges and what to look for, do let us know in the comment section or call us today!

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Tom Utriainen
Tom Utriainen
16 days ago

how do you select flanges when the design temperature of the system is less than -20 F?