ASME SA266 Gr.2N Heat Exchanger Tubesheet as per ASME Sec VIII
What is ASME SA266 Gr.2N Specification?
The ASME SA-266 Gr.2N specification covers carbon steel forgings
used in pressure vessels and heat exchangers, particularly for
tubesheets. This material is widely used in shell-and-tube heat
exchangers, condensers, and boilers due to its good mechanical
properties, weldability, and cost-effectiveness.
The "2N" designation indicates that the material is supplied in the
normalized heat-treated condition, which enhances its strength and
toughness compared to non-normalized grades.
Chemical Composition (ASME SA-266 Gr.2N)
Element | Composition (%) |
|---|
Carbon (C) | ≤ 0.25 |
Manganese (Mn) | 0.60 – 1.35 |
Phosphorus (P) | ≤ 0.025 |
Sulfur (S) | ≤ 0.025 |
Silicon (Si) | 0.15 – 0.35 |
Nickel (Ni) | ≤ 0.40 (optional for low-temp toughness) |
Mechanical Properties
Property | Value |
|---|
Tensile Strength | 485 – 620 MPa (70 – 90 ksi) |
Yield Strength (min) | 260 MPa (38 ksi) |
Elongation (min) | 21% |
Hardness (Brinell, max) | 187 HB |
Heat Treatment
Normalized (N) to refine grain structure and improve mechanical
properties.
Optional Post-Weld Heat Treatment (PWHT) if welding is performed.
Why Use SA-266 Gr.2N for Heat Exchanger Tubesheets?
Advantages
Cost-Effective – More economical than stainless steel or nickel
alloy tubesheets.
Good Weldability – Compatible with common welding techniques (SMAW,
GTAW, SAW).
ASME Code Compliance – Meets ASME Boiler and Pressure Vessel Code
(BPVC), Section VIII for pressure vessels.
Moderate Corrosion Resistance – Suitable for non-severe
environments when properly maintained.
Limitations
Not for Highly Corrosive Service – Requires cladding or coatings if
exposed to acidic/aggressive media.
Limited High-Temperature Use – Max recommended temperature: ~400°C
(750°F).
Galvanic Corrosion Risk – If paired with stainless steel or nickel
alloy tubes (e.g., UNS N08810), isolation or cathodic protection
may be needed.
Tubesheet Design & Fabrication Considerations
Design Codes & Standards
ASME BPVC Section VIII, Div. 1 or 2 (UG-34 for flat
heads/tubesheets).
TEMA (Tubular Exchanger Manufacturers Association) for hole
patterns & tolerances.
Tube-to-Tubesheet Attachment Methods
Method | Description |
|---|
Mechanical Expansion | Tubes are rolled into holes for a tight fit. |
Seal Welding | Prevents leakage between tube and tubesheet. |
Strength Welding | Provides structural integrity under high pressure. |
Explosive Bonding | Used for clad tubesheets (carbon steel + corrosion-resistant
layer). |
Machining & Quality Control
Precision Drilling – Hole diameter, pitch, and alignment must meet
TEMA standards.
Non-Destructive Testing (NDT) – Ultrasonic Testing (UT), Dye
Penetrant (PT), or Radiography (RT) for weld inspection.
Surface Finish – Smooth machining reduces crevice corrosion risk.
Common Applications of SA-266 Gr.2N Tubesheets
Oil & Gas – Heat exchangers in refineries.
Power Plants – Condensers and feedwater heaters.
Chemical Processing – Moderate-temperature exchangers.
HVAC Systems – Industrial cooling applications.
Alternative Materials for Tubesheets
If SA-266 Gr.2N is unsuitable, consider:
SA-266 Gr.3 (Higher strength carbon steel).
SA-516 Gr.70 (Pressure vessel steel).
Stainless Steel (SA-240 Type 304/316) – Better corrosion
resistance.
Clad Tubesheets (SA-263/SA-264) – Carbon steel with
stainless/nickel overlay.
The ASME SA-266 Gr.2N tubesheet is a reliable and economical choice
for moderate-pressure and temperature heat exchangers. Proper
material selection, design, and fabrication ensure long-term
performance.
