ASME B16.5 Flange and Flanged Fittings Specification

ASME B16.5 is the most common use standard specification for manufacturing cast and forged steel pipe flange and flanged fittings. 

Standard Scope

This standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flange and flanged fittings. ASME B16.5 standard covers Steel Pipe Flanges and Flanged Fittings from NPS 1/2 through NPS 24 Metric/Inch in pressure class 150 to class 2500. 

ASME B16.5 limited to:

  • Flanges and flanged fittings made from cast or forged materials
  • Blind flanges and certain reducing flanges made from cast, forged or plate materials.
  • Flange bolting, gaskets and joints.

Unit

Flanges with rating class of 150#, 300#, 400#, 600#, 900# and 1500# in sizes NPS 1/2 to 24. For 2500# in sizes from NPS 1/2 to NPS 12, with requirements in both metric and U.S. Customary units with diameter of bolts and flange bolt holes expressed in inch units.

Flanged fittings with 150#, 300# in sizes of NPS 1/2 to NPS 24, expressed in inch Units.

Flanged fittings with 400#, 600#, 900#, and 1500# from NPS 1/2 to NPS24, and 2500# from NPS 1/2 to NPS 12, which only US. Customary units are provided. More details visit Nonmandatory Appendix E in ASME B16.5.

ASME B16.5 Ratings Designation

Class, followed by a dimensionless number, is the designation for pressure-temperaure ratings as follows:

Class   150   300   400   600   900   1500   2500

Size

In NPS, is designation for nominal flange or flange fittings size. NPS related to nominal diameter, DN in international standards, relations as below:

NPS

DN

1/2

15

3/4

20

1

25

1 1/4

32

 1 1/2

40

2

50

2 1/2

65

3

80

4

100

Note: For NPS ≥ 4, the related DN = 25 multiplied by the NPS number. For example NPS 10 is DN250.


Pressure-Temperature Rating

The pressure-temperature rating is the maximum allowable working pressure (bar unit) of the material and grade used at the rated temperature (Celsius).

Flanged Joints

A flanged joint is composed of separate and independent, although interrelated components: the flanges, gasket, and bolting, which are assembled by another influence, the assembler. Proper controls must be exercised in the selection and application for all these elements to attain a joint that has acceptable leak tightness. Special techniques, such as controlled bolt tightening, are described in ASME PCC-1

Mixed Flanged Joints

If the flanges of a flange joint have different pressure-temperature ratings, the flange joint shall be rated for the lower of the two ratings at that temperature at any temperature.

Rated temperature

The rated temperature corresponding to the rated pressure is refers to the temperature of the pressure vessel of the flange and flange fittings. This temperature is generally the same as the temperature of the stored liquid.

Use of a pressure rating corresponding to a temperature other than that of the contained fluid is the responsibility of the user, subject to the requirements of applicable codes and regulations. For any temperature below−29°C (−20°F),the rating shall be no greater than the rating shown for −29°C(−20°F).

Temperature Consideration

Whether flange joints are used at high or low temperatures, leakage due to external forces and moments generated by the connected piping or equipment should be considered. To prevent leakage, pipe flanges and flanged fittings should avoid the application of severe external loads and sharp thermal gradients.

High Temperature

Application at temperatures in the creep range will result in decreasing bolt loads as relaxation of flanges, bolts, and gaskets takes place. Flanged joints subjected to thermal gradients may likewise be subject to decreasing bolt loads. Decreased bolt loads diminish the capacity of the flanged joint to sustain loads effectively without leakage. At temperatures above 200°C (400°F) for Class 150 and above 400°C (750°F) for other class designations, flanged joints may develop leakage problems unless care is taken to avoid imposing severe external loads, severe thermal gradients, or both.

Low Temperature

Some materials, especially some carbon steel materials, exhibit a significant decrease in ductility when used at low temperatures, and thus cannot withstand impact load, sudden stress changes, and high stress concentrations. Some regulations require an impact test even when the temperature is above -29 °C (−20°F).

System Hydrostatic Testing

Flanged joints and flanged fittings may be subjected to system hydrostatic tests at a pressure of 1.5 times the 38°C (100°F) rating rounded off to the next higher 1 bar (25 psi)
increment. Testing at any higher pressure is the responsibility of the user,taking into account the requirements of the applicable code or regulation.

Identification Markings

A ASME B16.5 flange shall furnished with below marking requirements. Flange and flange fittings shall be marked in accordance with MSS SP-25 except for modifications to this specification.

  • Name: Manufacturer name or trademark
  • Material: Cast or Forged, material standard ASTM xxx.
  • Pressure Ratings: Class 150 to 2500
  • Conformance: ASME B16.5 or other B16 standard.
  • Temperature
  • Size
  • Ring Joint Flanges: Shall be marked with letter R and ring groove number.
  • Multiple Material Marking: In case multiple material used.

Materials

Material required for flanges and flanged fittings commonly are:

  • ASTM A105 for forged carbon steel flange
  • ASTM A350 for forged carbon steel, low alloy steel flange
  • ASTM A182 for alloy steel flange and stainless steel flange
  • ASTM A216 for casting carbon steel flanges
  • ASTM A352, ASTM A217
  • ASTM A515 Gr 70, 65 for plates flange
  • ASTM A516 Gr 70, 65 for carbon and low alloy steel plates flange
  • ASTM A203, A204
  • ASTM A387 Gr 11, 22, 91 CL 2 for alloy steel plates flange
  • ASTM A240 Grade 304/L, 316/L for stainless steel plate flange

Notes:

(1) Plate and flat bar materials shall be used only for blind flanges and reducing flanges without hubs.

(2) Flanges and flanged fittings shall be manufactured as one piece in accordance with the applicable material specification. Assembly of multiple pieces into the finished product by welding or other means is not permitted by this Standard

Mechanical properties

The mechanical properties shall be determined from the specimen and the specimen shall represent the final heat treated condition of the material as required by the material standard.

Bolts

Include high strength bolts, medium strength bolts, low strength bolts and bolts for grey cast iron flanges.

Gasket

The material of the ring gasket shall comply with ASME B 16.20. The user is responsible for selecting gasket materials that are suitable for operating conditions, can withstand bolt loads, and do not cause cracking.

ASME B16.5 Flange Dimensions

ASME B16.5 flange dimensions including different pressure ratings for weld neck flange, slip on flange, blind flange, reducing flange, socket weld flange, threaded flange, view below for more details.

Class 150, 300, 600 Flange Dimensions

Tolerance

In order to determine compliance with this standard, where a fixed effective number is required where the limits, maximum and minimum values are specified, rounding shall be  in accordance with the method defined in ASTM Practice E29.

Required tolerances for different flanges and flanged fittings elements are as follows:

Center to Contract Surfaces and Center to End Tolerances

(a). Center-to-Contract Surfaces other than Ring Joint

Size

Tolerance

NPS ≤ 10

+/- 1.0 mm (+/- 0.03 in.)

NPS ≤ 12

+/- 1.5 mm (+/- 0.06 in.)

(b). Center-to-End (Ring Joint)

Size

Tolerance

NPS ≤ 10

+/- 1.0 mm (+/- 0.03 in.)

NPS ≤ 12

+/- 1.5 mm (+/- 0.06 in.)

(c). Center surface-to-Contact surface other than ring joint

Size

Tolerance

NPS ≤ 10

±2.0 mm(±0.06 in.)

NPS ≥ 12

±3.0 mm(±0.12 in.)

(d). End-to-End

Size

Tolerance

NPS ≤ 10

±2.0 mm(±0.06 in.)

NPS ≥ 12

±3.0 mm(±0.12 in.)

Tolerances for Flange Facings

For both flange and flanged fittings facings tolerances are as follows:

(a) Inside and outside diameter of large and small tongue and groove and female, ±0.5 mm (±0.02 in.).
(b) Outside diameter,2.0 mm (0.06 in.) raised face, ±1.0 mm (±0.03 in.).
(c) Outside diameter, 7.0 mm (0.25 in.) raised face, ±0.5 mm (±0.02 in.).
(d) Ring joint groove tolerances are shown in Table 5 (Table II-5 of Mandatory Appendix II in ASME B16.5)
(e)Perpendicularity of the face with the bore as below table

Size

Tolerance

NPS ≤ 5

1 deg

NPS ≥ 6

0.5 deg

Flange thickness tolerances

Size

Tolerance

NPS ≤ 18

+3.0, -0.0 mm (+0.12,-0.00 in.)

NPS ≥ 20

+5.0, -0.0 mm (+0.19,-0.00 in.)

The plus tolerance is applicable to bolting bearing surfaces whether as-forged, as-cast, spot-faced, or back-faced.

Welding end flange ends and hubs

Outside Diameter

For welding ends of welding neck flanges nominal outside diameter as follows:

Size

Tolerance

NPS ≤ 5

+2.0, -1.0 mm (+0.09,-0.03 in.)

NPS ≥ 6

+4.0, -1.0 mm (+0.16,-0.03 in.)

Inside Diameter

Tolerances for nominal inside diameter of welding ends of weld neck flange and socket weld flange with smaller bore.

(a) For figures 7 (Bevel for wall thickness  from 5 mm to 22 mm), figure 8 (greater than 22 mm) and figure 4 (Straight Hub Welding Flange) in ASME B16.5.

Size

Tolerance

NPS ≤ 10

±1.0 mm (±0.03 in.)

12 ≤ NPS ≤ 18

±1.5 mm (±0.06 in.)

NPS ≥ 20

+3.0, -1.5 mm (+0.12,-0.06 in.)

For figure 9 (Inside Contour for Use With Rectangular Backing Ring)

Size

Tolerance

NPS ≤ 10

+0.0, -1.0 mm (+0.0,-0.03 in.)

NPS ≥ 12

+0.0, -1.5 mm (+0.0,-0.06 in.)

Backing ring contact surface

Size

Tolerance

2 ≤ NPS ≤ 24

+0.25, -0.0 mm (+0.01,-0.0 in.)

Length through hub on welding neck flanges

Size

Tolerance

NPS ≤ 4

±1.5mm (±0.06 in.)

5 ≤ NPS ≤ 10

+1.5, -3.0 mm (+0.06,-0.12 in.)

NPS ≥ 12

+3.0, -5 mm (+0.12,-0.18 in.)

Flange Bore Diameter

Lapped and Slip-On Flange Bores

Size

Tolerance

NPS ≤ 10

+1.0, -0.0 mm (+0.03,-0.0 in.)

NPS ≥ 12

+1.5, -0.0 mm (+0.06,-0.0 in.)

Counter Bores, Threaded Flanges

Size

Tolerance

NPS ≤ 10

+1.0, -0.0 mm (+0.03,-0.0 in.)

NPS ≥ 12

+1.5, -0.0 mm (+0.06,-0.0 in.)

Counter Bores, Socket Welding Flanges

Size

Tolerance

1/2 ≤ NPS ≤ 3

±0.25 mm (±0.010 in.)

Pressure Test

No pressure test is required on the flange.

Flanged fitting should be tested for shell pressure. 

Shell Pressure Test for Flanged Fittings

The shell pressure test for flanged fittings shall be at a pressure no less than 1.5 times the 38°C (100°F) pressure rating rounded off to the next higher 1 bar (25 psi) increment.

Test Conditions

The shell pressure test for flanged fittings shall be at a pressure no less than 1.5 times the 38°C (100°F) pressure rating rounded off to the next higher 1 bar (25 psi) increment

Test Duration

Flanged Fittings Size

Duration, Sec

                              NPS ≤ 2

60

                           2 1/2 ≤ NPS ≤ 8

120

                              NPS ≥ 10

180