5 Things You Need to Know About Food-Grade Stainless Steel

Mar. 07, 2024

For sanitary food handling applications, stainless steel is a popular material choice. Not only can food-grade stainless steel stand up to punishing temperatures that would melt plastic, the material’s protective oxide layer helps prevent the formation of rust that could contaminate foodstuffs.

But, as with any material, there are a few things that you should know about food-grade stainless steel before you implement it in your production process.

1: The Steel’s Finish Can Affect its Suitability for Food Processing

Stainless steel is famous for being able to resist corrosion, but just because the surface of the steel looks shiny and smooth doesn’t mean that it’s food-grade.

To meet key sanitary standards, the finish of the steel MUST eliminate any surfaces that could result in bacterial growth while being easy to clean/sanitize.

Here, processes such as electropolishing are favored over manually grinding down surfaces. The reason for this is that electropolishing strips away the surface layer of steel to reveal a microscopically-smooth substrate.

This not only enhances the strength of the oxide layer in stainless steel; it removes the microscopic flaws in a surface that could harbor bacteria.

2: Stainless Steel Should NEVER Be Cleaned with a Plain Steel Brush

Steel wire brushes are a popular choice for cleaning deep-set stains from metal surfaces. However, such brushes should NEVER be used to clean a stainless steel object.

Particles from the plain steel in the brush could become imbedded in the surface of the stainless steel, compromising the integrity of the protective oxide layer. Over time, this will allow the “stainless” steel to rust like ordinary steel.

Additionally, you should avoid using the same tools to clean both stainless and ordinary steels. Particles picked up from the plain steel could transfer to the stainless.

3: Not All Food-Grade Stainless Steel Alloys Are Created Equal

Just because a steel alloy is marketed as being “food grade” doesn’t mean it’s the right material for your production process.

There are a number of different stainless steel alloys on the market, each with its own strengths and weaknesses when it comes to resisting specific chemicals and production environments.

For example, salt is known for being exceptionally corrosive to metal compounds. While grade 304 stainless steel is resistant to most corrosives, prolonged exposure to salt can still eat away at it. So, grade 304 stainless wouldn’t be suitable for any process requiring repeated, prolonged exposure to salt or saltwater.

Grade 316 stainless, on the other hand, is much more resistant to salt exposure than grade 304. This makes grade 316 stainless steel preferable for food makers that use salt or saltwater in their products.

4: Temperature Extremes CAN Affect Food-Grade Stainless Steel

Most stainless steels have a melting point well outside of the temperature ranges typically employed in any food manufacturing process. However, it is still important to be careful of temperature extremes in your manufacturing process when selecting a food-grade stainless steel (and any potential coatings for it).

For example, most formulations of stainless steel are fine at temperatures ranging from the freezing point of water to oven-like temperatures in excess of 500ºF. However, according to Gasparini Industries, truly cryogenic conditions below -49ºF can cause many stainless steel alloys to become brittle. This, combined with crystalline expansion as metals heat up, can cause these metals to warp or break if exposed to sudden extreme temperature shifts.

Among stainless steels, martensitic stainless steels tend to handle extremely low temperatures the best. This is because the structure of martensitic stainless steel is less susceptible to becoming brittle when exposed to low temperatures.

Additionally, it's important to consider the risk of oxidation when using a food-grade stainless steel alloy in high temperatures. For such applications, grade 304 stainless steel is often useful because of its ability to resist oxidation at temperatures of up to 1,697ºF. This is well over the limit of virtually any food manufacturing process (outside of sterilizing baskets between uses).

5: Welding Can Alter the Properties of Stainless Steel Alloys

The heat stress applied during some welding processes (as well as the use of dissimilar filler materials) can strip the protective oxide layer that gives food-grade stainless steel alloys their resistance to corrosion. This, in turn, can make metal forms that have been welded improperly start to corrode faster than they should.

This is why Marlin's engineers use a resistance welding method applied via a high-precision medium frequency direct current (MFDC) machine. Because the machine can accurately complete welds without excess heat or filler material, the risk of altering the protective oxide layer of the steel being welded is minimized.

Getting to know the strengths and weaknesses of stainless steel prior to implementing it in your food production process is critical for ensuring safety, sanitation, and efficiency. Learn more about stainless steel from the experts at Marlin Steel today!

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Stainless steel alloys are popular for applications big and small across numerous industries.

There’s a good chance that there is a stainless steel product or piece of stainless steel equipment within a short walk of where you are right now.

But if you’re looking to design a system, create stunning designs, or fabricate parts and equipment, you’ll have to start with basic stainless steel products and work from there.

In this guide, we’re going to look at the most common stainless steel shapes and sizes you’ll encounter and the considerations you should make when determining the ideal product for your next project.

Formats Explored: Stainless Steel Sheets, Plates, and Bars

Before we dive into the various characteristics of alloys, finishes, and other more metallurgic details, we should explore the different shapes and formats in which stainless steel is sold today.

Each will offer different benefits depending on your intended use.

As such, understanding your options can help you to find a format that is most closely matched to your needs and avoid additional costs and time spent on further processing before you can use your stainless steel.

Stainless Steel Sheet

Stainless steel sheet is the most flexible option in most cases–both in terms of sizing and shape and in your ability to form it to fabricate products or meet your design specifications.

Depending on your needs, you’ll find stainless steel sheets in thicknesses up to around 6mm.

Products above this thickness tend to fall into the plate form instead.

If you’re sourcing your sheet from the U.S., you might also find this thickness listed by gauge instead of in millimeters.

In most cases, the stainless steel supplier will offer a range of standardized sizes.

Common sizes include 48-inches-by-120-inches (roughly 122-centimeters-by-305-centimeters), 60-inches-by-120-inches (roughly 152-centimeters-by-305-centimeters), and 72-inches-by-120-inches (roughly 183-centimeters by 305-centimeters.)

However, many suppliers can also offer metal cutting services using plasma cutters, waterjet cutters, and other tools to provide a product that precisely meets your ideal size and shape.

Sheet is ideal when you plan to shape or cut the base stainless form to create lighter-weight parts and equipment.

Most sheets are delivered in an annealed state, providing an excellent balance of strength and malleability.

This means you can often take stainless steel sheets directly from shipping to the press for shaping or welding table for fabrication with minimal preparation or pre-processing.

Since the sheet is often cut into standardized sizes, it’s also easier and more space-efficient to store than some other forms.

However, if you plan to stack or store stainless with a mirror or high-gloss finish, be sure to consider any precautions to avoid marring your product's finish before use.

Stainless steel sheet is commonly used in the chemical, construction, food service, marine, transportation, and textile industries.

Stainless Steel Plate

Stainless steel plates can share many similarities with stainless steel sheets.

However, it starts at higher thicknesses in most cases and is often smaller in overall surface area.

Plate is also available in standard sizes, though these tend to start smaller–around the 12in-by-12in (or 30cm-by-30cm) range and topping out around 48-inches-by-120-inches (roughly 122cm-by-305cm.)

However, like with sheets, you can also order these with custom cuts and sizes to fit your intended application or any special needs you might have.

Keep in mind that thicker pieces will typically mean greater weight when compared to stainless steel sheets of comparable size.

However, this also means increased strength depending on the need.

Stainless steel plate is commonly used in the chemical, construction, food service, marine, transportation, and textile industries.

Stainless Steel Bar

Unlike stainless steel plate or sheets, stainless steel bar comes in various shapes, including round, square, hex along with angle and flat bar and hollow bar.

Their names essentially refer to their shape, giving an easy way to start limiting choices to find your ideal bar type.

Like plate and sheet, stainless steel bars are available in various thicknesses (or diameters depending on the shape.) Standard sizes range from 3mm to 25mm.

Flat bars are often used to help form base plates and brackets or reinforce key areas where plate might otherwise be a poor choice.

Round stainless steel bars (sometimes referred to as stainless steel rounds) are very popular in machining for creating fasteners, threaded tubes or shafts, and other items.

Hexagonal and hollow bars are often used in weight-bearing scenarios and the fabrication of many common structural beam elements–including I beams, H beams, and C beams. However, hexagonal bars can also have machining uses similar to stainless steel rounds, allowing for rapid production of nuts and other fasteners.

Square bars fit well into both categories, providing excellent structural and load-bearing support while also being an ideal shape and format for machining and fabricating various fasteners.

Other Traits and Characteristics to Consider

Of course, when choosing the ideal stainless steel product for your needs, the actual format is just a part of the overall decision.

You also need to determine the best stainless steel alloy, ideal finishes, and other traits that might impact your components' service life and overall fit for your budget.

Grades to Consider

Most plate, sheet, or bar products will be available in a range of alloys, including those in the 200, 300, and 400 series.

However, you might also find that specialized grades are available for specific uses.

300-series stainless steel will provide an excellent balance of cost, weight, fabrication ability, and corrosion resistance in most cases.

However, 400-series steel is popular in food service applications, medical environments, or when looking for a ferritic stainless option.

If you’re looking for more information regarding the various stainless alloys and their traits, be sure to consult our guide to stainless steel grades and families.

Finishing Touches

Finishes are another consideration that can impact overall costs and better align your stainless steel with your intended use.

For example, mirror finishes (#8) might look impressive but quickly pick up fingerprints and show scratches and other wear easier.

As such, if they’re in a high-traffic or touch-heavy environment, you might spend an unreasonable amount of time maintaining that finish.

You’ll also need to take extra precautions when storing the steel or fabricating and assembling to avoid damage. In many cases, a protective liner is recommended to avoid mishaps.

By contrast, brushed finishes (#4)–popular in food service and appliance use–offer a clean, professional appearance with far fewer cleaning and maintenance requirements.

On the other hand, if you plan to do extensive fabrication or welding, you might find it best to apply a finish yourself.

In these cases, opting for a product with a 1, 2B, or 2BA finish could reduce costs and allow greater flexibility.

For more information, including typical uses and any considerations to keep in mind, be sure to consult our guide to stainless steel finishes.

Fabrication Methods

This final consideration touches on points related to virtually everything considered so far.

If you’re planning to cut, weld, rivet, or modify the steel in any way, be sure to consider any stresses applied to the steel and potential treatments which might be required to return the steel to an ideal state.

For example, extensive welding or the heat of plasma cutting might require you to consider pickling, electropolishing, or other heat treatments to ensure that the passive layer is effectively restored and promote optimal corrosion resistance.

Riveting or fastening will require you to consider any hardware used to minimize galvanic corrosion risks.

Tapping or threading stainless steel bars and other parts will likely require attention to machined areas to ensure complete restoration of the passive layer and avoid corrosion risks.

By understanding these factors in advance, you can avoid maintenance surprises, optimize costs, and pick

Summary

Stainless steel sheet provides a relatively thin stainless product ideal for fabrication and forming.
Typically thickness is measured in millimetres, with sheet topping out around a thickness of 6mm.
Sometimes thickness is listed as gauge or inches instead.
Sheet typically comes in standard pre-cut sizes ranging between 4 feet (1.2m) and 6 feet (1.8m) wide and up to 10 feet (3m) long.
Customized sizes are offered by suppliers with cutting services in most cases.
Sheet is often delivered in an annealed state.
Stainless steel plate is a thicker stainless steel product, often available in smaller sizes than plate due to its increased weight.
This thickness might also limit your custom sizing options due to cutting requirements.
However, the increased thickness can mean increased strength depending on your intended application.
Stainless steel bar is available in a variety of shapes and sizes.
Standard options include flat bars, round stainless steel bars, hexagonal bars, square bars, and hollow bars.
Bars can meet a variety of needs, seeing use across nearly all industries.
Your choice of stainless steel grade can further influence the traits of your stainless steel bar, plate, or sheet.
300-series steels are good all-around options for balanced cost and corrosion resistance.
400-series steels are excellent for ferritic options and are commonly found in food service and medical environments.
Finishes can also play a role in optimizing your stainless steel bar, plate, or sheet choice. Mirror finishes, for example, look great but show fingerprints and wear easier. On the other hand, brushed finishes are fantastic for avoiding smudges, knicks, and marring.
If you’re planning to cut, weld, rivet, or modify your stainless steel in any way, be sure to consider any additional treatments or special methods required to ensure optimum corrosion resistance and strength.
Pickling and electropolishing can help to eliminate the impact of heat exposure.
Taking care to avoid contamination and encouraging passivation can help recover from damage resulting from fasteners or threading.

For more than four decades, Unified Alloys has helped supply industries large and small throughout Canada and North America. If you’re searching for

By understanding these factors in advance, you can avoid maintenance surprises, optimize costs, and pick stainless steel products that are best suited for your uses and environment.For more than four decades, Unified Alloys has helped supply industries large and small throughout Canada and North America. If you’re searching for stainless steel bar, plate, or sheet products , our comprehensive selection and experienced sales analysts are ready to help! Contact us today to discuss your needs.