ASME SA266 Gr.2N Heat Exchanger Tubesheet as per ASME Sec VIII

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)

Mechanical Properties

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

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.