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Recommended Principles for Coil Design in Hot, Corrosive Environments
Corrosives in Food Manufacturing Facilities
Some of the most common sources of corrosion in food processing plants include:
Acids found in meals
Cleaning products contain chemicals.
Water and steam from manufacturing processes
Acids in Food
A variety of foods and beverages can cause metal food processing equipment to corrode over time. Soups, meats, beans, and cheeses are typically mild to moderately acidic, with pH levels ranging between 4 and 6. Tomatoes, salad dressings, vinegar, citrus juices, and cola are some of the most well-known enemies of metal food processing equipment. Acidic cured meats like pepperoni and salami are also common. These compounds will corrode in the presence of oxygen.
Cleaning Items Including Chemicals
Every food and beverage production must prioritize public health and safety. With several high-profile product recalls in recent years, and as the food processing sector grows and modernizes, regulators have placed an obviously high priority on ensuring that food processors are not making people sick. This level of inspection and oversight has resulted in initiatives such as improved cleaning techniques and stronger detergents, among others.
Several of the chemicals used to sterilize food processing equipment can cause corrosion. These cleaning products contain a variety of components that can be basic, such as sodium carbonate and bleach, or acidic, such as citric acid or sodium citrate, both of which can corrode metals through a variety of ways. Even stainless steel, which is recognized for its corrosion resistance, can succumb to intergranular corrosion when exposed to chlorides.
Water and steam from manufacturing processes
Water and steam are commonplace in most food manufacturing environments, where they are employed for a variety of purposes, including cleaning. High pressure water and steam are frequently used in conjunction with the aforementioned detergents to introduce them to food processing surfaces. Excellent for cleaning, but not very good for preventing rust on equipment.
Corrosion can also be caused by the quality of the steam and water used. The use of corrosive non-condensable steam and low-quality water can introduce additional corrosive pollutants.
The Influence of High Temperatures
In addition to being exposed to harsh detergents and acidic foods, food processing equipment must withstand high temperatures required in operations such as cooking, drying, pasteurization, and others, which are typically performed by heat exchangers.
The temperatures found in food production environments - 650F at the high end - are well within the range of what most steels can bear. But, high temperatures can cause their own problems over time.
Concerns about material integrity are frequently raised at temperatures in this range due to cyclical loading. This happens when equipment is heated and cooled on a regular basis during its service life. Thermal cycling can accelerate the pace at which metals, such as steel, fatigue over time, weakening the metal and perhaps leading to premature failure.
How Vrcoolertech's Experience Can Assist
Thus, by now, you should have a fair notion of the types of situations in which these heat exchangers are put. They're scorching, caustic, and outright hostile to all kinds of machinery. Vrcoolertech has been designing equipment for these settings for decades, and we've learnt a few things along the way. In this section, we'll go over some specifics:
High-temperature design considerations
Corrosive environment design considerations
We've divided these components into two groups for ease of reading, but this Venn Diagram does have a middle area. When both high temperatures and corrosion are present, they can exacerbate the symptoms caused by the other.
High Temperature Design Considerations
Material selection, as is typically the case, has a significant impact on a coil's capacity to survive hostile circumstances.
For example, one of our customers' stainless-steel oven coils failed prematurely, lasting only approximately a year after installation. Following an engineering examination, it was determined that cyclical loading was weakening the steel, resulting in failure at the connection where the tubes met the header.
As a result, we created an improved coil with headers and tubes composed of a super-austenitic stainless steel alloy that could endure high temperatures much better. That switch helped to strengthen certain joints, but it didn't fix the problem entirely.
We designed a tube reinforcement fastened to the coil's high-stress locations to provide further resistance to the impacts of cyclical loading. The tubes were welded to the extra reinforcement before being welded to the header.
We were able to dramatically minimize the frequency with which our customer needed to replace their coils by carefully selecting materials and understanding the forces at work.
Corrosive Environment Design Considerations
We've already discussed how chemicals used to clean food manufacturing facilities can cause metals to rust. While not all of our coils are food-grade, many of the food processing coils we build are compatible with food-grade equipment. Furthermore, regardless of their specialized role, almost all equipment in food processing plants is subjected to regular and aggressive cleaning.
In such instances, we will usually choose stainless steel or a stainless super alloy that can be electropolished before to installation. Electropolishing and other surface treatments aid in the removal of contaminants or impurities from the metal's surface - the objective is to start clean and stay clean. These surface treatments also aid in the removal of burrs and nicks on the metal's surface, which can become a source of corrosion.
Another factor to consider is material compatibility. Our food processing customers frequently want 304 or 316 stainless steel coils, but all-stainless coils are more expensive, and for applications that do not require direct corrosive exposure, various material combinations may be viable. Yet, the use of dissimilar metals in such applications presents the possibility of galvanic corrosion. Contact between metals with different electrode potentials can produce corrosion in the presence of an electrolyte, and food processing factories contain a lot of potential electrolytes, such as food particles.
Even for experienced engineers, food production applications are distinctive and fraught with potential dangers. Vrcoolertech is here to be your experienced partner in the design and construction of heat transfer equipment for food processing. Send us an email if you're changing equipment more frequently than you'd like, or if you'd want someone to take thermal engineering off your plate so you can focus on other issues. We'd be delighted to discuss your application. If you already know what you're searching for, submit a price request and an engineer will contact you shortly.
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