An automated tank cleaning machine is a machine used to clean cargo tanks such as those found in tank trucks, railroad cars, barges, and oil tankers.[1] Genericized trademarks such as Butterworth machine and Gamajet are often used to refer to automatic tank cleaning machines regardless of their manufacturer.[2]
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Tanks must be cleaned from time to time for various reasons. One reason is to change the type of product carried inside a tank.[3] Another is to allow the tank to be inspected or for maintenance to be performed within a tank.[3]
Automated tank cleaning machines work in a manner similar to an irrigation sprinkler. Hot water forced through a jet nozzle rotates the nozzle. The nozzle's rotation moves the machine through a cleaning pattern.[1] As the water sprays, the liquid is pumped out of the tank.[3] Portable water washing systems are widely used, but tanks that are cleaned frequently may have a fixed system installed.[3]
The Butterworth Type K machine is widely used.[1] This model can clean a tank of up to 10,000,000 US gallons (38,000 m3).[1] It uses water with a pressure up to 250 pounds per square inch (1,700 kPa) and a temperature of up to 250 °F (121 °C).[1] The water jet reaches up to 115 feet (35 m).[1] Depending on the pressure used, a cleaning cycle can take from about 10 to 50 minutes and the machine uses between 15 US gallons (56.8 L; 12.5 imp gal) and 350 US gallons (1,324.9 L; 291.4 imp gal) per minute.[1]
On most crude-oil tankers, a special crude oil washing system, or COW system, is part of the cleaning process.[3] The COW system circulates hot crude oil through the fixed tank-cleaning system to remove wax and asphaltic deposits.[3]
Although machines are often used to wash tanks, a final stage of manual cleaning known as mucking, is usually performed.[2] Mucking requires protocols for entry into confined spaces and the use of airline respirators, protective clothing and safety observers.[2]
Tank cleaning is dangerous in a number of ways. While tank barges can be cleaned in port, shipboard tanks are generally cleaned at sea.[2] This is largely due to risks of fire and explosion inside the tanks.[2]
The first automated tank cleaning machine was invented by Arthur Butterworth and patented in 1920.[4] His goal was to limit the amount of time that workers had to spend inside tanks, and partially relieve them of a dangerous and laborious job.[4] In 1925, Butterworth established a company to market the machine.[4] Standard Oil New Jersey bought the company in 1930, and it later became a subsidiary of the Exxon Corporation.[4]
In 1986, as part of an internal restructuring at Exxon, the Butterworth company was sold to Exxon management.[4] Today the company is privately held, and headquartered in Houston, Texas.[4]