Roof Tilting Product Overflow Ms Floating Roof Tank
Click here to load reader
-
Upload
sonn-the-great -
Category
Documents
-
view
44 -
download
1
description
Transcript of Roof Tilting Product Overflow Ms Floating Roof Tank
RoofTiltingandproductoverflowinMSFloatingRoofTank
12 metre dia x 11 mts height (1000 KL) external floating roof tank (double deck) was in operation in a POL terminal. In the aftermath of heavy rain fall, the roof was found to have tilted. Due to the tilt, MS was exposed on one part of the roof.
The location suspended all operations of the tank, applied AFFF foam for blanketing the exposed product and subsequently, tried to evacuate the tank fully by transferring the product to suitable adjacent tank by drawing of product from the water draw off nozzle.
Evacuation of product failed to improve the tilt and non‐submerged pontoons were filled with water to counter the tilt while simultaneously withdrawing the product from the tank. After filling two pontoons with water, the tilted deck got unstuck and came back to its normal position. Thereafter, the tank was emptied out.
The OMC investigation in the incident revealed that:
1. The filling height of the tank was restricted to 700 cm in view of sweating observed in the shell above this level.
2. The gross dip level at the time of incident was 335 cms and the tank was resting on the short legs after the tilt.
3. The entire deck moved towards the submerged section and further movement was obstructed by the dip‐well acting as a hinge. The movement of the roof bent the dip pipe and about 600 mm gap was created between the shell and the roof. The rolling ladder was also twisted.
4. Four of the 13 pontoons near the dip‐well pipe were partially filled with product and water mix and the rest of the pontoons were fully submerged.
5. Some degree of deformation of the shell was also observed in the form of dripping from the tank body outlet nozzle between the shell and the body valve.
The probable causes found out during the investigation are:
1. The tank roof got flooded with rain water consequence to the heavy rain fall in the three days preceding the incident.
2. The accommodated rain water on the roof got its way to the pontoons through the heavily corroded top deck having large corrosion holes.
3. The accumulation in the pontoons caused tilt and subsequent rotation against the dip well pipe displacing the weather shields and distorting the secondary shield, thus creating the gap between the roof and the shell through which the product flooded the roof.
The learning from this incident is as follows:
1. When sweating was observed on the top strakes of the shell, necessary investigation should have been conducted on the material integrity of the roof as the roof is more exposed to the elements than the shell.
2. In‐spite of the tank roof having developed corrosion holes, the tank was neither decommissioned nor was further maintenance work taken up.
3. Routine roof inspection of this tank was not effective otherwise the level of corrosion could not have reached this level.
4. Routine monsoon precautions and SOPs for floating roof tanks after heavy rainfalls were not followed.