1. Scope

ASME B16.9 covers overall dimensions, tolerances, ratings, testing and marking for factory-made wrought buttwelding fittings in sizes NPS 1/2 through NPS 48 (DN 15 through DN 1200), in any producible wall thickness. It is a dimensional manufacturing standard: the geometry, tolerances and marking are fixed by B16.9, while the material is specified separately on the purchase order (ASTM A234, A403, A815, A420, A860, B366 and equivalent). The same centre-to-end dimensions apply whatever the material.

Elbows 90° and 45°, long radius (LR, R = 1.5×NPS) and short radius (SR, R = 1.0×NPS)
Tees and crosses equal and reducing
Reducers concentric and eccentric
Caps buttweld caps
Returns 180° returns, long radius and short radius
Edition referenced here ASME B16.9-2024
Governing code ASME BPVC Section II; ASME B31.1 / B31.3 for installation

2. Dimensional Letter Designations

Every dimension in this page is referred to by the letter used in the ASME B16.9 tables. The letters are fixed for each fitting type; the figures below show where each one is measured.

Letter	Applies to	Definition
A	90° elbows	Centre-to-end distance (for a 90° elbow this equals the bend radius R)
B	45° elbows	Centre-to-end distance
C	Tees and crosses	Run centre-to-end
M	Tees and crosses	Outlet (branch) centre-to-end
H	Reducers	Overall length (end to end)
E	Caps	Overall height (base to crown)
O	180° returns	Centre-to-centre of the two ends
K	180° returns	Back-to-face
D	All fittings	Outside diameter at bevel (equals the matching pipe OD)

3. 90° Elbows — Centre-to-End (A)

Figure 1 — 90° elbow. A is measured from the intersection of the two centre lines to the end face. LR: A = 1.5 × NPS. SR: A = 1.0 × NPS.

The long radius 90° elbow has a bend radius of 1.5 × NPS, the short radius elbow 1.0 × NPS. Because the standard sets a practical minimum, NPS 1/2, 3/4 and 1 all take A = 38 mm — 1.5 × NPS would give 19 mm and 28.5 mm for the two smallest sizes. Short radius elbows start at NPS 1; NPS 1/2 and 3/4 are not tabulated and are shown as a dash below.

NPS	DN	LR 90° — A (mm)	SR 90° — A (mm)
1/2	15	38	—
3/4	20	38	—
1	25	38	25
1-1/4	32	48	32
1-1/2	40	57	38
2	50	76	51
2-1/2	65	95	64
3	80	114	76
3-1/2	90	133	89
4	100	152	102
5	125	190	127
6	150	229	152
8	200	305	203
10	250	381	254
12	300	457	305
14	350	533	356
16	400	610	406
18	450	686	457
20	500	762	508
22	550	838	559
24	600	914	610
26	650	991	—
28	700	1067	—
30	750	1143	—
32	800	1219	—
34	850	1295	—
36	900	1372	—
38	950	1448	—
40	1000	1524	—
42	1050	1600	—
44	1100	1676	—
46	1150	1753	—
48	1200	1829	—

ASME B16.9 also tabulates NPS 22 (DN 550), shown above. LR elbows extend to NPS 48; SR elbows are listed only to NPS 24.

4. 45° Elbows — Centre-to-End (B)

Figure 2 — 45° elbow. B is measured from the intersection of the centre lines to each end face. B = R × tan(22.5°) = 0.625 × NPS for the long radius series.

Long radius 45° elbows follow B = 0.625 × NPS from NPS 1/2 upward, with the same minimum effect at the small end (NPS 1/2 = 16 mm). The fitting is a pure 45° arc with no straight tangent length, which is why B is slightly less than half of A for the same size.

NPS	DN	LR 45° — B (mm)
1/2	15	16
3/4	20	19
1	25	22
1-1/4	32	25
1-1/2	40	29
2	50	35
2-1/2	65	44
3	80	51
3-1/2	90	57
4	100	64
5	125	79
6	150	95
8	200	127
10	250	159
12	300	190
14	350	222
16	400	254
18	450	286
20	500	318
22	550	349
24	600	381
26	650	413
28	700	445
30	750	476
32	800	508
34	850	540
36	900	572
38	950	603
40	1000	635
42	1050	667
44	1100	699
46	1150	730
48	1200	762

5. Tees and Crosses — Run (C) and Outlet (M)

Figure 3 — Tee. C is the run centre-to-end, M the outlet centre-to-end, both measured from the intersection of the run and branch centre lines. For an equal tee C = M.

For an equal tee the run and outlet dimensions are identical (C = M). For a reducing tee C is taken from the run size and M from the outlet size, so the two values differ. Values below are for the equal tee; for a reducing tee read C from the run row and M from the outlet row.

NPS	DN	C = M (mm)
1/2	15	25
3/4	20	29
1	25	38
1-1/4	32	48
1-1/2	40	57
2	50	64
2-1/2	65	76
3	80	86
3-1/2	90	95
4	100	105
5	125	124
6	150	143
8	200	178
10	250	216
12	300	254
14	350	279
16	400	305
18	450	343
20	500	381
22	550	406
24	600	432
26	650	457
28	700	495
30	750	533
32	800	559
34	850	610
36	900	648
38	950	686
40	1000	724
42	1050	762
44	1100	800
46	1150	838
48	1200	876

6. Reducers — Overall Length (H)

Figure 4 — Concentric and eccentric reducer. H is the end-to-end length and depends only on the NPS of the large end, not on the amount of reduction.

H is governed by the large end only. A 6×4 and a 6×2 concentric reducer have the same overall length. The series is not smooth: it holds at 203 mm from 12×10 through 12×8 and then jumps to 330 mm at 14×12, because the large-end NPS has moved from 12 to 14. Eccentric reducers use exactly the same H values.

Large end NPS	DN	H (mm)
3/4	20	38
1	25	51
1-1/4	32	51
1-1/2	40	64
2	50	76
2-1/2	65	89
3	80	89
3-1/2	90	102
4	100	102
5	125	127
6	150	140
8	200	152
10	250	178
12	300	203
14	350	330
16	400	356
18	450	381
20	500	508
22	550	508
24	600	508
26	650	559
28	700	610
30	750	660
32	800	711
34	850	762
36	900	813
38	950	864
40	1000	914
42	1050	965
44	1100	1016
46	1150	1067
48	1200	1118

7. Caps — Overall Height (E)

Figure 5 — Buttweld cap. E is the overall height measured from the open-end face to the crown.

E is the only dimensional envelope B16.9 fixes for a cap. The crown profile itself (ellipsoidal or hemispherical) is left to the manufacturer, so caps from different mills are interchangeable on E and on the bevel end, not necessarily on the internal shape.

NPS	DN	E (mm)
1/2	15	25
3/4	20	25
1	25	38
1-1/4	32	38
1-1/2	40	38
2	50	38
2-1/2	65	38
3	80	51
3-1/2	90	64
4	100	64
5	125	76
6	150	89
8	200	102
10	250	127
12	300	152
14	350	165
16	400	178
18	450	203
20	500	229
22	550	254
24	600	267
26	650	267
28	700	267
30	750	267
32	800	267
34	850	267
36	900	267
38	950	305
40	1000	305
42	1050	305
44	1100	343
46	1150	343
48	1200	343

8. 180° Returns — Centre-to-Centre (O) and Back-to-Face (K)

Figure 6 — 180° return. O is the distance between the two end centre lines; K is measured from the back of the bend to the plane of the two end faces.

A 180° return is dimensioned by O (centre-to-centre) and K (back-to-face). Two relationships are worth remembering:

O = 2 × A. The return is geometrically two 90° elbows back to back.
K cannot be derived for production. K = A + OD/2 applies to the long radius series, but the standard tables K directly and the published values, not a formula, govern acceptance.

8.1 Long Radius Returns

NPS	DN	OD at bevel (mm)	O (mm)	K (mm)
1/2	15	21.3	76	48
3/4	20	26.7	76	51
1	25	33.4	76	56
1-1/4	32	42.2	95	70
1-1/2	40	48.3	114	83
2	50	60.3	152	106
2-1/2	65	73.0	190	132
3	80	88.9	229	159
3-1/2	90	101.6	267	184
4	100	114.3	305	210
5	125	141.3	381	262
6	150	168.3	457	313
8	200	219.1	610	414
10	250	273.0	762	518
12	300	323.8	914	619
14	350	355.6	1067	711
16	400	406.4	1219	813
18	450	457.0	1372	914
20	500	508.0	1524	1016
22	550	559.0	1676	1118
24	600	610.0	1829	1219
26	650	660.0	1981	1321
28	700	711.0	2134	1422
30	750	762.0	2286	1524
32	800	813.0	2438	1626
34	850	864.0	2591	1727
36	900	914.0	2743	1829
38	950	965.0	2896	1930
40	1000	1016.0	3048	2032
42	1050	1067.0	3200	2134
44	1100	1118.0	3353	2235
46	1150	1168.0	3505	2337
48	1200	1219.0	3658	2438

8.2 Short Radius Returns

Short radius returns are listed only to NPS 24 (ASME B16.9 upper limit for SR fittings).

NPS	DN	OD at bevel (mm)	O (mm)	K (mm)
1	25	33.4	51	41
1-1/4	32	42.2	64	52
1-1/2	40	48.3	76	62
2	50	60.3	102	81
2-1/2	65	73.0	127	100
3	80	88.9	152	121
3-1/2	90	101.6	178	140
4	100	114.3	203	159
5	125	141.3	254	197
6	150	168.3	305	237
8	200	219.1	406	313
10	250	273.0	508	391
12	300	323.8	610	467
14	350	355.6	711	533
16	400	406.4	813	610
18	450	457.0	914	686
20	500	508.0	1016	762
22	550	559.0	1118	838
24	600	610.0	1219	914

9. Pipe Schedule and End-Wall Thickness

Schedule does not change any of the centre-to-end dimensions on this page. It changes only the wall thickness at the ends and, therefore, the weight of the fitting. The wall at the bevel end matches the nominal wall of the corresponding pipe; the body of the fitting may be thicker, which is why B16.9 fittings are usually stronger than the pipe they join.

NPS range	Schedules normally available	How the fitting is designated
NPS 1/2 – 10	STD (Sch 40), XS (Sch 80)	By weight: STD or XS
NPS 12 and above	Sch 10, 20, 30, 40, 60, 80, 100, 120, 140, 160	By schedule number
All sizes	The inside diameter and the nominal wall at the ends are specified by the purchaser	Wall thickness at the end is not less than 87.5% of nominal unless the purchaser specifies otherwise

10. End Preparation (Bevel)

Figure 7 — Buttwelding end preparation. Bevel angle 37.5° ± 2.5° with a 1.6 mm ± 0.8 mm land, per ASME B16.25.

B16.9 does not itself define the bevel. It requires ends suitable for butt welding and refers to ASME B16.25 for the geometry. The bevel angle is 37.5° ± 2.5° with a root face (land) of 1.6 mm ± 0.8 mm — a 75° included angle, not 30°.

Parameter	Requirement
Bevel angle	37.5° ± 2.5° from the radial plane (75° included angle)
Root face (land)	1.6 mm ± 0.8 mm (1/16 in ± 1/32 in)
Bore at the end	Matches the nominal bore of the corresponding pipe schedule
Wall thickness at the end	Not less than 87.5% of nominal unless otherwise specified
Compound bevel	Required where the wall thickness exceeds 22 mm. The compound geometry is defined in ASME B16.25, not in B16.9
End squareness	Per ASME B16.25; checked against the end face, not the bevel face

11. Tolerances

Tolerances are equal plus and minus unless noted. Values are from ASME B16.9 Table 12.

Dimension	NPS 1/2 – 24	NPS 26 – 30	NPS 32 – 48
Outside diameter at bevel, D 1/2–2-1/2: +1.6/−0.8  |  3–4: ±1.6  |  5–8: +2.4/−1.6  |  10–18: +4.0/−3.2  |  20–24: +6.4/−4.8	—	+6.4 / −4.8	+6.4 / −4.8
Centre-to-end A, B, C, M	±2	±3	±5
Overall length of reducers, H	±2	±5	±5
Overall height of caps, E	±3 (1/2–4)  |  ±6 (5–24)	±10	±10
180° return O, centre-to-centre	±6 (1/2–8)  |  ±10 (10–24)	—	—
180° return K, back-to-face	±6	—	—
Alignment of ends U (returns)	±1 (1/2–8)  |  ±2 (10–24)	—	—
Angularity, off angle Q / off plane P	±1 / ±2 (1/2–4)  |  ±2 / ±4 (5–8)  |  ±3 / ±5 (10–12)  |  ±3 / ±6 (14–16)  |  ±4 / ±10 (18–24)	±5 / ±10	±5 / ±13 / ±19

12. Pressure–Temperature Rating

ASME B16.9 fittings have no independent pressure–temperature rating. The rating of a butt-welded joint is established by the rating of the matching pipe, and, where a flange is involved, by the rating of the mating ASME B16.5 flange. In practice a B16.9 fitting on a Schedule 40 pipe carries the same pressure–temperature envelope as that pipe.

Matching pipe Rating follows the pipe specification and schedule (ASME B36.10M / B36.19M).
Flanged ends Rating equals the ASME B16.5 class rating of the mating flange.
Hydrostatic test Applied to the assembled system, normally at 1.5 × design pressure at ambient temperature. B16.9 does not require each fitting to be pressure tested.

13. Marking Requirements

Marking element	Example
Manufacturer name or trademark	HT PIPE
Material designation	WPB (per ASTM A234 / ASME SA-234)
Nominal size	NPS 6
Schedule or weight	STD, XS or Sch 40
Compliance marking	B16.9
Heat number or batch traceability	Heat No. / Batch No.

14. ASME B16.28 — Withdrawn, Content Now in B16.9

Full short radius data is given in sections 3 and 8.2 of this page.

15. Comparison with Related Fitting Standards

Standard	Size range	Scope and key distinction
ASME B16.9	NPS 1/2 – 48	General-purpose LR and SR elbows, tees, crosses, reducers, caps and returns. The base dimensional standard for all butt-welding fittings, all materials.
ASME B16.28	NPS 1/2 – 24 (withdrawn)	Short radius elbows and returns. Withdrawn 2024-08-31 and merged into B16.9.
ASME B16.49	NPS 4 – 48	Factory-made induction bends for pipeline service. Continuous arc, not a discrete fitting.
MSS SP-43	NPS 1/2 – 24	Light-wall corrosion-resistant (stainless) butt-welding fittings, schedules 5S and 10S. A simplified alternative to B16.9 for stainless; dimensions are not identical to B16.9.
MSS SP-75	NPS 2 – 60	High-strength ferritic (WPHY 42–70) fittings for pipeline service. Shorter than B16.9 fittings and not dimensionally interchangeable with them.
ASME B16.25	Referenced by B16.9	Buttwelding ends: bevel geometry, land and compound bevels.

16. Related Standards

Standard	Title
ASME B16.5	Pipe Flanges and Flanged Fittings (pressure–temperature ratings for flanged joints)
ASME B16.25	Buttwelding Ends
ASME B16.47	Large Diameter Steel Flanges NPS 26 through NPS 60
ASME B16.49	Factory-Made Wrought Steel Buttwelding Induction Bends
ASME B36.10M	Welded and Seamless Wrought Steel Pipe
ASME B36.19M	Stainless Steel Pipe
ASME B31.1 / B31.3	Power Piping / Process Piping (installation, weld and NDT requirements)
ASTM A234 / SA-234	Pipe Fittings of Wrought Carbon Steel and Alloy Steel
ASTM A403 / SA-403	Wrought Austenitic Stainless Steel Piping Fittings
ASTM A420 / SA-420	Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service
ASTM A815	Wrought Ferritic, Ferritic/Austenitic and Martensitic Stainless Steel Piping Fittings
ASTM A860	Wrought High-Strength Ferritic Steel Butt-Welding Fittings
ASTM B366	Factory-Made Wrought Nickel and Nickel Alloy Fittings
MSS SP-25	Standard Marking System for Valves, Fittings, Flanges and Unions

17. How to Order

Order element	Specify	Example
Standard	ASME B16.9	B16.9
Fitting type	Elbow, tee, cross, reducer, cap, return	Elbow
Radius	LR (1.5D) or SR (1.0D)	LR
Size	NPS	NPS 6
Schedule or weight	Schedule number or STD / XS	Sch 40
Material grade	Per purchase order	ASTM A234 WPB
Ends	Beveled (standard). Threaded ends are not covered by B16.9	Beveled
Quantity	Number of pieces	20
Inspection	Third-party inspection and certificate type if required	EN 10204 3.1 MTC

18. FAQ — Frequently Asked Questions

What is the difference between a long radius and a short radius elbow?

A long radius (LR) 90° elbow has a bend radius of 1.5 × NPS, a short radius (SR) elbow 1.0 × NPS. For NPS 10 the centre-to-end dimension is 381 mm for LR and 254 mm for SR. LR is the default in process piping because the gentler turn reduces pressure drop and turbulence; SR is used where the layout is tight.

Are short radius elbows still covered by ASME B16.28?

No. ASME B16.28-1994 was withdrawn on 2024-08-31 and its content moved into ASME B16.9, which now tabulates short radius elbows (NPS 1 through 24) and short radius returns (NPS 1 through 24). Cite B16.9.

Why do NPS 1/2, 3/4 and 1 long radius elbows all have A = 38 mm?

Because 1.5 × NPS would give 19 mm for NPS 1/2 and 28.5 mm for NPS 3/4, which is below the minimum that can be formed and welded reliably. ASME B16.9 sets 38 mm as the floor, so the three smallest sizes share the same value.

Does the pipe schedule change the centre-to-end dimension of a fitting?

No. Centre-to-end values for A, B, C and M are independent of schedule. Schedule affects only end-wall thickness and weight. A Sch 40 and a Sch 80 NPS 6 elbow have the same A.

Can I calculate K of a 180° return instead of looking it up?

Do not. K (back-to-face) is tabulated in ASME B16.9 because the crown of the bend is not a perfect arc once wall thinning and forming tolerances are taken into account. For the long radius series the tabulated values happen to track A + OD/2, but the table is what governs.

What is the difference between a concentric and an eccentric reducer?

A concentric reducer keeps both ends on the same centre line. An eccentric reducer offsets the small end so that one side stays flat; it is used in horizontal lines to avoid trapping gas at the top or to keep the bottom of the pipe clear for drainage. Overall length H is identical for both types at the same large-end size.

Do ASME B16.9 fittings carry a pressure rating of their own?

No. The rating comes from the matching pipe and, where a flange is used, from the ASME B16.5 class rating of that flange. Hydrostatic testing is performed on the assembled system, normally at 1.5 × design pressure, not on each individual fitting.

Which material specification applies to a B16.9 fitting?

B16.9 fixes dimensions only. The material is called out separately: ASTM A234 for carbon and alloy steel, A420 for low-temperature carbon steel, A403 for austenitic stainless, A815 for duplex and ferritic stainless, A860 for high-strength pipeline grades, and B366 for nickel alloys. A duplex fitting is therefore ordered as "NPS 6 LR elbow, ASME B16.9, ASTM A815 UNS S31803".

Are MSS SP-75 fittings interchangeable with ASME B16.9 fittings?

No. MSS SP-75 has its own tables and its fittings are shorter than the B16.9 equivalents, to save weight in pipeline service. Always state the standard on the purchase order; the two families cannot be mixed in the same spool without checking.