ASME B16.5 PT Rating Tables Explained

Quick Answer: The ASME B16.5 PT rating tables list the maximum allowable working gauge pressure (psig) for flanged joints at specific temperatures. The tables are organized by material group number (e.g., Group 1.1 for A105, Group 2.1 for F304) and cover all seven pressure classes (150 through 2500). To use the tables, identify the flange material group, find the row matching the design temperature, and read the pressure for the desired class.

Structure of ASME B16.5 PT Tables

The PT rating tables in ASME B16.5 are arranged as follows:

Element	Description
Table number	Format: Table 2-[Material Group] (e.g., Table 2-1.1 for Group 1.1)
Rows	Temperature values in °F, from -20°F to the maximum for that material
Columns	Pressure classes: 150, 300, 400, 600, 900, 1500, 2500
Cell values	Maximum working gauge pressure in psig
Material groups	35+ groups covering carbon, alloy, stainless, and nickel alloy steels

Common Material Group Assignments

Material Group	ASTM Specifications	Typical Application
1.1	A105, A350 LF2, A216 WCB	Carbon steel flanges and valves
1.2	A350 LF6 Cl.1	Low-temperature carbon steel
1.5	A182 F12 Cl.1	1Cr-0.5Mo alloy steel
1.9	A182 F11 Cl.2	1.25Cr-0.5Mo alloy steel
1.10	A182 F22 Cl.3	2.25Cr-1Mo alloy steel
2.1	A182 F304, F304H	18Cr-8Ni austenitic stainless
2.2	A182 F321, F347	Stabilized austenitic stainless
2.3	A182 F316, F316H	16Cr-12Ni-2Mo austenitic stainless
3.1	A182 F51	Duplex stainless steel

How to Read the PT Tables: Step-by-Step

1. Identify the flange material from the piping specification or pipe class.
2. Find the material group from ASME B16.5 Table 1.A (e.g., A105 = Group 1.1).
3. Open the corresponding PT table (e.g., Table 2-1.1 for Group 1.1).
4. Locate the design temperature row. If the design temperature falls between two tabulated values, use the next higher temperature row (conservative) or interpolate linearly.
5. Read the maximum pressure for the desired pressure class from the corresponding column.
6. Verify the selected class provides a pressure rating equal to or greater than the system design pressure at the design temperature.

Interpolation Example

A system with design conditions of 350°F and 600 psig, using A105 flanges:

Step	Value
Material group	1.1 (A105)
Tabulated temperatures	300°F and 400°F
Class 300 at 300°F	655 psig
Class 300 at 400°F	635 psig
Interpolated at 350°F	645 psig
Design pressure	600 psig
Result	Class 300 is sufficient (645 > 600)

Pro Tip

For routine piping design, most engineers use the next higher tabulated temperature rather than interpolating. This provides a small additional safety margin and avoids calculation errors. Interpolation is most useful when the design pressure is close to the class boundary and upgrading to the next class would significantly increase project cost.

For the complete ASME B16.5 PT rating data across all material groups and pressure classes, refer to the flange rating guide. For flange type selection (weld neck, slip-on, blind), see the dedicated reference.

Read the full guide to flange ratings