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  • Concentric and Eccentric Reducers ASME B16.9 Dimensional Tolerances
June 7, 2025

Concentric and Eccentric Reducers ASME B16.9 Dimensional Tolerances

Concentric and Eccentric Reducers ASME B16.9 Dimensional Tolerances

by admin / Saturday, 28 December 2024 / Published in Pipe Fittings, Reducer
Concentric and Eccentric Reducer

Dimensional Tolerances of Concentric and Eccentric Reducers (ASME B16.9)

The ASME B16.9 standard specifies dimensional tolerances for factory-made wrought butt-welding fittings, including concentric and eccentric reducers. These tolerances ensure uniformity, accuracy, and compatibility across various piping systems. Below is a detailed breakdown of the tolerances applied to concentric and eccentric reducers as per ASME B16.9.


1. Dimensions and Terminology

Before diving into tolerances, it’s essential to understand the key dimensions of a reducer:

Dimension Description
D1 Outside diameter of the larger end of the reducer.
D2 Outside diameter of the smaller end of the reducer.
L End-to-end overall length of the reducer.
T Wall thickness of the reducer, which should match the pipe thickness (schedule).
Eccentricity For eccentric reducers, the vertical offset between the larger and smaller ends.

2. Dimensional Tolerances

The following table summarizes the key tolerances for concentric and eccentric reducers as specified by ASME B16.9:

Dimension Tolerance
Outside Diameter (D1 and D2) ±1% of the specified outside diameter or ±3.0 mm (whichever is smaller).
End-to-End Length (L) ±1.5% of the specified overall length or ±3.0 mm (whichever is smaller).
Wall Thickness (T) Must not be less than 87.5% of the nominal thickness specified (ASME B16.9 minimum wall rule).
Eccentricity Must not exceed the standard eccentricity value specified in the design (typically ±3.0 mm).

3. Detailed Explanation of Each Tolerance

A. Outside Diameter (D1 and D2)

The outer diameter of both ends of the reducer (D1 for the larger end and D2 for the smaller end) must be within ±1% of the nominal diameter specified or a maximum deviation of ±3.0 mm. This ensures a proper fit with adjoining pipes.

B. End-to-End Length (L)

The overall length (L) of the reducer is critical for alignment in piping systems. ASME B16.9 specifies that the tolerance for the length is ±1.5% or ±3.0 mm, whichever is smaller.

C. Wall Thickness (T)

  • The wall thickness of the reducer must adhere to the minimum wall rule specified by ASME B16.9.
  • A reducer’s wall thickness should not fall below 87.5% of the nominal thickness, ensuring structural integrity under pressure.

D. Eccentricity (Offset)

For eccentric reducers, the vertical offset between the centerlines of the large and small ends is referred to as eccentricity. The tolerance for this is typically limited to ±3.0 mm, ensuring that the offset remains within acceptable limits for proper flow alignment and drainage.


4. Inspection and Quality Control

The ASME B16.9 standard mandates stringent inspection protocols to ensure reducers meet the specified tolerances. Some of the common inspection methods include:

Inspection Method Purpose
Dimensional Inspection Verifies D1, D2, L, and eccentricity using calipers and micrometers.
Wall Thickness Measurement Ensures compliance with minimum wall thickness requirements.
Visual Inspection Checks for surface defects, such as cracks, dents, or corrosion.
Nondestructive Testing (NDT) Ultrasonic or radiographic tests ensure no internal flaws in seamless reducers.

5. Tolerance Table for Quick Reference

Below is a summarized table for quick reference:

Dimension Tolerance
D1 and D2 ±1% of nominal diameter or ±3.0 mm (whichever is smaller).
End-to-End Length ±1.5% of nominal length or ±3.0 mm (whichever is smaller).
Wall Thickness ≥87.5% of nominal thickness.
Eccentricity ±3.0 mm maximum.

6. Practical Implications of Tolerances in Piping Systems

Adherence to ASME B16.9 tolerances ensures:

  • Ease of Installation: Ensures seamless integration with pipes, valves, and other fittings.
  • Performance Integrity: Proper dimensional tolerances prevent leaks and ensure smooth flow.
  • Safety and Reliability: Ensures reducers can withstand operating pressures and temperatures.

NPS O.D.
D
O.D.
D1
Length
H
3/4 – 1/2 26.7 21.3 38
1 – 1/2 33.4 21.3 51
1 – 3/4 33.4 26.7 51
1.1/4 – 1/2 42.2 21.3 51
1.1/4 – 3/4 42.2 26.7 51
1.1/4 – 1 42.2 33.4 51
1.1/2 – 1/2 48.3 21.3 64
1.1/2 – 3/4 48.3 26.7 64
1.1/2 – 1 48.3 33.4 64
1.1/2 – 1.1/4 48.3 42.2 64
2 – 3/4 60.3 26.7 76
2 – 1 60.3 33.4 76
2 – 1.1/4 60.3 42.2 76
2 – 1.1/2 60.3 48.3 76
2.1/2 – 1 73 33.4 89
2.1/2 – 1.1/4 73 42.2 89
2.1/2 – 1.1/2 73 48.3 89
2.1/2 – 2 73 60.3 89
3 – 1.1/4 88.9 42.2 89
3 – 1.1/2 88.9 48.3 89
3 – 2 88.9 60.3 89
3 – 2.1/2 88.9 73 89
3.1/2 – 1.1/4 101.6 42.2 102
3.1/2 – 1.1/2 101.6 48.3 102
3.1/2 – 2 101.6 60.3 102
3.1/2 – 2.1/2 101.6 73 102
3.1/2 – 3 101.6 88.9 102
4 – 1.1/2 114.3 48.3 102
4 – 2 114.3 60.3 102
4 – 2.1/2 114.3 73 102
4 – 3 114.3 88.9 102
4 – 3.1/2 114.3 101.6 102
5 – 2 141.3 60.3 127
5 – 2.1/2 141.3 73 127
5 – 3 141.3 88.9 127
5 – 3.1/2 141.3 101.6 127
5 – 4 141.3 114.3 127
6 – 2.1/2 168.3 73 140
6 – 3 168.3 88.9 140
6 – 3.1/2 168.3 101.6 140
6 – 4 168.3 114.3 140
6 – 5 168.3 141.3 140
8 – 3.1/2 219.1 101.6 152
8 – 4 219.1 114.3 152
8 – 5 219.1 141.3 152
8 – 6 219.1 168.3 152
10 – 4 273 114.3 178
10 – 5 273 141.3 178
10 – 6 273 168.3 178
10 – 8 273 219.1 178
12 – 5 323.9 141.3 203
12 – 6 323.9 168.3 203
12 – 8 323.9 219.1 203
12 – 10 323.9 273 203
14 – 6 355.6 168.3 330
14 – 8 355.6 219.1 330
14 – 10 355.6 273 330
14 – 12 355.6 323.9 330
16 – 8 406.4 219 356
16 – 10 406.4 273 356
16 – 12 406.4 323.9 356
16 – 14 406.4 355.6 356
18 – 10 457 273 381
18 – 12 457 323.9 381
18 – 14 457 355.6 381
18 – 16 457 406.4 381
20 – 12 508 323.9 508
20 – 14 508 355.6 508
20 – 16 508 406.4 508
20 – 18 508 457 508
22 – 14 559 355.6 508
22 – 16 559 406.4 508
22 – 18 559 457 508
22 – 20 559 508 508
24 – 16 610 406.4 508
24 – 18 610 457 508
24 – 20 610 508 508
24 – 22 610 559 508
26 – 18 660 457 610
26 – 20 660 508 610
26 – 22 660 559 610
26 – 24 660 610 610
28 – 18 711 457 610
28 – 20 711 508 610
28 – 24 711 610 610
28 – 26 711 660 610
30 – 20 762 508 610
30 – 24 762 610 610
30 – 26 762 660 610
30 – 28 762 711 610
32 – 24 813 610 610
32 – 26 813 660 610
32 – 28 813 711 610
32 – 30 813 762 610
34 – 24 864 610 610
34 – 26 864 660 610
34 – 30 864 762 610
34 – 32 864 813 610
36 – 24 914 610 610
36 – 26 914 660 610
36 – 30 914 762 610
36 – 32 914 813 610
36 – 34 914 864 610
38 – 26 965 660 610
38 – 28 965 711 610
38 – 30 965 762 610
38 – 32 965 813 610
38 – 34 965 864 610
38 – 36 965 914 610
40 – 30 1016 762 610
40 – 32 1016 813 610
40 – 34 1016 864 610
40 – 36 1016 914 610
40 – 38 1016 965 610

Dimensions are in millimeters unless otherwise indicated. Wall thickness (t) must be specified by customer.

Concentric and Eccentric Reducer

 

Dimensional Tolerances of Concentric and Eccentric Reducers ASME B16.9

Nominal Pipe Size 1/2 to 2.1/2 3 to 3.1/2 4 5 to 8
Outside Diameter at Bevel (D) + 1.6
– 0.8
1.6 1.6 + 2.4
– 1.6
Inside Diameter at End 0.8 1.6 1.6 1.6
Overall Length (H) 2 2 2 2
Nominal Pipe Size 10 to 18 20 to 24 26 to 30 32 to 48
Outside Diameter at Bevel (D) + 4
– 3.2
+ 6.4
– 4.8
+ 6.4
– 4.8
+ 6.4
– 4.8
Inside Diameter at End 3.2 4.8 + 6.4
– 4.8
+ 6.4
– 4.8
Overall Length (H) 2 2 5 5
Wall Thickness (t) Not less than 87.5% of Nominal Wall Thickness

Dimensional tolerances are in millimeters unless otherwise indicated and are equal ± except as noted.

7. Conclusion

The dimensional tolerances outlined in ASME B16.9 for concentric and eccentric reducers are critical for maintaining the integrity and efficiency of piping systems. Whether it’s the wall thickness, end-to-end length, or eccentricity, these tolerances ensure that reducers meet performance expectations under various operating conditions.

To ensure compliance, always source reducers from reputable manufacturers who adhere to ASME standards and conduct thorough quality checks before installation.

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