ASME SA336 F5N Heat Exchanger Tubesheet
What is SA336 F5N Heat Exchanger Tubesheet?
A heat exchanger tubesheet is a critical component in
shell-and-tube heat exchangers, acting as a support structure that
holds the tubes in place and ensures proper fluid separation
between the shell side and tube side.
Specification:
Governed by ASME/ASTM SA-336, a standard for forged steel fittings
and components designed for high-temperature and high-pressure
service.
Grade F5N is a 5% chromium, 0.5% molybdenum (Cr-Mo) alloy steel
with normalized heat treatment (the "N" suffix).
Key Composition & Properties:
Chemical Composition:
Cr: 4.0–6.0%, Mo: 0.45–0.65%, C: ≤0.15% (enhanced weldability vs.
standard F5).
Mechanical Properties:
Tensile Strength: ≥485 MPa (70 ksi)
Yield Strength: ≥275 MPa (40 ksi)
High creep resistance at temperatures up to 600°C (1112°F).
Improved toughness due to normalized heat treatment.
Why SA-336 F5N for Tubesheets?
High-Temperature Performance:
Retains strength and resists deformation under prolonged thermal
stress (ideal for heat exchangers in refineries, power plants, and
chemical processing).
Corrosion & Oxidation Resistance:
Chromium content provides resistance to oxidation and sulfidation
(common in sour gas or crude oil environments).
Suitable for hydrogen service (resists hydrogen embrittlement).
Weldability & Fabrication:
Lower carbon content compared to standard F5 reduces pre/post-weld
heat treatment requirements.
Compatible with cladding (e.g., stainless steel overlay) for
aggressive media.
Application in Heat Exchangers
Role of the Tubesheet:
Acts as a structural anchor for tubes, maintaining alignment and
sealing shell/tube-side fluids.
Must withstand differential thermal expansion, pressure loads, and
cyclic stresses.
Typical Use Cases:
Refinery Heat Exchangers: Handling hydrocarbons, H₂S, or
high-pressure steam.
Power Plants: Feedwater heaters, condensers, or boilers.
Hydrogen or Ammonia Plants: High-pressure, high-temperature
service.
Design & Manufacturing Compliance
ASME Standards:
ASME BPVC Section VIII: Governs design, material selection, and
fabrication of pressure vessels/tubesheets.
Section II (Materials): Specifies SA-336 F5N chemical/mechanical
requirements.
Section IX: Welding procedures (e.g., SMAW, GTAW) for Cr-Mo steels.
Fabrication Steps:
Forging: SA-336 F5N is forged to shape for superior grain
structure.
Drilling: Precision drilling of tube holes (TEMA standards for
pitch/tolerance).
Heat Treatment: Normalized (heated to 900°C+ and air-cooled) to
refine microstructure.
Testing & Inspection:
NDT: Ultrasonic testing (UT) or radiography (RT) for defects.
Hydrostatic Testing: Validates pressure integrity.
Hardness Testing: Ensures compliance post-welding.
Comparison with Similar Materials
| Material | Application | Advantages over SA-336 F5N | Limitations |
| SA-387 Gr.5 Cl.2 | Plate material for shells/heads | Similar Cr-Mo content, cheaper for flat components | Less toughness than forged F5N |
| SA-182 F5N | Forged flanges/fittings | Same normalized grade, compatible with tubesheets | Not used for large-diameter tubesheets |
| Carbon Steel (SA-516) | Low-temp exchangers | Lower cost | Poor high-temp strength & corrosion resistance |
Key Considerations for SA-336 F5N Tubesheets
Welding Challenges: Requires low-hydrogen electrodes (e.g.,
E8018-B2) and strict PWHT (post-weld heat treatment).
Thermal Stress Management: Differential expansion between tubes
(e.g., stainless steel) and the F5N tubesheet must be addressed.
Corrosion Protection: Cladding or overlay may be needed for highly
corrosive fluids (e.g., chlorides).
Conclusion
The ASME SA-336 F5N tubesheet is a robust choice for demanding heat
exchanger applications, offering a balance of high-temperature
strength, corrosion resistance, and weldability. Its normalized
structure ensures reliability in critical industries like refining,
petrochemicals, and power generation.
