Case Study
In December 2002, Hydrocarbon Engineering published a case study comparison of out of service inspection verses ROV in-tank inspections. The case study examined a 100 ft. diameter regular gasoline tank, the author said this:
Situation
There is a light product terminal owned and operated by a mid-size company in the Southeast. The company needs to inspect its one 100 ft. diameter regular gasoline tank (common problem since the introduction of the new gasoline grades is not accompanied by additional tankage), which breaks suction to the loading rack at 18 in. Prior to starting the project there are numerous planning and scheduling activities. The terminal operator works through the supply and trading departments to purchase regular gasoline FOB rack at a competitor’s terminal. The traders naturally pay a premium for temporary product coverage since the lot is relatively small and a terminalling fee is imposed. Loading rack customers such as distributors are notified about the temporary product arrangement so their lifting patterns can be adjusted. The engineer begins the coordination process for numerous contractors: providing temporary tanks and pumps, tank cleaning, equipment rental, waste hauling, etc. Terminal operators must also work with dispatch centres since their own trucks will be less productive loading premium and regular at two locations for each delivery. A company trained safety specialist for tank inspection is located for the scheduled cleaning and inspection process.
Out of Service Solution
Obviously we updated the numbers to compensate for inflation and to reflect our operational cost. So here we go; the article continues, The project starts by draining the tank via the loading rack until it breaks suction. The remaining 45,000 gallon consists of 35,000 gallons of saleable product and 10,000 gallons of water/sediment. Since there is nowhere to put the regular gasoline at the terminal, they give it to a waste processing company and pay US$ 0.11/gallon plus freight for disposition. The real cost to the energy company is US$ 0.11/gallon plus US$ 0.75/gallon for the saleable product. During the cleaning and inspection process, the company-owned trucks must load at two sources for each trip. Distributors and other loading rack customers are equally inconvenienced; sometimes they choose alternative sources for supply to avoid the additional logistics cost. Finally, pipeline deliveries need to be juggled since the customer cannot make the regular gasoline off takes. Unfortunately the inspection indicates repairs are required. The repairs are not required immediately but rather than put the tank back in service and clean it a second time for repair, the repairs are scheduled for completion right away. The operator urgently needs the tank back in service so the company waives the bidding process for selecting a tank repair contractor. Instead, they find the first qualified contractor who can start work immediately. The company had incurred significantly higher costs since contractors charge more for emergency requirements, and certain repairs have been accelerated into the current year so that the tank can remain in service for the foreseeable future.”
Robotic In Service Solution
After a brief planning process, the robotic process starts by lowering the robot into the tank. Tank sludge removal is optional for the customer but not required since it is not affecting product quality and does not interfere with the inspection process. The full inspection is completed with a three person crew over a period of four days. The tank stays in service during the entire process. After the data is collected and analyzed, a full engineering report is completed for the tank.
Conclusion
Since the inception of API 653, operators have had just one method for inspecting tanks: the out of service method, which required product and vapors freeing the tank. The out of service method has significant health, safety and environmental ramifications and is expensive once the hidden costs are considered. New robotic methods benefit storage tank management: reducing the health, safety and environmental risk while saving cost. Now that many tanks are approaching the second wave of inspections since the introduction of API 653 tank owners have a new, cost effective inspection tool to tame process costs.