Renovating food storage tanks
Food tanks or cisterns have many uses in the food industry. For example, they are used to store, mix, ferment and transport liquids and other raw materials. Because food is involved, all tanks must be handled and maintained under strict conditions. Food tanks must be whole to avoid contamination and reduce product losses. Even if tanks are made of durable materials and inspected regularly, they can still be damaged. What damage can occur? Does the tank have to be discarded or can it be repaired? It is often possible to repair a damaged tank. How this is done depends on the nature of the damage, the design of the tank and the requirements.
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Materials in food storage tanks
A food storage tank can hold anything from a few hundred to several thousand cubic meters. Some vessels are so large that they act as a pressurized device because of the volume. Tanks in the food industry are often made of stainless steel because it:
- are resistant to corrosion and can withstand both acidic and alkaline substances. For example, juice and wine tanks need to withstand a low pH level
- is easy to clean. The steel surface is smooth and prevents bacterial growth.
- is durable and can withstand tough cleaning routines
- does not affect taste or smell
If a product is particularly corrosive, a coating may be necessary to protect both the tank and the product. Examples of coatings are epoxy and polyurethane. Some tanks may have an enamel coating on the inside, e.g. tanks for beer or wine.
Applications for food storage tanks
Tanks are used in several parts of the food industry. Here are some examples: Dairy industry: Milk tanks are used to store milk and other dairy products. They are often equipped with cooling systems to maintain the right temperature and avoid bacterial growth. Brewing and beverage industry: Tanks are used for fermentation and storage of beer, wine, spirits and other beverages. Storage tanks need to keep beverages under the right temperature until they are bottled. Oil pressing and fat industry: Storage and blending of oils and fats from plants such as sunflowers, olives and rapeseed. Confectionery industry: for storing sugar, syrups and other ingredients for sweets and pastries. They are also used to melt and mix ingredients such as chocolate and other fillings. Fish and meat industry: Tanks are used to store and process meat and fish. Bakery and grain industry: Used to store flour, sugar and water for dough production. Fruit and vegetable processing: For storing fruit juices, purees and sauces.
Common damage to food storage tanks
With proper maintenance, cleaning and regular inspections, many problems can be avoided, but sometimes tanks still get damaged. Some common damages are:
Corrosion: The risk is greatest if the tank is exposed to aggressive chemicals, acids or alkaline solutions. Improper cleaning with chlorine-based cleaners or too prolonged contact with salts can also cause corrosion. Typically, the damage is visible at welds, joints, valves and drainage areas. In the worst case, the corrosion creates holes or cracks that can lead to leakage and contamination. Stress corrosion cracking: Stress corrosion cracking occurs when stainless steel is subjected to tensile stress and simultaneously comes into contact with a corrosive environment (e.g. chlorides). The risk is greater in the brewing and dairy industries where both high temperatures and chemicals are used. The cracks are often invisible at first, but can eventually lead to leaks.
Biofilm: Microorganisms such as bacteria or yeast can form biofilms. This can lead to corrosion and contamination. Erosion: Occurs when liquids or solids flow rapidly through tanks. The movement can create pits and uneven surfaces that become more difficult to clean and increase the risk of bacterial growth and corrosion. Temperature damage: Rapid temperature changes can cause cracks or deform the tank.
Cracking: May occur due to mechanical stress (vibration from stirring or pumping) or temperature changes. Welds and corners are particularly vulnerable. The cracks can cause leakage or contribute to corrosion if not corrected. Failure of welds and seals: Can be caused by poor welding technique or exposure to chemicals. Both problems can weaken welds and seals and eventually lead to leaks.