Whether cleaning a tank after it has been manufactured, before it receives passivation, or in preparation for hauling a product, achieving pristine results is the optimum goal, speakers pointed out at the National Tank Truck Carriers Tank Cleaning and Environmental Council meeting March 30-31.
Discussing cleaning procedures and equipment were George Lyon of Cleaning Solutions Inc, Craig Brown of Stork Materials Technology, and Paul Winniczuk of the University of Florida.
Lyon emphasized that all tanks require a thorough cleaning after they are manufactured and before they are put into service, as well as before passivation is applied. “The most important thing to do before passivation is to be sure a trailer is clean,” he said.
Brown said that before passivation, the tank surface has to have anything organic removed. For best results, the surface must receive uniform treatment. If the surface has been subjected to scratching, rubbing, or grinding, it requires restoration before it can be passivated.
Ethylenediaminetetraacetic acid (EDTA) and citric acid are more environmentally friendly and can be effective passivating solutions.
A portable passivation unit can be used to recirculate the passivation solution in the tank for about 15 minutes, “maybe a little longer, if the tank is really rusty,” Lyon added.
Brown also noted that exposing the tank to the solution for more than 30 minutes doesn't improve surface protection. A final thorough rinse is then conducted.
Applied passive film, basically an invisible substance, adds to the corrosion resistance of stainless steel by oxidizing the surface metal and reducing acid. Passive film forms naturally and instantaneously in air, Brown pointed out.
Having emphasized the importance of tank cleanliness before passivation, the discussions turned to foodgrade tank cleaning. Winniczuk discussed a study he conducted at the University of Florida that focused on specific foodgrade cleaning using a tank developed for the study. The vessel's body was converted to a see-through tank for viewing the clean-in-place (CIP) system used in the project.
In 2008, Winniczuk made a presentation on the study's initial findings at that Tank Cleaning and Environmental Council meeting. This year's discussion centered on the completion of the project.
From the results of the study, Winniczuk determined that certain areas of the tank studied were susceptible to inadequate cleaning, especially in the bulkhead. He also noted that if the CIP device is off-center slightly and the pitch not correct, cleaning is not as effective. When a 90-degree elbow was installed in the CIP system, the tank studied appeared to receive more coverage at the bulkhead.
Winniczuk also advised tank cleaning managers to monitor the amount of detergent used in the cleaning process to avoid residue. When rinse water with low temperature was applied in the tank tested, no soap scum was detected. Wash cycle times must be accurately calculated, and the relationship of water flow rates to pressure should be appropriate, he said.