A VLCC (Very Large Crude Carrier) is a very large crude oil tanker of 300,000 DWT and above; its main engine reaches up to 25 MW, requiring enormous cooling capacity. The vessel adopts a "central cooling" concept: seawater passes only through the central cooler to cool a circulating fresh-water loop (central fresh water), which in turn cools each auxiliary unit. SAMIT titanium plate heat exchangers are the core of the central cooler.
1. Project Background
Customer
A large domestic shipping company; newly built 320,000 DWT VLCC tanker, Chinese flag.
Vessel Particulars
LOA 333 m, beam 60 m, deadweight 320,000 DWT, main engine 25 MW (low-speed two-stroke).
Cooling Demand
- Central cooler total heat load 25 MW
- Seawater temperature -2 ~ 32 ℃ (global voyages)
- Fresh water outlet ≤ 36 ℃
2. Technical Solution
The SAMIT T10 titanium plate heat exchanger was adopted, with 90 m² per unit. Three units run in parallel (no standby); each carries 33% of the total load, so a single-unit failure still retains 66% cooling capacity. Seawater-side plates are commercially pure Titanium Grade 1, fresh-water-side plates are 316L, and plate thickness is 0.6 mm.
| Parameter | Seawater Side (Cold) | Central Fresh-Water Side (Hot) |
|---|---|---|
| Medium | Seawater (salinity 3.5%) | Fresh water + corrosion inhibitor |
| Inlet/outlet temp. | 30 / 40 ℃ (summer) | 45 / 36 ℃ |
| Flow rate | 1500 m³/h | 1100 m³/h |
| Pressure rating | PN10 | PN10 |
| Pressure drop | 55 kPa | 42 kPa |
| Heat load | 9 MW (per unit) | |
| Plate material | Titanium Grade 1 (seawater side) | 316L (fresh water side) |
3. Process Flow
4. Implementation
- Design: Calculated the 25 MW total cooling load per DNV rules; configured 3 titanium PHEs in parallel so a single-unit failure does not force a main-engine power reduction.
- Material selection: Seawater side uses commercially pure Titanium Grade 1 (best seawater corrosion resistance), fresh-water side uses 316L; gaskets are classification-society-certified EPDM.
- Class certification: Passed DNV, CCS, and LR classification, with a 25-year design-life report.
Why titanium is necessary: 316L stainless steel is prone to pitting and crevice corrosion in seawater at ≥ 25 ℃, and the attachment of marine organisms (barnacles, algae) accelerates corrosion. Commercially pure Titanium Grade 1 has a seawater corrosion rate < 0.001 mm/year — about 1/1000 that of 316L — guaranteeing zero plate replacement over the 25-year design life. This is the core rationale for SAMIT marine PHEs.
5. Operating Results
Heat Transfer Performance
Full-load K value 5800 W/(m²·K); main-engine cooling-water outlet stable at 36 ± 0.8 ℃.
Corrosion Resistance
180,000 nautical miles over 3 years; zero pitting on titanium plates, zero gasket leakage.
Anti-Fouling
High-turbulence plate channels + quarterly CIP back-flush; zero marine-organism attachment.
6. Lessons Learned
The core of marine central-cooler selection is "seawater corrosion resistance." Any scheme using 316L instead of titanium will suffer pitting leaks within 3–5 years. Although SAMIT T10 titanium PHEs cost ~60% more upfront than 316L, their 25-year life-cycle cost (including off-hire losses) is only 1/3 that of a 316L scheme. We recommend uniformly selecting titanium plates for any seawater-service PHE.