Class 150 Flange Dimensions (ASME B16.5)

Quick Answer

Class 150 is the most commonly used flange pressure rating in the oil and gas industry. It covers low-to-moderate pressure services and is the default rating for utility piping, cooling water, and low-pressure process lines. The dimensions below are per ASME B16.5 for welding neck (WN) flanges with raised face (RF).

Class 150 flanges are rated for a maximum working pressure of approximately 19.6 bar (285 psi) at ambient temperature for carbon steel (ASTM A105). The pressure rating decreases at elevated temperatures per the ASME B16.5 pressure-temperature tables.

Class 150 Welding Neck Flange Dimensions (ASME B16.5)

NPS	DN	Flange OD (mm)	Thickness (mm)	Raised Face Dia. (mm)	Bolt Circle (mm)	No. of Bolts	Bolt Dia. (in)	Bolt Hole Dia. (mm)
1/2	15	89.0	11.2	34.9	60.5	4	1/2	15.7
3/4	20	98.5	12.7	42.9	69.9	4	1/2	15.7
1	25	108.0	14.2	50.8	79.2	4	1/2	15.7
1-1/4	32	117.5	15.7	63.5	88.9	4	1/2	15.7
1-1/2	40	127.0	17.5	73.2	98.6	4	1/2	15.7
2	50	152.4	19.1	92.1	120.7	4	5/8	19.1
2-1/2	65	177.8	22.4	104.6	139.7	4	5/8	19.1
3	80	190.5	23.9	127.0	152.4	4	5/8	19.1
4	100	228.6	23.9	157.2	190.5	8	5/8	19.1
5	125	254.0	23.9	185.7	215.9	8	3/4	22.4
6	150	279.4	25.4	215.9	241.3	8	3/4	22.4
8	200	342.9	28.4	269.7	298.5	8	3/4	22.4
10	250	406.4	30.2	323.9	362.0	12	7/8	25.4
12	300	482.6	31.8	381.0	431.8	12	7/8	25.4
14	350	533.4	35.1	412.8	476.3	12	1	28.4
16	400	596.9	36.6	469.9	539.8	16	1	28.4
18	450	635.0	39.6	533.4	577.9	16	1-1/8	31.8
20	500	698.5	42.9	584.2	635.0	20	1-1/8	31.8
24	600	812.8	47.8	692.2	749.3	20	1-1/4	35.1

Dimensions per ASME B16.5-2020 for welding neck flanges. Raised face height is 1.6 mm (1/16 in), included in the thickness value.

Key Dimensions Explained

Flange OD: Overall outside diameter of the flange. Determines the space envelope for piping layout and support design.

Raised Face Diameter: The diameter of the raised face (RF) that contacts the gasket. The gasket ID and OD must match this dimension.

Bolt Circle Diameter (BCD): The diameter of the imaginary circle passing through the center of all bolt holes. Critical for bolt pattern alignment.

Number of Bolts: Always a multiple of 4 for ASME B16.5 flanges. The bolt holes are equally spaced and straddle the centerlines (not on the centerlines).

Bolt Diameter: Refers to the stud bolt nominal diameter. Bolt holes are drilled 3.2 mm (1/8 in) larger than the bolt diameter.

Pro Tip

When ordering Class 150 flanges, always confirm the face type (RF, FF, or RTJ) as it affects the flange thickness and gasket selection. Raised face is the default for Class 150 in most oil and gas specifications. Flat face (FF) is used when mating with cast iron flanges or equipment nozzles per ASME B16.1.

For detailed welding neck flange dimensions across all pressure classes, see the complete ASME B16.5 reference tables.

Read the full guide to pipe flanges