Blasting and coating oil tanks during winter months

Our customer had been contracted to prep the surfaces and to apply a coating liner system on the interior sections of two newly constructed giant crude oil storage tankers. Each tank was 225 feet in diameter and 62 feet high with a floating roof. The assignment was to abrasive blast the inside surfaces of the steel tanks, clean out the abrasive, prepare a clean, dry surface for coating and spray the coatings on the floors and walls to a height of two feet above the floors with an epoxy coating. The two-foot height for coating the walls was specified to protect the surface against water that accumulates in the tank and can rise to that level below the oil stored in the tanks.

Challenge

Because the customer needed to meet a deadline to store incoming crude oil, the challenge was to complete both tanks within 28 days, versus a normal 60-day schedule. This demanding schedule had to be met during a cool, rainy period, which was likely to create condensation on the work surface of the tank.

“The major threat to the integrity of the coating was the possibility of the formation of ‘rust bloom’ corrosion that can occur on steel surfaces between the blasting phase and application of the paint, during damp conditions.”

“The atmosphere is normally very humid, but conditions in April were made worse by heavy rains. This meant we could expect condensation on the inside of the tank.”

Solution

Because of the humid air and cool outside temperatures, condensation could easily form on the inside tank surfaces during the work period.

“We knew we could never meet the job specifications under those conditions. We needed to first create a dry atmosphere and lower the dew point inside the tanks. We also needed to keep the temperature high enough to speed the cure rate of the coating.”

For a solution, our client turned to Polygon, his provider of dehumidification services for the past 15 years. Polygon was asked to build a rental system that would hold the blast by eliminating any possibility of condensation forming on the tank walls.

After analysing the project parameters, Polygon experts suggested the use of propane gas-fired desiccant dehumidifier units, which are effective in the removal of high levels of moisture at high rates of airflow. An added advantage of using the desiccant units in this situation was the ability to utilise the heat that is a natural by-product of the dehumidification process to boost the cure rate of the coating. With Polygon’s system in place, work could continue around the clock for 13 days on each tank. As a result, the desiccant dehumidifiers assured that the company met the deadline and saved money in the process.

The Benefits

Polygon’s solution delivered significant cost savings and operational efficiencies. The controlled humidity environment enabled continuous blasting, cleaning, and coating without delays, ensuring the work could proceed without interruption. Because Polygon’s propane reactivated dehumidifiers required minimal electricity, small generators could be used at the remote site, which helped reduce diesel consumption and overall fuel expenses.

The natural heat produced during the dehumidification process was utilised inside the tank, eliminating the need for a separate bake-out service. This maintained optimal conditions throughout the coating application and significantly reduced curing time.

The client noted:

“Without the Polygon Temporary Humidity Control to control the climate in the tanks, we never would have been able to meet the job completion deadline. Being able to do that helped enhance our relationship with our client and helped build our reputation.”