Brand protection and the production of clean, shiny cans are important to customers in the canning industry. Can corrosion not only negatively impacts a company’s image, but it also can impact the safety of the packaged food. Corrosive cans may cause microleakages, which increase the risk of reinfection after sterilization.
The water used for food sterilization must be properly treated so that there is no risk for deposits and corrosion on cans. The chemical products also should protect the sterilizer equipment and cooling system against deposition and corrosion to reduce maintenance costs.
The use of low hardness water reduces the tendency of mineral scale to build up, but increases the risk of can and steel corrosion. Inhibitors based on nitrite, zinc, high concentrations of phosphates, or molybdate have successfully been used in the past to control corrosion under low hardness conditions. The use of these substances, however, has been restricted for environmental reasons.
GE’s Water & Process Technologies developed a line of environmentally friendly molybdate-free (MO-free) water treatment chemicals to greatly reduce corrosion in the sterilizers and pasteurizers used in the food and beverage industry. The FoodPro ST family is intended for use under soft water conditions, where corrosion of food packages and sterilizer equipment can lead to severe problems. It offers equal or better levels of corrosion and scale inhibition than current molybdate-based products tested by GE (which contain heavy metals such as molybdate or zinc), and is more cost-effective as well.
The new FoodPro ST products enable users in the food and beverage industry to improve product quality and protect sterilizer and pasteurizer equipment from corrosion even under soft water conditions, without the need for heavy metal-based corrosion inhibitors.
German Meat Producer
A producer of canned meats and sausages in Germany operated 13 full-water autoclaves (Rotomats). The autoclaves were connected to an open evaporative cooling system to reuse the spent cooling water after each batch. They were heated by direct injection of steam into the recirculation line of the sterilizers. Due to the mixing of steam condensate and process water in the autoclaves, the recirculated cooling water became softer during operation. Calcium hardness in the makeup water dropped from 200 to 80 ppm and was lower in the recirculated cooling water, which over time can lead to increased corrosiveness. The cooling water was treated with chlorine dioxide for microbiological control, which also can contribute to increased corrosion. The water was changed every second weekend to reduce spot formation on the cans and add hardness.
The use of metal ions such as zinc or molybdate as corrosion inhibitors for water treatment is prohibited by local authorities. To protect cans and sterilizer equipment, an inhibitor based on phosphonate and amines was used. The cans, however, showed frequent corrosion and deposits after sterilization, so manual cleaning was required. Cans that were shipped to customers overseas showed significant corrosion and frequently were rejected.
After a thorough analysis of the sterilizers and the cooling system, GE developed a solution from its FoodPro ST line of MO-free corrosion inhibitors. The FoodPro ST8070 was selected to run a field trial at one of the Rotomats.
A Significant Improvement
FoodPro ST8070 provides effective control over corrosion and deposition on the water-wetted section of the production equipment while enhancing the finished product surface appearance. The proper treatment levels for FoodPro ST8070 depends on many factors, including metallurgy, temperature, water chemistry and system needs. The product should be used in accordance with control parameters that GE establishes for a specific application.
This Rotomat still remained connected to the cooling system. Only the process water during the sterilization phase was treated. Although the cooling water was still treated with a competitor’s product, a significant improvement in the appearance of the cans could be achieved. The various types of cans from the trial Rotomat all looked significantly better than the cans from the other autoclaves. They showed less corrosion and less deposition of minerals. This was a notable outcome, considering the water that was in contact with the cans when they left the sterilizers did not contain the new product.
Due to these good results, the meat producer decided to run a full-scale trial on all of the Rotomats and the cooling system.
After a complete change of the process and cooling water, FoodPro ST8070 was added to the cooling water system to adjust the required product concentration. It was introduced as a scale and corrosion inhibitor and dosed automatically to all Rotomats by dosing pumps.
After the first batch, the cans from all Rotomats had no visible corrosion. Brightness and cleanliness were improved and no manual post-sterilization cleaning was necessary.
There was no negative impact on the appearance of the cans and on the condition of the internal surface area that could be observed during the transition period. The protective layer in the Rotomats’ process vessels could be maintained in good condition.
Because the cooling water could be more easily maintained, the frequency for a full exchange of the cooling water could be extended to four weeks.
The company also received fewer customer complaints—even from those overseas. Another benefit is that less manpower is required for manual cleaning, and water consumption has been reduced, which has led to significant savings.
The results of the trial demonstrated that FoodPro ST products provide effective corrosion protection on mild steel equipment and tin cans, even under corrosive conditions. The products lead to improved can appearance and can tolerate higher levels of organic soils in the process water without formation of deposits.
The FoodPro ST line of products is based on a blend of organic corrosion inhibitors and phosphonates. It enables food and beverage industry customers to improve the cleanliness of cans, leads to less required manual cleaning of spoiled food packages and to fewer rejects from can corrosion. It reduces the need for repair and maintenance of sterilizer and pasteurizer equipment, helps users meet discharge limitations and reduces overall water treatment costs.