Flange Pressure–Temperature Ratings (ASME B16.5)
The maximum working pressure of an ASME B16.5-2020 [1] flange, by material and temperature, for piping designers choosing a flange class. Pick the material group, or the ASTM grade, and the design temperature. The page gives the rating of every class from 150 to 2500, in bar and in psig, with the table notes that apply.
What the page covers
- Flange Rating Lookup: the working pressure for each class at the entered temperature, read from the rating tables of the chosen group.
- Rating Tables: the group’s bar/°C table (2-x.y) and psig/°F table (2-x.yC), with the rows the lookup used highlighted, then the grades in the group and their notes.
- Material Groups — Table 1.1-1: every forging, casting and plate grade of the steel and nickel alloy Groups 1 to 3, with a filter box.
Reading the results
B16.5 prints both tables, so the page shows each as printed and converts neither. A value marked “calculated” is interpolated linearly, never across classes or past a table's last row (para. 2.1). It is shown to 0.01 bar or 1 psig. A dash means the table gives no rating for that class. Superscripts on a grade are its note numbers. A note shown as a warning has a temperature limit or condition that applies at the entered temperature.
Limits and common mistakes
- B16.5 covers NPS 1/2 through NPS 24 only.
- The rating is for the flange. Bolting, the gasket and the piping code can all set a lower limit.
- Choose the grade, not just the group. A grade’s maximum temperature can be lower than its table’s last row, and the page blanks the ratings above it.
- Below −29 °C (−20 °F) the rating is capped at the first row (para. 2.4). Low-temperature toughness is a separate check.
Worked example
A hot oil line runs at 35 barg and 250 °C, with A105 forged steel flanges. Choose the flange class.
- Choose Material group 1.1 — C–Si, C–Mn–Si, C–Mn–Si–V, 3½Ni and ASTM grade (optional) A105 (Group 1.1).
- Enter Design temperature 250 with °C. The page shows 250 °C = 482 °F (calculated) and:
Table 2-1.1, 250 °C row:
Class 150 12.1 bar · Class 300 41.9 bar
Table 2-1.1C, between the 400 and 500 °F rows (calculated):
Class 150 175 psig · Class 300 610 psig - Read the note: Prolonged use above 425 °C (800 °F) is permitted but not recommended: the carbide phase may change to graphite. (note 1) It does not apply at 250 °C.
Class 150 (12.1 bar) is too low, and Class 300 (41.9 bar) covers 35 barg. Check: 41.9 bar × 14.504 = 608 psi, within 0.4 % of the 610 psig the °F table gives.
Flange Rating Lookup — ASME B16.5
Some of these materials lose toughness at low temperature, and the governing code may call for impact tests even above −7 °C (20 °F) (para. 5.1.2); joints with low-strength bolting are for Classes 150 and 300 only (para. 5.3.4).
Rating Tables
| Temp. (°C) | Class — working pressure, bar | ||||||
|---|---|---|---|---|---|---|---|
| 150 | 300 | 400 | 600 | 900 | 1500 | 2500 | |
| Temp. (°F) | Class — working pressure, psig | ||||||
|---|---|---|---|---|---|---|---|
| 150 | 300 | 400 | 600 | 900 | 1500 | 2500 | |
| Nominal designation | Forgings | Castings | Plates |
|---|
For Group 2 above 538 °C (1,000 °F), state the note requirements to the manufacturer (para. 5.1.3).
Material Groups — Table 1.1-1
| Group | Nominal designation | Forgings | Castings | Plates | Rating tables |
|---|
Plate grades are for blind flanges and reducing flanges without hubs only; an ASME Section II version of a grade may be used where its requirements match or exceed the ASTM ones [1]. Group 3 rows follow the rating-table headings, which list a few grades Table 1.1-1 omits; the first Group 3.6 row is printed three different ways (see its rating tables).