Cleaning and disinfection of stainless steel tanks

Maintenance secrets to extend the life of your tanks

Do you have stainless steel tanks? If so, you'll know that good maintenance is essential to ensure their longevity. Stainless steel tanks play a crucial role in various industrial sectors, such as chemical manufacturing, brewing, the food industry and many others. In this article, we'll be giving you some in-depth advice on how to keep your stainless steel tanks in top condition and extend their life. By following these recommendations, you can not only save time and money, but also ensure a safe and efficient production environment.

Stainless steel is renowned for being the most corrosion-resistant metal, widely used in the manufacture of cable management systems and many other industrial applications. There are different grades of stainless steel, each offering a specific level of protection. However, contrary to popular belief, even stainless steel can be prone to rust if not properly installed and maintained. In this article, we'll give you an overview of the specifics of stainless steel and explain how to clean and maintain it, and maintain its corrosion resistance to ensure the longevity of your installations.

an overview of stainless steel

To maintain your stainless steel installations properly, it's vital to understand why this material is so popular. Unlike many other metals that are susceptible to corrosion - such as iron or mild steel, which quickly turn orange/yellow in the presence of oxygen - stainless steel stands out for its resistance. Metals such as iron are said to be ‘active’ because they react with oxygen to form rust on a continuous basis.

Stainless steel, on the other hand, is considered a ‘passive’ metal. This is due to its composition, which includes stabilising elements such as chromium and nickel (for type 304 - 1.4301 - V2A stainless steel) and molybdenum (for type 316 - 1.4404 - V4A). During the manufacturing process, a thin layer of chromium oxide forms on the surface of the steel thanks to a reaction between the chromium and oxygen.

This protective layer, although microscopic and invisible to the naked eye, is capable of regenerating itself, giving stainless steel its impressive resistance to corrosion. As long as this barrier remains intact, the surface remains ‘passive’ and stainless. However, if this layer is damaged, it begins to reform rapidly. There is, however, a short period of time during which the exposed surface becomes ‘active’, and direct contact with contaminants can trigger corrosion.

It is therefore essential to follow certain good practices to minimise the risk of corrosion and ensure the durability of your stainless steel installations.

→ Read the detailed article on stainless steel

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why is the maintenance of stainless steel tanks crucial?

The three fundamental principles of stainless steel tank maintenance

To ensure the durability and performance of your stainless steel tanks, it is important to focus on three key aspects of maintenance:

Frequent and appropriate cleaning
The first line of defence against corrosion and contamination is regular and proper cleaning. Use cleaning products specially designed for stainless steel and follow the tank manufacturer's instructions for best results.
Regular inspections
Frequent inspections can detect signs of corrosion, leaks or other potential problems at an early stage. Early detection makes it easier to solve problems before they become more serious.
Preventive maintenance
In addition to cleaning and inspection, it is crucial to establish a preventive maintenance programme. This includes the periodic replacement of seals, valves and other components subject to wear, to ensure that the tanks remain in good working order over the long term.

In short, maintenance of stainless steel tanks is an essential process that goes far beyond simple cleaning. By adopting rigorous maintenance practices - combining proper cleaning, regular inspections and preventive maintenance - you not only ensure the longevity and efficiency of your equipment, but also the safety of your operations and the quality of your products. Not neglecting these aspects can prevent costly complications and unplanned production stoppages, ensuring that your plant runs smoothly and reliably. Investing time and resources in proactive maintenance is a worthwhile strategy for preserving the value and performance of your stainless steel tanks.

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maintain exemplary microbiological quality

The microbiological quality of wines is a key element that relies heavily on the cleaning and disinfection methods used in winemaking equipment. Fermentation and storage tanks, in particular, are crucial to ensuring this quality. In this section, we detail the best practices for cleaning and disinfecting tanks, focusing on the critical steps to follow to ensure impeccable hygiene.

Cleaning doors and tank seals

One of the most important aspects of tank cleaning concerns the doors and, more specifically, the door seals. Often neglected, these seals can quickly become breeding grounds for bacteria. Wine can seep behind the seals over time, creating an environment conducive to the development of acetic bacteria, responsible for undesirable tastes that can alter the quality of the wine. To avoid this, it is vital to carefully clean and disinfect the doors and their seals. It is often necessary to dismantle the seals and soak them in a cleaning solution to eliminate all residues and micro-organisms, particularly if the seals are worn or ageing.

Valve maintenance: a key point

Tank valves, whether ball or butterfly, also require special attention. Scale deposits can build up inside them, complicating cleaning and creating potential niches for undesirable micro-organisms. For effective cleaning, it is advisable to dismantle the valves before each new winemaking campaign. This operation should include brushing, descaling and disinfecting the valves, as well as soaking them in an appropriate cleaning solution to ensure that all impurities are removed.

Cleaning the tasting tap and internal components

Tasting taps and other internal tank components also require meticulous attention. They can accumulate scale and wine residue, compromising overall hygiene. Before any use, these components must be dismantled, cleaned, disinfected individually, and soaked if necessary. When a tank is empty, the use of a swab to clean the inside of the tap, particularly the parts inside the tank, is strongly recommended.

Maintenance of the upper parts and the aseptic belt system

The upper areas of the tanks, such as the lids, should not be neglected and require thorough cleaning. The aseptic belt system is often used to limit exposure to air and prevent the growth of bacteria and mould. It is essential to ensure that all surfaces are thoroughly cleaned and disinfected. For large tanks, the use of sulphite-based solutions can be effective in maintaining an aseptic barrier.

Optimising cleaning by using nitrogen

Some modern installations use nitrogen to purge air from tanks, eliminating the need for an aseptic belt. The nitrogen expels the air, reducing the risk of microbial contamination. In addition, special valves are often installed to facilitate the injection of water or cleaning products into the pipes, ensuring effective, thorough cleaning.

Although rinsing tanks after emptying is common practice to save water and time, it is strongly recommended to carry out complete disinfection after rinsing and just before refilling to ensure optimum hygiene.

Rigorous cleaning and complete disinfection of the tanks and their components are essential to maintain the high microbiological quality of the wine. Every step, from maintaining door seals to cleaning valves and taps, is essential to prevent microbial contamination and ensure top-quality wine production. By following these best practices, wineries can protect the integrity of their wines and ensure an excellent end product.

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✓ good practices for maintaining stainless steel tanks

By applying the good practices below, you can keep your stainless steel installations in excellent condition for many years to come.

Using the right tools: To clean stainless steel surfaces effectively, choose non-abrasive tools. A soft cloth or a plastic abrasive pad is ideal for preserving the passive protective layer of stainless steel. If you use stainless steel abrasive pads, always do so in the direction of the original polishing marks to avoid damaging the surface.
Respect the polishing grain: Some types of stainless steel have a visible polishing grain. In these cases, it is essential to always clean in the direction of the grain. If the grain is not visible, use a soft cloth to avoid scratching the surface.
Choosing the right detergents: Choose alkaline detergents, chlorinated alkaline cleaners or chlorine-free products. Most cleaning products available contain chlorides, but chlorine-free alternatives are now more accessible. If you are unsure about the chlorine content of your usual detergent, consult your supplier or the manufacturer for an alternative. Avoid cleaners containing quaternary salts as they can corrode stainless steel.
Regular disinfection: Once the stainless steel is clean, it is important to carry out disinfection or sterilisation (if necessary) to remove any potential contaminants. Use an appropriate disinfectant in accordance with local regulations. Pay particular attention to detail to ensure that all surfaces are thoroughly disinfected.
Water treatment: Although it's not always easy to do, softening hard water can reduce the formation of deposits on stainless steel surfaces. There are various filters available to remove corrosive and undesirable elements. To ensure effective water treatment, call in a water treatment expert.
Keeping food processing equipment clean: Use alkaline cleaners, chlorinated alkaline products or chlorine-free cleaners in the recommended concentrations. Clean regularly to avoid the build-up of stubborn stains. If you boil water in stainless steel tanks, be aware that the chloride in the water is often the main cause of material degradation. Heated cleaners containing chlorides have a similar effect.
Rinse and Dry Correctly: If you use chlorinated detergents, be sure to rinse and dry the stainless steel surface immediately with a clean cloth. The sooner the chlorinated water is removed from the surface, the better. Allow the surface to air dry, as oxygen helps to restore the protective passive oxide layer. In environments where standing water cannot be wiped off (such as marine or offshore environments), the use of high-grade 316 - 1.4404 - V4A stainless steel is recommended because of its increased resistance to corrosion.
Avoid Hydrochloric Acid: Never use hydrochloric (muriatic) acid on stainless steel. This reducing acid lacks the oxidising properties necessary to maintain the passive protective layer on stainless steel. Its presence in the environment can cause rapid corrosion.
Improving Ventilation in Chlorinated Environments: If your stainless steel equipment is installed in an environment where chlorinated condensation is present, such as swimming pools, it makes sense to improve ventilation around the installation. This reduces the risk of rust pitting and staining. We also recommend using type 316 - 1.4404 - V4A stainless steel in these conditions.
Restoration and Passivation of Stainless Steel: Stainless steel can naturally restore its passive protective layer when its surface is exposed to a sufficiently oxygenated environment, promoting the formation of chromium oxide. This anticorrosive property is generally activated by normal exposure to air and aerated water. In some environments, however, manual passivation may be required to enhance this protection.

✗ factors to avoid when protecting stainless steel

Stainless steel, although very resistant, has a few ‘enemies’ that can compromise its protective layer and encourage corrosion. By following the good practices we have shared in this article, you can minimise the risks associated with these factors.

Chlorides and chlorine: Chlorides are often present in industrial and domestic cleaning products, and chlorine is particularly common in environments such as swimming pools. Contact of stainless steel with chlorides or exposure to atmospheric chlorine can alter the steel's ‘passive’ protective layer. However, by adopting appropriate cleaning practices, this risk can be significantly reduced.
Mechanical abrasion: Damage caused by mechanical abrasion occurs when the steel surface is scratched by wire brushes or steel wool pads. To avoid such scratches, which can damage the protective layer, we recommend using soft cloths and plastic pads, which are less abrasive alternatives.
Hard water: Hard water, which contains a high level of soluble minerals, is common in many parts of the world. This ‘hard’ water can leave limescale deposits on stainless steel, and when these deposits are heated, they can degrade the passive layer and lead to rusting. Using treated or softened water is an effective measure to avoid these problems.
Surface deposits: It is crucial to remove all food residues and waste from the surface of stainless steel after processing. These deposits can not only affect the appearance of the steel but also contribute to the degradation of its protective layer.

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To extend the life of your stainless steel vessels, it is essential to understand the fundamentals of care and maintenance. Although stainless steel is renowned for its corrosion resistance and strength, inadequate or insufficient maintenance can reduce its performance and lead to problems such as corrosion, contamination and premature wear.

By following rigorous cleaning practices, carrying out regular inspections, and putting in place a preventive maintenance programme, you can not only ensure that your equipment runs smoothly, but also maintain optimum microbiological quality, particularly in the production of wine or other sensitive products. What's more, choosing the right tools and products, and taking environmental factors into account, are crucial to protecting stainless steel's passive layer, which is the key to its durability.

Finally, by avoiding factors that can compromise the natural protection of stainless steel, such as chlorides, mechanical abrasion, hard water and surface deposits, you minimise the risk of corrosion and preserve the quality of your installations. By investing in regular, appropriate maintenance, you can guarantee not only the longevity of your stainless steel tanks, but also the safety and efficiency of your industrial operations.