Anticorrosive protection of internal surfaces of tanks requires high qualifications and attentiveness; besides, it is an unhealthy work. This fact is obvious to those who have ever faced this problem. Any mistake and any infringement of technology related to preparation of the surface, preparation of varnishes, first coats, enamels, infringement of painting and polymerization methods might lead to substantial consequences and imply that the infringer has better start looking for another job immediately, because the first thing the customer sees is rust or corrosion flow over the favorite wall surfaces of the tanks…
All the problems increase with a multiplier effect when it's required to do the coating inside a ready to use vertical tank. A lot of time is required to install scaffolds around the inside wall surface of reservoir and scaffolding alone raises the question of whether the expenses incurred are commensurable to the expected period of tank life!
We ran into such a problem during construction of a terminal for refined oil products, located not far from Drobeta-Turnu-Severin city, Romania. After the tank was erected and installed, as it usually happens, the customer came up with a new request (and available resources of course) to have internal aluminum floating covers installed in a tank of 3000m3 capacity.
The designers strictly required anticorrosive protection of inside wall and roof surfaces (!) of the tank before installing floating cover to ensure its smooth operation. The time for implementation, as usual, was not granted; besides, the tank with a standard design had roof support beams installed inside the tank to reduce atmospheric pressure over the tank.
It was summer and the temperature in Severin, southern Romania was unbearably hot: it reached +46°C (114°F) in shadow and went well above +65°C (149°F) under the sun. Inside the tank, the person who would climb to the upper part of the tank had better pull back immediately to avoid heatstroke. Besides, only ordering scaffolds, assembling them inside the tank and dismantle them after the completion required more time than the time given to us. The painters and specialists were really challenged by the problem.
The painters offered a modified design of rotating struts that was previously applied for other purposes in other projects. The preparation works would take a lot of time that we were already short of. The industrial climber-painters who were performing anticorrosive protection of external surfaces of all tank farm offered a system of rope extensions so complex, that could affect the productivity, and even worse, could compromise the quality of works.
Fantastic technologies also failed to offer a viable solution and we were desperately looking for anyone who could offer a clue. The right solution came from an elderly crane mechanic: If we could extend the maneuverable boom of the crane, in a certain position it would be possible to reach the center of the tank and through the central manhole to lift a board bridge; the person on the bridge could move around and paint once strip around the radius at a time until he finished the whole roof.
Only the available bridge was too heavy; it was even heavier than the capacity of the crane at such length; in addition to that, the size of side manholes was not enough to take the bridge inside the tank without cutting hole on the tank wall. Nevertheless, we liked the idea. The next morning engineers found a beam that, surprisingly, was not sent to new project site; it was extended with a pipe of 325mm diameter, which allowed taking the whole structure into the tank through side manhole without damaging the tank walls.
Safety straps were provided and a form of grill rail was installed as a safeguard. Meantime, the maneuverable boom of the crane was extended, terminators of rise in position of safe rise (not closer than 1.5 meters to the internal part of the tank roof) were installed. The new structure turned out to be very convenient and functional. Within a day all the preparations were done and we were ready to go.
Two specialists could land over two ends of the "beam-bridge" through light hatches on the roof of the tank; they could walk freely and it was reasonably convenient to work without fear. The "beam-bridge" could easily be rotated around either by workers or by support team, who were in the bottom of the tank and holding control slings attached to the "beam-bridge".
Anticorrosive protection of the wall surface from within at the height of 12 meters without damaging structure of the tank roof became a "children game". After seven days, while three industrial climber-painters still were eagerly continuing external surface painting & finishing works, the internal anticorrosive works have been finished.
The three days saved in anticorrosive works came pretty handy; we used them to install the aluminum floating cover inside the tank. Thus the challenge was overcome and on-time completion of work was made possible.