Amended scrappage plan due to contaminated compartments in double-deck floating roof

In September 2019, we were working on dismantling a double-deck floating roof. Every so often, major maintenance is carried out on large storage tanks, and in some cases, the 500-tonne heavy roofs can no longer be repaired. It is up to us to systematically dismantle these roofs. You can read how we usually go about this in another article on replacing a double-deck floating roof.

This time, we had to deal with contaminated sections in the roof. The contamination was caused by leakage. The flammable product in the storage tanks had migrated into these compartments. This called for a slightly different approach than usual, which we detailed in an amended engineering plan.

Removal of contaminated compartments

In the upper deck, we made inspection hatches with air tools to determine where most contamination was located. Based on this information, we made changes to the remaining dismantling method. We first cleaned the most contaminated areas and adjusted the cutting lines according to the contamination. Where there is dirt, it is not possible to cut with a burner because of the risk of fire.

Additional support under the lower deck

Normally, we place the lower deck on outriggers before dismantling, so that it cannot sag while work is being carried out on it. In this case, the roof was already standing on its own steel legs. However, these legs were not enough to stabilise the roof, as other forces are released during dismantling. We therefore added additional support and partly relocated the work to ensure that we could work on dismantling it in a safe way.

Extra early shifts

We were not alone in the tank pit. Another contractor, who was responsible for blasting the tank (i.e. removing the existing paint), was carrying out work on the same days. Since a lot of dust and blasting grit is released during blasting, it was important that our guys were gone before the blasting began at 14:00. In order to ensure that the double-deck floating roof was dismantled before the deadline, we started our dismantling activities at 05:00 in the morning. This enabled us to complete our work within five weeks, and, once again, this project was completed efficiently.