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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.