For the MV Bergensfjord, we received three NRF box coolers with heavy marine fouling. Large sections of the tube bundles were covered with mussels, shells, sludge and other organic growth. This may not only have restricted heat transfer, but also made it difficult to assess the actual technical condition of the cooling tubes.
We therefore carried out a complete service process, from intake inspection and cleaning to repairs, pressure testing and recoating the units. All three box coolers ultimately passed a pressure test at 5 bar for 30 minutes.
Condition on arrival
We received 3 NRF box coolers for MV Bergensfjord in 2 different sizes:
- Box cooler 1: 1205 x 460 x 1210 mm, serial number 10-0340-5A
- Box cooler 2: 1925 x 460 x 1805 mm, serial number 10-0240-8C
- Box cooler 3: 1925 x 460 x 1805 mm, serial number 10-0340-8B
The box coolers were delivered to our workshop in wooden transport crates. During the intake inspection, it became clear that not all crates were in good condition. This was documented before the units underwent any further work.
The box coolers themselves were heavily fouled. Mussels, shells, sludge and organic material had accumulated in and around the closely spaced cooling tubes. In some areas, the marine growth was so dense that large sections of the tube bundle were barely visible.
A box cooler transfers heat from the vessel’s closed cooling circuit to the surrounding seawater through its cooling tubes. A thick layer of marine growth can act as an insulating layer. The fouling therefore had to be removed before the underlying technical condition could be properly assessed.
A magnetic test was also performed during the intake inspection. The plates and tubes proved to be non-magnetic. During the initial inspection, the replacement of two tubes was recommended for cooler 2 and cooler 3. All three units required internal and external cleaning, followed by pressure testing.
The technical challenge
The fouling presented a twofold challenge in this project. On the one hand, biofouling can restrict contact between the cooling tubes and the surrounding seawater. On the other, a thick layer of marine growth can conceal corrosion, damage and weakened areas.
The box coolers could therefore not be recoated straight away. A new coating must not conceal underlying technical issues. We first needed to establish whether the cooling tubes and connections were mechanically sound and leak-tight.
We therefore adopted a phased approach:
- Register and visually inspect the units
- Clean the units internally and externally
- Reinspect the tube bundles
- Replace or repair damaged cooling tubes
- Pressure-test each unit separately
- Recoat the box coolers
- Perform a final pressure test
Cleaning and inspection of the tube bundles
The three box coolers were thoroughly cleaned. The final documentation confirms that the units were chemically cleaned. Removing the mussels, shells, deposits and other fouling made the individual cooling tubes and tube sheets accessible and visible again.
Cleaning a box cooler is not merely a cosmetic procedure. It is a necessary step in order to:
- Visually inspect the tubes
- Reveal damage and weakened areas
- Assess the condition of the tube sheet
- Carry out targeted repairs
- Enable a representative pressure test
Only after cleaning could the true extent of the required repairs be determined.
Repairing the cooling tubes
Following cleaning and inspection, cooling tubes were replaced in all three units:
- One cooling tube was replaced in cooler 1
- Two cooling tubes were replaced in cooler 2
- Two cooling tubes were replaced in cooler 3
A damaged cooling tube can affect the pressure integrity of the closed cooling circuit and may eventually cause leakage. The affected tubes were therefore addressed before the units underwent any further finishing work.
One cooling tube in cooler 3 was plugged. This takes the tube out of service and seals it, preventing any medium from flowing through it.
Pressure testing after cleaning and repair
Following the initial repairs, each box cooler was pressure-tested separately. The test pressure was 5 bar and was held for 30 minutes.
The start and end of each test were documented with photographs of the pressure gauge and the time record. All three box coolers passed this pressure test.
A pressure test checks whether the unit maintains the specified test pressure throughout the test period and whether any visible leakage occurs. Approval means that the units successfully passed the test performed. However, a pressure test does not automatically rule out every possible form of future material degradation.
Coating and protection of the units
Following cleaning, repair and pressure testing, all three box coolers received a new protective coating. Before this finish could be applied, it first had to be established that the units were technically sound and leak-tight.
The new coating helps protect surfaces and structural components against corrosion and other effects of the marine environment. Coating is not a standalone treatment; together with inspection, cleaning, repair and pressure testing, it forms an important part of the complete maintenance process.
Final inspection and second pressure test
After the coating work, the three box coolers were pressure-tested again. During this final inspection, the test pressure was once more 5 bar and was held for 30 minutes.
All three final pressure tests were approved.
This second inspection is important. Between the first pressure test and delivery, the units are moved, handled and coated. Testing them again confirms whether the box coolers have remained leak-tight after all the work performed.
New transport crates were also supplied. New gaskets were available and had been supplied by the owner. The documentation does not confirm that these gaskets were installed during this project. After completion, the units were prepared for delivery and further handling.
The result
Following completion of the project:
- Three NRF box coolers had been chemically cleaned
- The heavy marine growth had been removed
- The tube bundles were visible and accessible for inspection again
- A total of five cooling tube replacements had been recorded
- One additional cooling tube had been plugged in cooler 3
- All units had successfully passed a pressure test after the repairs
- All three box coolers had been recoated
- All units had successfully passed another pressure test during the final inspection
- New transport crates had been supplied
- The box coolers had been prepared for delivery
This provided the client with a documented overview of the condition, repairs and test results for each unit. The units were not simply cleaned; they were technically inspected before being refinished.
More than removing marine growth
This project shows why box cooler maintenance involves more than removing mussels and other marine growth. Cleaning makes inspection possible. Inspection reveals hidden damage. The required repairs can then be carried out and verified.
The sequence is essential: first clean and inspect, then repair and test, followed by recoating and a final test. This prevents fouling or a new coating from obscuring the actual technical condition of a unit.
Does your box cooler require maintenance?
Is your box cooler fouled, corroded or due for pressure testing? Have the unit inspected before reduced heat transfer or leakage leads to unexpected problems.
Blue Orange provides the complete service, from cleaning and technical inspection to repairs, coating and final inspection.