SESCO Food Service Blog

Welcome to our food service equipment blog.

So...is stainless steel really stainless?

Bill Wickert - Friday, April 13, 2012

The increase in cost and the high volatility of nickel, used in stainless steel production, has caused manufacturers to raise prices, invoke surcharges, substitute plastics where applicable, or source other grades of stainless steel. Our industry is fast changing to create products that will be very durable in the foodservice industry and mitigate the spiraling prices of Type 304 stainless steel. More and more people are talking about stainless steel, they see the surcharges and price increases and now they are hearing about other grades of stainless, like T201 stainless, which many manufacturers are embracing as a substitute for T304. Many of our customers are asking us questions. Some think that T201 is lower quality or similar to T430. This is not true. Here are the facts so you or your clients will not have to speculate. First, let’s start from the beginning.

 

What is stainless steel?

·        Stainless steel is an iron-based alloy that contains a minimum of 11% chromium to make it resist rust, or stain “less” than other steels. Please note the name is not “stain-never”, but stainless and that is precisely what it will do. It will stain less.

·        There are three types of stainless steel;

1.      Ferritic- Magnetic low carbon steels with chromium like 430.

2.      Austenitic- Non-Magnetic Chromium nickel steels like 201, 304, & 316.

3.      Martensitic - (rarely used). Magnetic low carbon steel with 12% chromium & low levels of nickel.

 

What are the types and characteristics of stainless steel?

·        Type 430. This is a magnetic low carbon ferritic stainless steel and it is 83% steel and 17% chromium. It is rust resistant. It is typically used in low cost sinks and tables as well as refrigerators, ranges, and fryers (not the fry pots) as well as in decorative and support parts. Fryer bodies, oven doors, exterior refrigerator and freezer doors are typically T430.

·        Type 304. This is a non-magnetic austenitic stainless steel that is typically composed of 18%-20% chromium and 8%-10% nickel. It has much higher rust resistance than 430. Critical parts like fry pots, boilers, flash pans, evaporators, and other food handling equipment use T304. Imperial fry pots are T304. Ascend sinks and tables, that we stock, are all T304.

·        Type 316. This is also a non-magnetic austenitic stainless steel, commonly called “marine grade” stainless steel. It is used in environments that are highly corrosive. It is composed of 16-18% chrome, 10%-14% nickel, & 2%-3% molybdenum (has greater resistance to corrosion at higher temperatures than nickel).  T316 is for saltwater applications and is an option for steam kettles that are used with high acid products like chili production.

·        Type 201. This is low-nickel, non-magnetic, austenitic stainless steel. It is 16%-18% chrome, 3.5%-5.5% nickel, and 5.5%-7.5% manganese. The manganese provides corrosion resistance and replaces the nickel in a 2:1 ratio. The substantially lower nickel content makes it more reasonably priced than 304, with no loss in resistance to corrosion in most applications.

Most fry-pots are now manufactured from T201 and T202 as are many refrigerators and freezer. It should perform as a suitable replacement for T304 stainless steel.

 

How does stainless steel work?

·        The chromium in the steel combines with oxygen in the atmosphere to form a thin layer of chromium oxide, which acts as a passive film. The chromium atoms and their oxides are similar so they pack tightly together on the surface of the metal forming a layer only a few atoms in thickness. If the metal is cut or scratched and this passive film is disrupted more oxide will quickly form and recover the exposed surface. Essentially it continually “self repairs” itself. It requires oxygen to do this so if the stainless steel is in a low oxygen (think underwater or wet) or poor circulation environment….it could rust. Chlorides (salts, seawater, kitchen cleanser, high acid products, etc) attack and destroy the passive film quicker than it can repair itself. The result can be stainless steel that rusts. That is why a solution of kitchen cleanser in a tub of water in a sink, or a wet vegetable sink in a cold/ damp cooler or prep room will get pitted, have pin hole

leaks and/or rust. Liquid prevents oxygen from reacting with the chromium to make the passive        self-repairing film. In some cases, extreme high heat and high acid environments (kettles in a chili  parlor, onboard ships) require stepping the grade of stainless steel up to Type 316 which has higher resistance to corrosion and pitting.

 

So what’s in the future?

·        The quest to maintain manufacturer’s profit margins and remain competitively priced will drive the use of T201 stainless steel as a replacement for T304 in most food service applications.

 

In Summary - What are the challenges, facts, and opportunities when using T201?

·        T201 is a great “value engineering” opportunity for manufacturers to reduce or contain costs on equipment by substituting it where T304 was formerly used. One manufacturer I talked to said they believe that the increased demand for T201 may have a dampening effect on the rising price of T304.

·        T201 stainless steel provides similar quality as T304.

·        Products made of T304 may become lighter when manufactured from T201 as thinner gauges can be used to attain the same strength. The added manganese used in T201 makes it harder and, as result stronger, than equal gauge thicknesses of T304.

·        T304 and T201 products with similar finishes placed side by side will look identical.

·        T201 has similar stainless steel characteristics (austenitic) as T304. It has a high resistance to corrosion and non-magnetic characteristics. T430 (ferritic) is not nearly as resistant to corrosion (no nickel or manganese) and is magnetic. Note: The old magnet test as a standard of quality still works!

·        T201 stainless steel is harder than T304 so more power and hold-down pressure will be required for deep draw operations. It has greater spring back (memory) when bent. It has more tensile strength than 304. It is more brittle than 304 so it may require thinner materials for extreme bends to avoid cracking and tearing. It can be welded using similar methods as welding 304. T201 is approved for use by ANSI/NSF International Standard for Food Equipment for use in food contact areas.

 

Source Materials: AK Steel data sheets, Allegheny-Ludlum, Outfront Magazine Fall 2005.

 

 

Comments
Post has no comments.
Post a Comment




Captcha Image




SESCO - Specialty Equipment Sales Company | 5705 Valley Belt Road Independence, OH 44131  | 800-222-0558  | Sitemap  | © 2015