For a shell and tube marine oil cooler, material selection is critical due to seawater corrosion, fouling, and high mechanical stresses. Below are the recommended materials for different components:
1. Shell (Oil Side)
- Primary Material:
- Carbon Steel (CS) with corrosion-resistant coating (e.g., epoxy or rubber lining) – Cost-effective but requires maintenance.
- Stainless Steel (SS 316/316L) – Better corrosion resistance, preferred for harsh marine environments.
- Duplex Stainless Steel (SAF 2205) – Higher strength and chloride resistance than SS 316.
- Why?
- The oil side is less corrosive than the water side, but the shell must still resist internal oil degradation and external marine atmosphere.
2. Tubes (Cooling Medium Side – Usually Seawater)
- Best Options:
- Titanium (Grade 2 or Gr. 5) – Best for seawater, immune to chloride corrosion, biofouling-resistant, and long-lasting (used in naval & high-end marine applications).
- Copper-Nickel Alloys (Cu-Ni 90/10 or 70/30) – Good seawater resistance, anti-fouling properties, and cost-effective compared to titanium.
- Aluminum Brass (76% Cu, 22% Zn, 2% Al) – Cheaper than Cu-Ni but less durable in polluted seawater.
- Avoid:
- Stainless Steel (SS 304/316) – Prone to pitting & crevice corrosion in stagnant or chlorinated seawater.
- Admiralty Brass – Not suitable for polluted or high-velocity seawater.
- 3. Tube Sheets (Holds Tubes in Place)
- Material:
- Naval Brass (for Cu-Ni tubes) or Titanium-clad Carbon Steel (for Ti tubes).
- Stainless Steel (SS 316L) with Cathodic Protection – If used, must have zinc anodes.
- Why?
- Tube sheets face galvanic corrosion due to dissimilar metals (e.g., Cu-Ni tubes + CS shell).
- 4. End Caps / Headers (Water Side)
- Cast Iron (with coating) – Economical but prone to rust.
- Bronze (for Cu-Ni systems) – Corrosion-resistant.
- Stainless Steel (SS 316) – Best for longevity.
- 5. Baffles & Supports
- SS 316 or Coated Carbon Steel – Must resist water turbulence and erosion.
- Key Considerations for Marine Oil Coolers:
- Seawater Velocity: High flow reduces fouling but increases erosion → Titanium is best for high-velocity seawater.
- Sacrificial Anodes (Zinc) – Needed if dissimilar metals are used (e.g., CS shell + Cu-Ni tubes).
- Double-Wall Design – Prevents oil-seawater mixing in case of leakage (IMO/SOLAS compliance for some vessels).
- Best Material Combination for Marine Oil Cooler:
- Final Recommendation:
- For maximum durability & low maintenance → Titanium tubes + SS 316L shell.
- For cost-effective solution → Cu-Ni 90/10 tubes + coated CS shell + zinc