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ASME B16.5 is the most common use standard specification for manufacturing cast and forged steel pipe flange and flanged fittings.
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.
What does ASME B16 5 mean?
B16. 5 is limited to flanges and flanged fittings made from cast or forged materials, and blind flanges and certain reducing flanges made from cast, forged, or plate materials. Also included in this Standard are requirements and recommendations regarding flange bolting, flange gaskets, and flange joints.
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:
| Element | Composition, % Heat Analysis |
|---|---|
| Carbon, max | 0.3 |
| Manganese, max | 1.6 |
| Phosphorus, max | 0.025 |
| Sulfur, max | 0.025 |
| Silicon | 0.15-0.35 |
| Copper | |
| Nickel | |
| Chromium | |
| Molybdenum | |
| Vanadium | |
| Columbium (Niobium) | |
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.
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
- Ring Joint Facing Dimensions
- Class 150 Flange Dimensions
- Class 300 Flange Dimensions
- Class 600, 900, 1500, 2500 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 |
What is the difference between ASME B16.5, ASME B16.47 Series A, Series B and API 605 Flanges
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. It covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings. Two very important flanges such as weld neck flange and blind flanges are very commonly used in piping systems. The term “B16.5” or “B16 5” is used interchangeability and refers to same standard. However, the standard ASME B16 5 (ANSI B16 5) only covers size up to 24 inches. For bigger sizes, ASME B16.47 standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for pipe flanges in sizes NPS 26 through NPS 60 and in ratings Classes 75, 150, 300, 400, 600, and 900.
However, the standard ASME B16.47 is further divided into ASME B16.47 series A and ASME B16.47 series B flange for Blind flange and Weldneck flange. Series B flange was also formerly known as API 605 flange. Term B16.47 or B 16 47 or ANSI B 16 47 are all used interchangeabily and refers to the same standard.
ASME B16.47(Large Diameter Steel Flanges) is a standard for large diameter steel pipe flanges sized from NPS 26 through NPS 60. The latest version provides dimensions and ratings in both metric and inch units. The ASME B16.47 incorporate MSS SP-44: Steel Pipeline Flanges and API 605: Large Diameter Carbon Steel Flanges. Therefore, the MSS SP-44 flanges are designated as ASME B16.47 Series A flanges, while API 605 flanges are designated as ASME B16.47 Series B flanges within this standard. Materials covered in this standard are as that in ASME B16.5 except for nickel alloys which means they share the same pressure-temperature chart for the selection of flange materials.
So what is the difference between ASME B16.47 Series A and Series B (API605) flanges?
Generally speaking, ASME B16 47 Series A flanges are much thicker, heavier and stronger than Series B flanges in the same size and pressure rating thus can withstand more external loading than Series B type. ASME B16.47 Series B flanges need more but smaller fasteners (bolts & nuts) than Series A flanges and have a smaller bolt circle diameter than that of Series A flanges. The smaller bolt circle diameter results in less flange movement after installation. Both Series A and Series B standards define weld neck flanges and blind flanges in raised face type (RF) but only Series A defines ring type joint (RTJ) flanges from Class 300 through Class 900 within this standard. From a commercial point of view, ASME B16.47 Series A flanges are more expensive than ASME B16 47 Series B flanges.
Most piping users or designers may choose Series A flanges for the new pipeline or equipment. But if you are doing some refurbishment, replacement job or non-critical piping design, Series B flanges are more popular.
Conclusions: Standard weld neck, slip on, blind etc. flanges are covered by standard B16.5 for sizes up to 24″ nominal pipe. Sizes 26″ and bigger are covered by B16.47 series A or series B for weldneck and blind flanges. Series A flange is heavier, thicker and cost more whereas series B flange has more bolt holes and is lighter cheaper than series A. API605 flange and series B flanges are same thing.
