Flange Dimensions Class 300

Class 300 flanges per ASME B16.5 are used for moderate-to-high pressure piping services and are the second most common flange pressure class after Class 150. They are frequently specified for process piping in refineries, petrochemical plants, and gas processing facilities where design pressures exceed the Class 150 rating. At ambient temperature, a Class 300 carbon steel (ASTM A105) flange is rated for approximately 51 bar (740 psi).

Class 300 Flange Dimensions (ASME B16.5)

NPS	Flange OD (inch)	Flange OD (mm)	Thickness (inch)	Thickness (mm)	Bolt Circle Dia (inch)	Bolt Circle Dia (mm)	Bolt Hole Dia (inch)	No. of Bolts	Bolt Dia (inch)	Raised Face Dia (inch)	Raised Face Dia (mm)
1/2	3.75	95.3	0.56	14.3	2.62	66.5	0.62	4	1/2	1.19	30.2
3/4	4.62	117.5	0.62	15.7	3.25	82.6	0.75	4	5/8	1.50	38.1
1	4.88	124.0	0.69	17.5	3.50	88.9	0.75	4	5/8	1.94	49.3
1-1/4	5.25	133.4	0.75	19.1	3.88	98.6	0.75	4	5/8	2.31	58.7
1-1/2	6.12	155.4	0.81	20.6	4.50	114.3	0.88	4	3/4	2.56	65.0
2	6.50	165.1	0.88	22.4	5.00	127.0	0.75	8	5/8	3.31	84.1
2-1/2	7.50	190.5	1.00	25.4	5.88	149.4	0.88	8	3/4	3.94	100.1
3	8.25	209.6	1.12	28.4	6.62	168.1	0.88	8	3/4	4.62	117.3
3-1/2	9.00	228.6	1.19	30.2	7.25	184.2	0.88	8	3/4	5.25	133.4
4	10.75	273.1	1.25	31.8	9.00	228.6	0.88	8	3/4	5.31	134.9
5	11.00	279.4	1.38	35.1	9.25	235.0	0.88	8	3/4	6.44	163.6
6	12.50	317.5	1.44	36.6	10.62	269.7	0.88	12	3/4	7.56	192.0
8	15.00	381.0	1.62	41.1	13.00	330.2	1.00	12	7/8	9.19	233.4
10	17.50	444.5	1.88	47.8	15.25	387.4	1.12	16	1	11.31	287.3
12	20.50	520.7	1.88	47.8	17.75	450.9	1.25	16	1-1/8	13.00	330.2
14	23.00	584.2	2.12	53.8	20.25	514.4	1.25	20	1-1/8	14.00	355.6
16	25.50	647.7	2.25	57.2	22.50	571.5	1.38	20	1-1/4	16.00	406.4
18	28.00	711.2	2.38	60.5	24.75	628.7	1.38	24	1-1/4	18.00	457.2
20	30.50	774.7	2.50	63.5	27.00	685.8	1.38	24	1-1/4	20.00	508.0
24	36.00	914.4	2.69	68.3	33.00	838.2	1.62	24	1-1/2	23.75	603.2

All dimensions per ASME B16.5-2020. Thickness values are minimum for raised face (RF) flanges; the raised face height of 6.4 mm (1/4 in) for Class 300 is included in the thickness. Bolt hole diameter is 1/8 inch (3.2 mm) larger than the nominal bolt diameter.

Notes

• Applicable flange types: The OD, bolt circle, bolt holes, number of bolts, and bolt diameter values apply to all ASME B16.5 Class 300 flange types, including weld neck (WN), slip-on (SO), blind (BL), socket weld (SW), lap joint (LJ), and threaded (THD) flanges.
• Thickness variations: The outer envelope dimensions are the same across flange types, but the minimum flange thickness may vary slightly. The values in the table above represent the standard thickness for weld neck flanges; other types have slightly different thicknesses per ASME B16.5 Table 21.
• Raised face dimensions: Class 300 flanges have a raised face height of 6.4 mm (1/4 inch), which is four times the height of Class 150 raised faces. The raised face diameter shown is the contact area for the gasket.
• Bolt specifications: Bolts are stud bolts per ASME B16.5. Bolt holes straddle the natural centerlines of the flange. Class 300 flanges generally require more and larger bolts than Class 150 for the same NPS.
• Pressure rating: Class 300 carbon steel (ASTM A105) flanges are rated for approximately 51 bar (740 psi) at ambient temperature. The pressure-temperature rating decreases at elevated temperatures per the ASME B16.5 tables.
• Dimensional comparison with Class 150: Class 300 flanges have larger ODs, thicker bodies, and heavier bolting than Class 150 for any given NPS. For example, a 12-inch Class 300 flange has an OD of 20.50 inches versus 19.00 inches for Class 150, and requires 16 bolts versus 12.
• Reference standard: ASME B16.5-2020, Pipe Flanges and Flanged Fittings, NPS 1/2 Through NPS 24 Metric/Inch Standard.