Concentric and Eccentric Reducers ASME B16.9 Dimensional Tolerances

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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

 

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.