Seismic Reinforcement and Maintenance

Structural reinforcement of floating roof tanks is ongoing, in accordance with revisions to the Fire Service Act, to prevent damage or sinking of floating roofs. Ishii Iron Works has conducted structural evaluations of floating roofs, proposed optimal retrofitting methods, and carried out numerous seismic reinforcement projects for floating roofs. We will continue to carry out regular maintenance work as well as floating roof replacements and retrofitting work in accordance with regulatory requirements and mandated reinforcement criteria.

On September 26, 2003, a fire broke out at an external floating roof storage tank during the Tokachi-Oki Earthquake. The fire was believed to have been caused by damage and sinking of the floating roof due to sloshing of the liquid surface, triggered by long-period seismic motion. In response to this incident, the Fire Service Act was revised, prompting a re-evaluation of the seismic performance of floating roofs and the implementation of retrofitting measures that consider buoyancy and structural integrity.

Spherical tanks and gas holders are constructed in accordance with applicable regulations depending on the type of stored contents and the nature of the business (e.g., the High Pressure Gas Safety Act, Gas Business Act, etc.). At our company, we carry out seismic performance evaluations in compliance with these regulations, and propose and implement methods of seismic reinforcement.

Spherical tanks sway in various directions when an earthquake occurs, placing significant stress on the supporting structures (columns, braces, etc.) that hold the spheres, which contain flammable gas. If the structural strength is insufficient, cracks or fractures may result. A major accident occurred during the Great East Japan Earthquake, for instance, due to the fracturing of a brace—one of the tank’s key supporting structures. In light of such incidents, the seismic performance of spherical tanks has been re-evaluated, and reinforcement measures have been implemented for components found to be structurally inadequate.