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Weld Neck Flange Materials and Standards

asme b16 47 series b flange dimensions, weld neck flange materials
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A weld neck flange provides a strong and reliable piping connection, but only when the correct material specification and dimensional standard are used. A wrong grade or wrong series means the flange either fails in service or won’t bolt up at all. This guide covers the ASTM material grades used in weld neck flange manufacturing and the ANSI/ASME standards that govern their dimensions.

Material Grades

Weld neck flanges are forged, which limits the material options to grades suited to forging rather than plate fabrication. The two most common are ASTM A105 for carbon steel and ASTM A182 for stainless and low-alloy steel.

ASTM A105 — Carbon Steel

ASTM A105 is the standard specification for carbon steel forgings used in pressure piping. It covers flanges, fittings, valves, and similar forged components rated for ambient to moderately elevated temperature service, up to roughly 800°F (425°C) under ANSI/ASME B16.5 Group 1.1. A105 falls in the medium carbon range at 0.35% maximum carbon content. And it also contains small controlled additions of manganese and silicon, with only trace allowances for chromium, nickel, molybdenum, and copper. It is the default grade for weld neck flanges in general process piping, power piping, and water infrastructure.

ASME B16.47 Class 300, Class 300 Weld Neck Flange Dimensions

ASTM A182 — Stainless and Alloy Steel

ASTM A182 covers forged alloy and stainless steel pipe flanges, fittings, valves, and similar parts for high-temperature service. It includes the F-series alloy grades (F11, F22, F91) that are used for elevated-temperature process piping. It also includes the 300-series stainless grades (F304, F304L, F316, F316L) that have high corrosion resistance. Weld neck flanges in 304/304L or 316/316L stainless are specified for chemical processing, food and beverage, marine, and other corrosive or sanitary services where carbon steel is not suitable.

ANSI/ASME 16.47 class 150, Class 150 Weld Neck Flange Dimensions
GradeProduct FormTypical Service
ASTM A105Forged carbon steelGeneral process and power piping, ambient to 800°F
ASTM A182 F304/F304LForged stainless steelCorrosion resistance, moderate-temperature process piping
ASTM A182 F316/F316LForged stainless steelHigher corrosion resistance, chloride and marine environments
ASTM A182 F11, F22, F91Forged alloy steelHigh-temperature steam and process piping above carbon steel limits

For a full breakdown of alloy grade selection, see Alloy Steel vs Carbon Steel Flanges.

Dimensional Standards

The material grade determines what the flange is made of and the dimensional standards determine its size, drilling, and pressure rating. Weld neck flanges are covered primarily by two standards depending on size. ANSI/ASME B16.5 applies to flanges from NPS ½” through 24″, in pressure classes 150, 300, 400, 600, 900, 1500, and 2500. And  ANSI/ASME B16.47 covers larger sizes, NPS 26″ through 60″, divided into Series A and Series B, which are not interchangeable.

Standard

Size Range

Pressure Classes

ANSI/ASME B16.5

NPS ½” through 24″

150, 300, 400, 600, 900, 1500, 2500

ANSI/ASME B16.47 Series A

NPS 26″ through 60″

75, 150, 300, 400, 600, 900

ANSI/ASME B16.47 Series B

NPS 26″ through 60″

75, 150, 300, 400, 600, 900

Basic Weld Neck Flange Dimensions

Weld neck flange dimensions, outside diameter, flange thickness, hub diameter, bolt circle, and drilling, are set entirely by the governing standard and pressure class, not by material. As an example, the table below shows the full ANSI/ASME B16.5 Class 150 weld neck dimensions by nominal pipe size, as listed on our own dimension tables. The same drilling (bolt circle, bolt count, and bolt hole size) is shared across flange types at a given size and class. What changes between types is the hub and bore.
NPS O.D. Flange THK Hub Dia (X) Bolt Circle No. Bolts Bolt Hole Dia
½3.500.381.192.3840.630
¾3.880.441.502.7540.630
14.250.501.943.1340.630
1¼4.630.562.313.5040.630
1½5.000.622.563.8840.630
26.000.693.064.7540.750
2½7.000.813.565.5040.750
37.500.884.256.0040.750
3½8.500.884.817.0080.750
49.000.885.317.5080.750
510.000.886.448.5080.875
611.000.947.569.5080.875
813.501.069.6911.7580.875
1016.001.1212.0614.25121.000
1219.001.1914.3817.00121.000
1421.001.3115.7818.75121.125
1623.501.3818.0021.25161.125
1825.001.5019.8822.75161.250
2027.501.6222.0025.00201.250
2229.501.7524.0027.25201.375
2432.001.8126.1229.50201.375

All dimensions in inches, per ASME/ANSI B16.5 Table 8C, Class 150. The hub diameter at the weld end equals the outside diameter of the matching pipe; bore is specified by the purchaser. The same dimensions apply to carbon steel (ASTM A105) and stainless steel (ASTM A182, 304/304L or 316/316L). Full per-size tables are also available for Class 300 weld neck flanges.

NPS O.D. Flange THK Hub Dia (X) Bolt Circle No. Bolts Bolt Hole Dia
½ 3.50 0.38 1.19 2.38 4 0.630
¾ 3.88 0.44 1.50 2.75 4 0.630
1 4.25 0.50 1.94 3.13 4 0.630
1¼ 4.63 0.56 2.31 3.50 4 0.630
1½ 5.00 0.62 2.56 3.88 4 0.630
2 6.00 0.69 3.06 4.75 4 0.750
2½ 7.00 0.81 3.56 5.50 4 0.750
3 7.50 0.88 4.25 6.00 4 0.750
3½ 8.50 0.88 4.81 7.00 8 0.750
4 9.00 0.88 5.31 7.50 8 0.750
5 10.00 0.88 6.44 8.50 8 0.875
6 11.00 0.94 7.56 9.50 8 0.875
8 13.50 1.06 9.69 11.75 8 0.875
10 16.00 1.12 12.06 14.25 12 1.000
12 19.00 1.19 14.38 17.00 12 1.000
14 21.00 1.31 15.78 18.75 12 1.125
16 23.50 1.38 18.00 21.25 16 1.125
18 25.00 1.50 19.88 22.75 16 1.250
20 27.50 1.62 22.00 25.00 20 1.250
22 29.50 1.75 24.00 27.25 20 1.375
24 32.00 1.81 26.12 29.50 20 1.375
All dimensions in inches, per ASME/ANSI B16.5 Table 8C, Class 150. The hub diameter at the weld end equals the outside diameter of the matching pipe; bore is specified by the purchaser. The same dimensions apply to carbon steel (ASTM A105) and stainless steel (ASTM A182, 304/304L or 316/316L).
Full per-size tables are available for Class 150 and Class 300 weld neck flanges, both fully verified against our own dimension pages.

Certification and Traceability

Certified mill test reports (MTRs) document meets the chemical composition and mechanical property requirements of its ASTM grade. On code-governed projects, MTRs are a baseline requirement rather than an optional add-on, and are best requested at the time of order. For projects under Buy American or BABA provisions, domestically produced A105 and A182 material satisfies those requirements without the import documentation foreign material requires.

Weld Neck Flanges From API International

API International supplies weld neck flanges machined from A105 forged carbon steel and A182 and 304/316 forged stainless steel, meeting ANSI/ASME B16.5 and ANSI/ASME B16.47 standards. Explore our full range in the online product catalog, or contact us for custom machining. Get connected with a dedicated sales representative today, or call us at 503.692.3800.

Frequently Asked Questions

What material grade is used for standard weld neck flanges?
ASTM A105 is the standard carbon steel grade for weld neck flanges. ASTM A182 covers stainless and alloy steel versions, including F304/F304L and F316/F316L.

What is the difference between ANSI/ASME B16.5 and B16.47 for weld neck flanges?
ANSI/ASME B16.5 covers sizes NPS ½″ through 24″. ANSI/ASME B16.47 covers NPS 26″ through 60″, split into Series A and Series B, which use different dimensions and are not interchangeable.

Do weld neck flange dimensions change with material?
No. Outside diameter, bolt circle, and drilling are set by the dimensional standard and pressure class, and are identical whether the flange is carbon steel or stainless steel. Material affects corrosion resistance, temperature rating, and cost, not the dimensional layout.

What is the maximum temperature rating for an A105 weld neck flange?
Under ANSI/ASME B16.5 Group 1.1, A105 weld neck flanges are rated up to roughly 800°F (425°C). Above that range, alloy grades under ASTM A182 (such as F11 or F22) are required.

Are mill test reports required for weld neck flanges?
On code-governed or quality-controlled projects, yes. Certified MTRs confirm that the material meets the specified ASTM chemistry and mechanical requirements, and are best requested at the time of order.