Tanks and vessels
Tank lining is the hardest coating work there is and the most dangerous. The lining sits in permanent immersion where nobody can inspect it, inside a confined space that can turn lethal without warning. Here is what the job actually involves.
Viram Mariv Ltd · Tema, Ghana · 8 min read
External steel gets inspected. Somebody walks past it, notices rust bleeding through, and a maintenance job gets raised. A tank lining gets none of that. It goes into service, the tank fills, and the next time anyone sees it is at the following shutdown — which might be five years away, or ten.
That is why the standards for internal work are higher than anything applied outside, and why a shortcut taken inside a tank does not show up until it has already cost you the tank.
An external coating deals with wetting and drying cycles, UV and atmospheric corrosion. It gets to breathe, and small defects often stay small.
An immersion lining is under permanent liquid contact, frequently at elevated temperature, often against aggressive chemistry, with no oxygen reaching the steel. In that environment a single pinhole does not stay a pinhole. Liquid penetrates it, reaches the substrate, and corrosion spreads sideways underneath the film. The lining is undercut from below and comes away in sheets, sometimes over a large area, from one defect the size of a pin.
A tank lining that has not been holiday-tested has not been finished. There is no visual inspection that finds a pinhole.
Which is why the specification for internal work is almost always ISO 8501-1 Sa 2½ as an absolute minimum, and frequently Sa 3 — white metal, no visible contamination anywhere. Nothing less survives permanent immersion.
Before any of the coating work matters, there is the space itself. A tank is a confined space with one way in, restricted ventilation, and an atmosphere that can go oxygen-deficient or explosive with no warning to the people inside it. Then you generate blast dust and solvent vapour in there.
Confined space fatalities follow a pattern that is grimly consistent worldwide: someone enters, collapses, and the people who go in to help collapse too. More than half of confined space deaths are would-be rescuers.
So the controls are not paperwork. This is what has to be in place before anyone goes through a manway:
None of this moves to suit a programme. If a contractor tells you the standby man can also carry material, or that ventilation can be turned off to reduce noise, that is the whole conversation about how they run their work.
Residue, sludge and scale come out first. Hydrocarbon tanks are cleaned and certified gas-free before any abrasive or hot work begins. This stage is routinely underestimated in both cost and duration, particularly on tanks that have held heavy product for years.
Blasting to the specified grade, with profile measured to ISO 8503 and matched to the lining manufacturer's range — usually deeper than an atmospheric system requires, because immersion linings are thicker and need more to key into.
Soluble salts tested and washed down where levels exceed the specification. Outside a tank, salt contamination shortens a coating's life. Inside a tank in immersion, it destroys the lining. There is no second chance to correct it once the tank is closed.
Which system goes on depends entirely on what the tank holds and how hot it runs:
| System | Typical use |
|---|---|
| Solvent-free epoxy | General product storage, fuel, water. High build, low VOC — important in a ventilated confined space. |
| Novolac epoxy | Aggressive chemistry and higher service temperatures. |
| Glass-flake | Where abrasion or mechanical damage is a factor as well as corrosion. |
| Certified potable systems | Drinking water tanks. Approval for water contact is not optional and not interchangeable. |
Stripe coating comes first — welds, nozzles, manway edges and every internal corner brush-applied before each spray coat. Inside a tank this matters even more than outside, because those are the geometries where spray film thins and where immersion attacks first.
Once the lining is cured, the entire internal surface is spark-tested. A probe is passed across the film at a voltage set against the coating thickness. Where there is a pinhole, void or thin spot, the current jumps and the instrument signals it.
Every defect found is repaired and the area retested. This is slow. On a large tank it takes days. It is also the only method that will find the defects that matter, and skipping it means putting a lining into immersion service with unknown holes in it.
After that, full cure has to be verified before the tank goes back into service. Returning a lining to immersion before it has cured will ruin it, and the pressure to do exactly that — because the outage is running long and the tank is needed — is where a lot of expensive linings have been lost.
Tank work is shutdown work. The tank is out of service, the clock is running, and the cost of the outage usually exceeds the cost of the lining. What makes it go well is deciding the scope before the tank is opened rather than after.
The one thing to build into the budget from the start is steel repair. Once internals are exposed, wasted plate and pitting are found. Not sometimes — nearly always, on any tank that has been in service a while. If there is no provisional allowance for it, you get a variation conversation halfway through an outage that has no slack in it.
Where tanks fall under an inspection regime such as API 653, the intervals and repair requirements your inspector sets govern the scope. Agree hold points with your team or a third-party inspector before the outage opens, not mid-job.
It depends on diameter, internal condition, how much steel repair is found and the cure schedule of the lining. A small vessel can be days. A large storage tank with pitting and repair work is weeks. Any figure given without seeing the tank is a guess.
Yes, using systems certified for drinking water contact. Cure and flushing before return to service are part of the specification and should never be shortened to recover programme.
For internal lining, yes. External shell and roof work can often be done with the tank live, so it is worth splitting the scope — do the external now, hold the internal for the outage.
Work should stop and the condition should be reported with thickness readings. Lining over wasted plate hides a problem rather than fixing it. Steel repair is then priced as a variation once you have seen what is actually there.
That is set by the service, the product and any inspection regime the tank falls under. What matters is that the interval is decided and diarised, because nobody notices a lining failing from the outside until product quality or a leak tells them.
Send us the tank details and the service it holds, and we will come and look. Viram Mariv has delivered internal blasting and lining on silo tanks, treatment plant vessels and storage across the Tema industrial area. Quotations are free.
Written by the Viram Mariv team. We are an industrial surface preparation and protective coating contractor based in Tema, Ghana, working across West Africa.