What is Tank Cleaning?

Storage tanks are used to store and haul liquids and hazardous waste.

Liquids and wastes can either be stored in aboveground (AST) or underground (UST)  tanks.  Tank designs are often dependent on site or job requirement (like after solid separation), meaning that tanks can be of all shapes, sizes, and styles. The size of storage tanks can range from 6,000 to 12 million gallons of liquid.

Because storage tanks are used routinely to store and transport waste, like for the oil and gas industry, they must be cleaned regularly to ensure they remain in good enough condition to continue safely carrying hazardous materials and chemicals.

Why is Tank Cleaning essential?

Storage tanks transport and store materials such as chemicals, corrosives, oil, solid wastes and other potentially dangerous materials. And, like any other vessel that is designed to store and transport hazardous chemicals or waste, it needs to be routinely cleaned.

All tank operations must follow the industry standard set by the The American Petroleum Institute (API) 653 for regular inspections.

Under API 653, regular inspection intervals of ASTs are necessary to evaluate corrosion rates. It is important to ensure the health of the tank itself. Without emptying and cleaning, there can be unknown conditions inside of the tank, which also cause harm to the surrounding environment.

Tank cleaning is crucial to the safety of the environment in which operators work in. For example, tanks should be cleaned to avoid possible reactions between differing substances like explosions, toxic gas release, fires, etc.

When should you clean tanks?

Although inspections are an important time to make sure tanks are clean, it is just one of the reasons why you might need to clean your aboveground or underground storage tanks.

Tank cleanings can be performed for capacity loss, change of product, API inspections, maintenance, repairs and more.

• Change of product - If you plan to store a different product in your tank, a full tank cleaning is most likely necessary. If you are switching from an unrefined product to a refined product, you would need to remove all residue and impurities.
• API Inspections - When it is time for an internal inspection, your tank must be taken out of service, cleaned and prepared for an inspector to enter the storage tank.
• Maintenance - If your tank has service issues or a mechanical failure, you most likely can't repair it while the tank is in service. To make necessary repairs, the tank will need to be emptied, cleaned and be vapor free.

How do you clean tanks?

Before the tank cleaning process can begin, the storage tank must pump out the product that is inside the tank. Although the tank has been drained, there will still be several thousand gallons of product on the floor of the tank, below the low suction line. Once the remaining product below the low suction line has been removed, a tank cleaning company is now able to perform the following steps:

1. All electrical connections on pumps, mixers and similar mechanical equipment must be locked-out (or tagged-out).
2. Drain down lines, remove valves and install appropriately sized blind flanges on tank nozzles and pipe line flanges to isolate the tank from the system.
3. Remove the remaining product from the tank via vacuum truck or other pumping means.
4. Mechanically vent the tank and perform gas freeing to get rid of dangerous vapors, ideally to a lower explosive limit (LEL) of 10 or less.
5. Make confined space entry (comply with OSHA’s regulations and API standards) to clean the tank’s interior.
6. Remove final product puddles via vacuum truck by squeegeeing the tank floor.
7. Power-wash the floor, walls and underneath side of the floating roof of the tank.
8. Check the roof pontoons on the floating roof for vapors and clean/ vent them if necessary.
9. Check seals on floating roof tanks for the presence of vapors and product.
10. Inspect for cleanliness and the presence of hidden vapors to confirm your tank is clean and vapor free.

Selecting the right equipment

By having the broadest line of specialty services, skilled personnel, and automation capabilities, Thompson Industrial Services recommends the below equipment and benefits for tank cleaning.

1. Camera Manway Cannons
2. Tank Sweeps
3. Two or Three Phase Centrifuges
4. Tank Cleaning ROV
5. Tank Cleaning ROC
6. SRS (Solids Reduction System)
7. Filter Press

Read more about the different equipment options available and help you choose the right equipment for your tank cleaning project.

Common Hazards & Safety Tips

The ultimate goal of cleaning your tank is to provide a safe environment for whoever is entering the storage tank for repairs and inspections, and to make sure your tank is running safely and properly.

Tank cleaning has the potential to be very dangerous. The nature of tank cleaning involves working in confined spaces combined with the contaminants that remain inside the tank that can increase the risk of fire, explosion, chemical exposure, and more.

Below are safety tips in regards to tank cleaning:

• A plan should be created and reviewed by all participating personnel, including tank cleaning procedures and potential risks.
• Medical kits and a confined space rescue team should be on standby.
• Only trained professionals should attempt to clean a storage tank.
• Professionals should be certified and follow OSHA tank cleaning procedures.
• Professionals must be protected using the correct PPE including hard hats, eye protection, respiratory protection, body suits, harnesses and retrieval lines.