By Capt. Neeraj Bharti, Founder, Master Mariner · Published · 2 min read
End-of-life tank coating: why it holds black oil and how to plan around it
Every tank coating has a working life. When it is new, a well-applied epoxy coating sheds residue easily and cleans to a high standard. As it ages, breaks down and becomes porous, it starts to hold what it carries. For a ship moving from fuel oil to a clean product, that changes the whole changeover.
Ship due at an Indian port? We run cargo hold cleaning in India at 32 ports, from our Kandla and Mumbai offices.
What happens to an ageing coating
Over years of service, cargo heating, washing, mechanical damage and chemical exposure wear a coating down. Typical signs:
- Softening or porosity, where the coating absorbs cargo into its surface
- Blistering and pinholes
- Breakdown and rust spots, especially on tank bottoms, around coils and at welds
- Staining that does not wash off
A coating in that state behaves like a sponge for dark cargo. It can look clean straight after washing and then bleed colour or residue into the next cargo. Rust spots and flaking coating shed particulates.
Why it matters for a changeover
- Inspection. Inspectors can reject tanks that are stained even after correct washing.
- Colour and contamination. Black oil absorbed into the coating can affect colour-sensitive grades such as jet fuel, gasoline or naphtha.
- More washing does not fix it. Extra hot washing on a failing coating removes surface residue but cannot get out what the coating has absorbed, and aggressive chemicals may damage it further.
Assess before you fix
Before fixing a sensitive clean cargo after dirty trades, find out what the coating can actually do:
- Review the coating history: type, age and when it was last renewed or repaired.
- Inspect the tanks: bottoms, around coils, welds and areas of known damage. Photographs help the commercial team decide.
- Check the coating manufacturer's cargo resistance list for the next grade and for any chemicals you plan to use.
- Consider a lower-risk first clean cargo, such as gasoil, before a jet or naphtha nomination, if the coating is doubtful.
Cleaning old coating carefully
- Use heat sensibly. Within the coating's limits, hot washing is still the best way to remove dark cargo.
- Choose chemicals the coating can tolerate, and rinse thoroughly.
- Pay extra attention to areas of breakdown, where residue collects.
- Dry thoroughly. Water in damaged areas leads to rust and particulates.
The longer-term decision
If a ship is meant to trade clean after a dirty history, coating condition is part of the commercial plan, not just the cleaning plan. A coating renewal at the next docking may be what makes the clean trade possible. The DPP to CPP changeover guide covers the wider planning, and failed tank inspection after a changeover covers recovery when coating causes a rejection.
How Cleanship helps
During a changeover our teams record coating condition tank by tank, with photographs, so the operator knows where the risks are before nominating a sensitive grade. See our DPP and CPP tank cleaning service or contact us with your vessel and cargo history.
Sources & further reading
Frequently asked questions
Why does old tank coating hold black oil?
As coatings age and break down they become porous and absorb cargo into their surface, so dark cargo can stay in the coating even after correct washing.
Can extra washing fix a stained coating?
Not fully. More washing removes surface residue but cannot remove what the coating has absorbed, and aggressive chemicals may damage it further.
Should coating condition be checked before fixing jet fuel?
Yes. Jet and other colour-sensitive grades are at most risk from a coating that holds dark cargo, so coating should be assessed before the nomination.
What is a coating resistance list?
It is the coating manufacturer's list of cargoes and chemicals the coating can safely carry or be exposed to, and under what conditions. It should be checked for both the next cargo and any cleaning chemicals.
- tank coating condition changeover
- epoxy tank coating black oil
- coating breakdown cargo tank
- tank coating absorption
- changeover old coating
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