Apr Newsletter
VOLUME 27 NO. 4Corrosion in fryers and fryer piping is a major concern for french fry potato processors. For most applications, carbon steel is the material of choice for french fry fryer kettles and piping. In the normal operating/cleanup cycle, the steel is subjected to significant temperature changes and rather harsh chemicals. As a result, after a few years in operation, leaks develop in most french fry potato frying systems. Crawl under a fryer that has been in operation for 10 to 15 years and you will probably see some fist sized blocks of polymer, a black plastic like substance. There is one benefit from the oil forming a “plastic.” The polymer formed often plugs the leak. One of the oils that the industry recently started using does not form a polymer at the outlet of the leak. With this self sealing factor eliminated, the oil keeps leaking out. This may be one reason the industry is becoming more concerned about leaks caused by corrosion.
Regardless of the reason, the french fry potato industry is placing a much higher priority on eliminating the possibility of oil leaks developing in the frying system. Cleanup chemicals play a major role in the corrosion that causes the leaks. Normal cleanup procedure is to boil-out the fryer with a caustic solution that cleans oil and food particles out of the system. Then an acid solution is circulated through the system to neutralize the caustic. Water is then circulated through the system to wash out the acid. According to one chemist, the acid causes the corrosion. Any opening in the surface, such as a crack, a pinhole in a weld or a depression, will trap acid, which eats away at the metal. While most of the corrosion shows up at welds, leaks have been observed well away from the weld and heat affected zone surrounding the weld. At least one example has been observed where the heat affected zone corroded away and the weld survived. Not all frying systems suffer the same amount of corrosion. There are variations in cleanup procedures and chemicals used. Welding procedures also affect the system’s corrosion resistance.
While Gem Equipment cannot do much about cleanup chemicals and how they are used, manufacturing procedures have been, are being and will continue to be evaluated. Welds in piping is one area that has received considerable attention. Ideally, the surface of the weld inside a pipe should be flat and level with the inside of the pipe, similar to the surface of a weld inside a sanitary tubing that has been purge welded. (For purge welding, the ends of the tubing are sealed to hold welding shield gas inside, resulting in a smooth clean weld inside the tubing.) If the weld does not have full penetration, there will be an opening on the inside of the weld, which will collect acid. The opposite condition occurs if the weld is built up on the inside of the pipe. If the pipe is horizontal, the weld will form a dam at the bottom of the pipe. This dam, while not as detrimental as a crack or pinhole, can trap chemicals that cause corrosion. For this reason, Gem Equipment does not recommend Xray quality welds in fryer piping. To meet the requirement for Xray quality on an 8 inch pipe, the weld is built up 3/16 inch on the inside of the pipe. To achieve the correct weld configuration on the inside fryer piping, this company is now using a new camera to inspect the welds from inside the pipe.