Cleaning And Requalifying Cylinders

Manual vs. Automatic

Everyone likes the look of a nicely painted cylinder, but maybe not what it takes to get that final product. Traditional manual systems using hand-held blasting equipment coupled with a compressor make for a dirty and tedious job. When it is time for requalification or repurposing of a cylinder, abrasive blasting is the most efficient process of preparing it for testing, inspecting, recoating and new service.

There are options to automate internal and external cleaning processes, thereby reducing manual handling of the cylinders.

Blasting the Manual Way
Repurposing of existing cylinders for changeover of service or cleaning for specialty gases can save the expense of purchasing new cylinders. The manual way to do internal blasting includes a system to roll the bottle while an operator blasts the interior with steel shot and blast nozzle on a wand. The process can take up to ten minutes and can leave an inconsistent finish.

Tumbling is another means of removing internal corrosion. Cycle times are several hours long, and tumbling does not clean the neck and bottom of the cylinder.

External blasting of cylinders can be done with a manual blast system with a large nozzle, hose and compressor. This requires turning or rolling the cylinders over. Cabinet-style shot blasters—mechanization not automation—blast large cylinders or multiple cylinders in a basket and can take up to three minutes. This also requires handling of the cylinders multiple times for moving, loading, unloading and moving again. Further steps are necessary if testing hydrostatically with evacuation of gas and removal of the valve prior to pressurizing. The risk with this process is damage to threads and valves. An upside is the low investment required.

Shot blasted cylinder

Shot blasted cylinder ready for testing or coating

Automation ROI
Automation of the internal blasting is done with motor-driven lances and Programmable Logic Controllers (PLCs) that control rotation and travel speed of the lances. Conveyors or robots can place cylinders into position for blasting. Specially designed nozzles are used for blast coverage of all surfaces. Custom programs can be used for multiple cylinder sizes and can control the entire process from the neck to the side and then to the bottom of the cylinder. The automated cycle is faster, with a processing time from one to two minutes on multiple cylinders all with a consistent surface finish. A wash system can follow to further evacuate all particulate and then purge with dry gas to remove any water and oxygen.

Automation of refurbishing or requalification includes a PLC and integration of conveyors, an external shot blaster and ultrasonic testing systems. There are several process models that can be used in automation.

One process begins with the operator noting the cylinder identification number and loading the cylinder onto the infeed conveyor. The cylinder is indexed to the automated shot blaster. After a 20-90 second blast cycle, the cylinders accumulate on the outfeed conveyor. Following this, the cylinder is indexed to the test system. After testing, the operator checks the results to determine pass, fail or retest status. A visual inspection can then be done if necessary before stamping of the new test date in the cylinder.

A second process includes the infeed conveyor, automated shot blaster, outfeed conveyor and accumulation table. The operator enters the cylinder number, does a visual inspection, load and test.

An advantage of these two processes is that the valve is left in place. Both processes allow for cylinders that bypass the testing step. Cylinders can then be recoated (manually or automated), filled and put back into service.

The Bottom Line
Automation may take an initial investment that at first glance seems daunting. But when you consider the time required to manually clean and test, it is worth taking a thorough look at automating the process. Higher rates of production and additional service time with like-new cylinders provide a quicker return on your investment.

Gases and Welding Distributors Association
Britton Harper Meet the Author
Britton Harper is cylinder product manager at LS Industries, located in Wichita, Kansas, and www.LSIndustries.com.