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From our automobiles to our flatware, stainless steel is a tremendously versatile metal found in everyday life. Just like its many uses, stainless steel comes in many forms. The most common in our industry is American Iron and Steel Institute’s AISI classification 304 — or Austenitic stainless steel — which is used in the manufacture of kitchen sinks and accessories; however, it is necessary to know all 304 grade stainless steel products are not created equally.

DIFFERENT CLASSES OF AISI GRADE 304 STAINLESS STEEL

Certainly the most common stainless steel used in sinks is 18/8 — which means that there is 18 percent chromium and 8 percent nickel by weight; 18/10 is another option. The chromium creates an invisible barrier — or passive film — to oxygen and moisture. It fights against most corrosion — or what most would know as red rust. That’s why it is called “stain-less” steel. This layer is very thin and invisible to the eye, and when scratched, it quickly reforms itself. It is very important to remember the chromium content must be 18 percent to ensure adequate safeguards against rust. Equally as important is the nickel content, as it ensures better resistance to stress corrosion or cracking. 

RUST CAUSES AND PREVENTION

Stainless steel sinks can rust, and here are some of the causes and what consumers can do to avoid this from happening. A homeowner certainly does not want to leave a cast iron pot or pan in a sink for any length of time because the iron particles will attach themselves to the sink and cause the appearance of rusting. The best practice for homeowners is to wash the pot, dry it and remove it from the sink. By the same token, they should not open a can of vegetables or soup or the like and leave the empty can in the sink, or the tell tale ring could appear.

After sink use, homeowners should clean it with the appropriate cleansers and dry it after use; this will aid in keeping foreign particles from attaching to the sink and prevent the appearance of rust. Steel wool should never be used to clean a sink since it has a tendency to break apart and leave particles behind that will very quickly rust. Homeowners should also prevent allowing cleaners and abrasives from drying on the surface of the sink, as this can also lead to a degrading of the finish.

What if the sink has never been used, but displays small, pinhead-sized “rust stains” scattered all over it. How could this have happened, obviously the sink manufacturer must have produced a bad sink, right? WRONG. The real reason these rust spots have appeared is due to an installation issue that sometimes gets overlooked.

In order to fabricate the countertop, the installer uses a variety of tools most importantly the use of drill bits and blades made of very hard steel or coated in industrial diamonds. Sometimes after the sink is mounted in the countertop, additional tweaking is needed to ensure the radius or reveal of the sink is accurate. In doing so, blades and bits release small particles of foreign steel attach themselves to the surface of the sink and cause what appears to be surface rust. (Think of the saw dust that comes from a saw when cutting lumber.) Hopefully, when these types of installations take place, the installer knows to immediately clean the sink completely, but sometimes that doesn’t happen, and the customer is left with a sink that needs to be replaced.

OTHER CONSIDERATIONS

Perhaps the install was perfect — and the sink was cared for correctly — and all of a sudden the sink starts to rust. It’s more than likely localized in an area near the drain, or at the side of the sink where the bowl meets the side.

Where could this rust be coming from and why? 

If you recall, we spoke about the metal content of stainless steel. There are certain levels of chromium and nickel needed to ensure the sink is corrosion resistant. Yes, there are standards for 304 stainless, but that doesn’t mean all sinks are being made according to the regulations required by that certification.

The majority of stainless steel sinks are manufactured in China. The Chinese, for the most part, do a fantastic job at this process; however, sometimes the almighty dollar causes problems. The price of steel was at all-time highs over the last year — as was the cost of nickel. Some factories in China opted to use less nickel, or replace the nickel with other alloys in order to make the same margins.

The result? Some sink companies in the United States who shop factories in China on best prices instead of nurturing a long-term relationship with a factory, ended up with sink products below the standard for 304 stainless steel. Due to the lower levels of chromium and nickel, these sinks are prone to corrosion and have caused a lot of controversy in the marketplace.

What does this mean for the consumer? You may have a sink to replace, but for the fabricator it may mean that you should seek out a sink supplier with a solid relationship with an off-shore factory that provides consistent, quality products.