1. Scope
This standard covers factory-made wrought buttwelding short-radius fittings in carbon steel and alloy steel — in sizes NPS 1/2 through NPS 24. ASME B16.28 is a dimensional manufacturing standard; the geometry and tolerances apply to carbon and alloy steel grades only. The fitting material is specified per ASTM A234 (carbon/ferritic alloy: WPB, WPC, WP11, WP22, WP91) or ASTM A420 (low-temperature carbon steel). ASME B16.28 supplements ASME B16.9 for SR fittings NPS greater than 10 (B16.9 only lists SR up to NPS 10).
- Short Radius 90° Elbows (1.0D): centre-to-end dimension = 1.0 × OD (tighter than LR 1.5D per B16.9)
- Short Radius 180° Return Bends: centreline returns 180° to the same axis as inlet; both ends on the same centreline
Edition: ASME B16.28-1994 | Governing Code: ASME BPVC Section II | Nature: Dimensional manufacturing standard — carbon and alloy steel only (not all materials) | Relationship: B16.28 supplements ASME B16.9 for SR fittings NPS greater than 10 | Note: ASME B16.28 has not been revised since 1994. For stainless steel SR elbows, consult MSS SP-43 or ASME B16.9; for nickel alloy, contact the manufacturer.
2. SR 90° Elbow — Center-to-End Dimension (A)
| NPS |
DN |
Outside Diameter OD (mm) |
Center-to-End A = 1.0D (mm) |
Overall Height H ≈ 2A + OD (mm) |
| 1/2 |
15 |
21.3 |
21 |
63 |
| 3/4 |
20 |
26.7 |
27 |
79 |
| 1 |
25 |
33.4 |
33 |
102 |
| 1-1/2 |
40 |
48.3 |
48 |
152 |
| 2 |
50 |
60.3 |
60 |
191 |
| 3 |
80 |
88.9 |
89 |
279 |
| 4 |
100 |
114.3 |
114 |
362 |
| 6 |
150 |
168.3 |
168 |
533 |
| 8 |
200 |
219.1 |
219 |
698 |
| 10 |
250 |
273.0 |
273 |
872 |
| 12 |
300 |
323.9 |
324 |
1034 |
| 16 |
400 |
406.4 |
406 |
1305 |
| 20 |
500 |
508.0 |
508 |
1634 |
| 24 |
600 |
610.0 |
610 |
1963 |
3. SR 180° Return Bend — Dimensions
| NPS |
DN |
Center-to-End A (mm) |
Centerline-to-Centerline CL (mm) |
Outside Face-to-Outside Face F (mm) |
| 1 |
25 |
33 |
67 |
76 |
| 2 |
50 |
60 |
124 |
140 |
| 3 |
80 |
89 |
184 |
208 |
| 4 |
100 |
114 |
237 |
267 |
| 6 |
150 |
168 |
349 |
394 |
| 8 |
200 |
219 |
457 |
518 |
| 10 |
250 |
273 |
572 |
648 |
| 12 |
300 |
324 |
683 |
775 |
Note: 180° return bends per ASME B16.28 are available for NPS 1/2 through NPS 12. For larger sizes, consult the manufacturer.
4. Schedule-to-Wall Thickness (End Preparation)
| NPS Range |
Available Schedules |
Designation Method |
| NPS 1/2 – 10 |
STD (Schedule 40) and XS (Schedule 80) |
Weight designation |
| NPS 12 and above |
Sch 10, 20, 30, 40, 60, 80, 100, 120, 140, 160 |
Schedule number |
5. End Preparation (Beveling)
| Parameter |
Requirement |
| Bevel angle |
30° +0°/−5° from pipe axis |
| Tolerance land |
1.6 mm ±0.8 mm (1/16 in ±1/32 in) |
| End squareness tolerance |
0.06 mm per mm of diameter (max) |
| Governing standard |
ASME B16.25 |
6. Tolerances (Summary)
| Dimensional Parameter |
Tolerance |
| Center-to-end A (NPS ≤ 12) |
±1.5 mm |
| Center-to-end A (NPS > 12) |
±3.0 mm |
| Outside diameter at bevel |
±1% of OD (min 0.8 mm) |
| Wall thickness at ends |
Not less than minimum; not more than 1.14 × specified minimum |
| Centreline-to-centreline (return bends) |
±3.0 mm |
7. Common Material Grades for B16.28 Fittings
ASME B16.28 is a dimensional standard — the same dimensions apply regardless of material. The material grade is specified on the purchase order. Common material specifications include:
| Material Grade |
ASTM Spec |
Yield (MPa) |
Tensile (MPa) |
Category |
| WPB |
A234 |
240 |
415-585 |
Carbon steel |
| WPC |
A234 |
260 |
485-620 |
Carbon steel |
| WP11 (1.25Cr-0.5Mo-Si) |
A234 |
205 |
415-585 |
Alloy steel |
| WP22 Cl.1 (2.25Cr-1Mo) |
A234 |
205 |
415-585 |
Alloy steel |
| WP91 (9Cr-1Mo-V) |
A234 |
440 |
620-760 |
Alloy steel |
Note: ASME B16.28-1994 scope is limited to carbon steel and alloy steel only. Stainless steel (ASTM A403/A815) and nickel alloy (ASTM B366) SR fittings are outside the scope of B16.28. For stainless steel SR elbows, consult MSS SP-43 or ASME B16.9; for nickel alloy SR fittings, contact the manufacturer for dimensions.
8. LR vs SR Elbow Comparison (B16.28 vs B16.9)
| Parameter |
Long Radius (1.5D) — ASME B16.9 |
Short Radius (1.0D) — B16.28 / B16.9 |
| Centre-to-end A |
1.5 × OD |
1.0 × OD |
| Pressure loss coefficient K (approx.) |
0.3–0.4 |
0.9–1.0 |
| Available size range |
NPS 1/2 – 48 |
NPS 1/2 – 10 (B16.9); NPS 1/2 – 24 (B16.28) |
| Flow regime suitability |
All flow conditions; preferred for process piping |
Low-pressure, low-velocity, space-constrained applications |
| Erosion concern at high velocity |
Lower risk (gentler direction change) |
Higher risk — sharp direction change accelerates inner-arc erosion |
9. Related Standards
| Standard |
Title |
| ASME B16.9 |
Factory-Made Wrought Buttwelding Fittings (LR fittings, larger SR range via B16.28 supplement) |
| ASME B16.25 |
Buttwelding Ends (bevel and end preparation) |
| ASME B16.49 |
Factory-Made Wrought Steel Buttwelding Induction Bends |
| ASME SA-234 |
Pipe Fittings of Wrought Carbon Steel and Alloy Steel |
| ASME B36.10M |
Welded and Seamless Wrought Steel Pipe |
| MSS SP-43 |
Wrought Stainless Steel Buttwelding Fittings |
| MSS SP-75 |
Wrought High-Strength Ferritic Steel Buttwelding Fittings |
| MSS SP-25 |
Standard Marking System for Valves, Fittings, Flanges and Unions |
10. How to Order (Per ASME B16.28)
| Order Element |
Specification |
Example |
| Standard |
ASME B16.28 |
B16.28 |
| Fitting type |
SR 90° Elbow / SR 180° Return Bend |
SR 90° Elbow |
| Radius |
1.0D (Short Radius — mandatory for this standard) |
1.0D |
| Size |
NPS |
8 |
| Schedule / Weight |
Schedule number or STD/XS |
STD |
| Material grade |
Per purchase order (SA-234 WPB etc.) |
WPB |
| Ends |
Beveled (standard) |
Beveled |
| Quantity |
Number of pieces |
30 |
| Material test report |
EN 10204 3.1 MTC if required |
3.1 MTC |
11. FAQ — Frequently Asked Questions
| Question |
Answer |
| When should SR (1.0D) elbows be preferred over LR (1.5D)? |
SR elbows are preferred where space is severely constrained, in low-pressure utility systems, drain/vent lines, and wherever the pressure loss penalty of the SR elbow is acceptable. They should not be used in high-pressure process lines with high flow velocities (risk of erosion at the inner arc), in systems requiring minimal pressure drop, or in lines where frequent start-stop cycling causes fatigue loading — the tighter radius concentrates stress. |
| Are 180° return bends per B16.28 the same as return bends in ASME B16.9? |
No. ASME B16.9 return bends are only available in long radius (LR = 1.5D) configuration and are listed only up to NPS 12. ASME B16.28 covers short radius (1.0D) return bends for NPS 1/2 through NPS 12, providing a more compact option. The B16.28 return bend has a centreline span approximately 40% shorter than the B16.9 LR return bend for the same NPS. |
| Can B16.28 SR fittings be used with stainless steel pipe? |
Technically, the B16.28 dimensions could be used as a reference, but ASME B16.28-1994 scope is limited to carbon steel and alloy steel only — stainless steel SR fittings are outside its scope. For stainless steel piping systems, MSS SP-43 is the applicable standard for Schedule 5S/10S stainless fittings; ASME B16.9 provides SR elbows for NPS 1/2–10 in all stainless grades. For stainless steel NPS > 10 SR elbows, contact the fitting manufacturer to agree on dimensions. Stainless steel chemical compositions differ significantly from carbon steel, requiring separate NDE and corrosion-resistance verification. |
| What is the erosion risk with SR elbows at high flow velocities? |
SR elbows have a sharper inner arc than LR elbows, causing the flow to change direction more abruptly. At velocities above approximately 10 m/s for water or 30 m/s for gases, this creates elevated shear stress at the inner arc wall, accelerating erosion-corrosion — particularly critical in two-phase (liquid + gas) flow. For high-velocity single-phase flow in carbon steel, limit SR elbow velocity to below erosion velocity thresholds per ASME B31.3 Chapter VI. |
| What is the marking requirement for ASME B16.28 fittings? |
Per MSS SP-25 (Standard Marking System for Valves, Fittings, Flanges and Unions), each fitting must be marked with: manufacturer name/trademark, material designation (e.g., WPB), size (NPS), schedule, standard designation (B16.28), and heat/trace number. For smaller fittings (NPS < 1), abbreviated marking may be used. Marking must be permanent (die-stamped, stenciled, or etched) and legible after any final surface treatment. |
