– The tank is built of sheet steel, is 21 meters high and 21 meters in diameter, but it’s when you step into it that you realize how big it really is, Dan explains.
In order to be able to get material inside, as well as be able to work inside the cistern, the first effort was to cut up an entrance in the cistern wall. Step two was to tear out everything that was inside, such as heating coils. The cistern had been decontaminated before our work began, but some coked bitumen remained on the walls, which could come loose during the work. To protect the staff, an interior roof was constructed.
– The roof was a successful solution. The alternative would have been to use a scaffolding in the tank and hack down everything. Only that work would probably have taken 2 weeks, explains Michael Norberg, Acting Depot Manager at Nynas.
The biggest challenge was the incline the floor needed, in order to achieve a more efficient emptying, at the same time as the plates must lie flat in a round-shaped cistern.
Dan explains the challenge of cutting a cylinder at an angle and the solution of comparing the technique of paving:
– If you divide a cylinder by 10 degrees, the cut surface will not be round, but oval. Regarding the technique for getting an evenly inclined surface, we scaled up the principle for when placing stone slabs on a driveway
The proper inclination was facilitated by drawing a line on the wall with a laser and by mounting rulers in the fall line from high to low throughout the cistern. The new sheet metal floor was built above the old one and rested on the ruler system. The space between the old and the new floor was filled with 90 cubic meters of sand, which was leveled by scraping the ruler system with boards.
In order to assemble the patchwork of sheets with inclination, calculations were made which were clarified in a sheet metal scheme. A total of 90 plates of 3 x 15 m were lifted into the cistern and welded together.
To avoid the difficulty of rounding the plates on the inside, the plates was pushed out at the bottom of the wall by slitting openings. This had to be done in sections of 3 meters, so the cistern wouldn’t risk settling. Each section was stapled and welded together, before the next was opened. In the end, the parts that protruded on the outside of the cistern were cut.
For each type of weld and thickness, welding instructions (WPS) were written, which refer to Jernbro’s welding procedures. It was everything from single to multi-layer vessel joints, butt joints and v-joints. In total, about 600 m were welded (and that without a single remark from the inspection company).
– The welding looks extremely good and it feels great that the customer has a strong trust in us. The inspection company, is also satisfied with our work and has not had any comments. All collaborations have been super. Internally, we also have extremely dedicated staff, which makes the work extra fun, says Dan
– The project is now finished and the first ship has filled the tank. The project has moved forward through out the project and the agreed time schedule was kept. This is especially important when spring and summer is on its way, since it’s then roads are built (for which the content of the cistern is to be used). We are completely satisfied. Everything regarding documentation is also in order, and we have already received all drawings and certificates, concludes Michael Norberg at Nynas.
