ASME SA 266 GR.2N Head For High-Pressure Heat Exchangers ,Reactors ,Storage Tanks
SA-266 Gr.2N head is widely used in pressure vessels and boiler systems for non-corrosive media due to its economy, medium temperature stability and easy processing. In sulfur-containing or acidic environments, it is recommended to upgrade to Cr-Mo alloy steel (such as SA-387 Gr.11) or stainless steel (SA-240 304L), and strictly follow the manufacturing and testing standards to ensure safe service.
The butterfly head consists of the crown part (Crown Radius) and the folding edge transition zone (Knuckle Radius), and its geometry is between the elliptical head and the flat cover.
The elliptical head consists of the semi-major axis (a) and the semi-minor axis (b). Its standard shape is 2:1 elliptical ratio (i.e. a/b=2), and it is one of the most widely used head types in pressure vessels.
Butterfly head Low manufacturing cost, simple molding Large stress concentration, weaker pressure bearing capacity than elliptical head Medium and low pressure, infrequent cyclic loads
Elliptical head Uniform stress distribution, high pressure bearing High mold cost, complex deep drawing process High pressure, fatigue load environment
Chemical Composition Requirements
| Item |
Chemical Req. for ASTM A266, % |
| Gr. 1 & 2 |
Gr. 3 |
Gr. 4 |
| C |
≤ 0.30 |
≤ 0.35 |
≤ 0.30 |
| Mn |
0.40~1.05 |
0.80~1.35 |
0.80~1.35 |
| P |
≤ 0.025 |
≤ 0.025 |
≤ 0.025 |
| S |
≤ 0.025 |
≤ 0.025 |
≤ 0.025 |
| Si |
0.15~0.35 |
0.15~0.35 |
0.15~0.35 |
Heat Treatment
After forging and before reheating for heat treatment, the forgings in accordance with ASTM A266 shall be cooled in such a manner as to prevent injury and to accomplish transformation. All the ASTM A266 forgings shall be heat treated by one of the four processes: annealing, normalizing, normalizing and tempering, or liquid quenching and tempering. When tempering is performed, it shall be at a subcritical temperature, but no less than 1100°F [595°C].
Mechanical Properties
Tensile
Requirements |
Gr. 1 |
Gr. 2 & 4 |
Gr. 3 |
T.S min.
ksi [Mpa] |
60~85
[415~585] |
70~95
[485~655] |
75~100
[515~690] |
Y.S min.
ksi [Mpa] |
30
[205] |
36
[250] |
37.5
[260] |
EL. in 2" or
[62.5 mm]
min. % |
23
[21] |
20
[18] |
19
[17] |
R.o.A
min. % |
38 |
33 |
30 |
ASTM A266
Grade |
Brinell Hardness
HBW |
| 1 |
121~170 |
| 2 |
137~197 |
| 3 |
156~207 |
| 4 |
137~197 |
Application scenarios of heads
Typical equipment:
Pressure vessels: end heads of reactors, storage tanks, and heat exchangers (such as elliptical and butterfly heads).
Boiler system: steam drums and header heads, design temperature ≤425°C.
Petrochemical units: hemispherical heads of hydrogenation reactors and fractionation towers, resistant to medium-temperature hydrogen corrosion.
Applicable media:
Non-corrosive fluids (water, steam, oil products).
Weakly corrosive environment (containing a small amount of H₂S/CO₂, sulfur content needs to be controlled).
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