These Technical Frequently Asked Questions aim to assist our customers with basic understanding and solutions to some on-hand technical difficulties anywhere at anytime.

email : technical@poscothainox.com
Q:
When using for a long time an electric pot or a kettle to boil water, white deposit of tartar appears inside the pot or the kettle. Why can’t it be removed through cleaning? If then, how can it be cleaned?
A:
The white deposit appeared because of water quality.The solid carbonate formed because of the hardness of water. The hardness of water refers to the quantity of salt, calcium and magnesium dissolved in the water. To clean the white deposit, one can use vinegar to remove it. If it sticks strongly, one should use vinegar with water and boil it about 10-15 minutes.
Q:
When using flour mixing bowl made of stainless steel to steam pork legs with sauces and herbs and to warm them for the whole day, may one see its bowl cracking and contents leaking?
A:
For steaming pork legs in sauces and herbs with soy beans for the whole day, if boiling temperature is less than 150 degree C, it should have no effect. But it may affect stainless steel if improper cleaning after using or keeping steam pork legs for 2-3 more days (to be sold).
Q:
Would heating at a temperature superior to 400 degree Celsius for a whole day change stainless steel properties ?
A:
It may affect the properties of stainless steel due to high operating temperature. It is not recommended to use 340 – 600 degree Celsius for 430 grade and 650 – 980 degree Celsius for 304 grade as the carbides will participate and the corrosion resistance will be reduced.
Q:
Why does food stick on the pan when cooking or frying?
A:
It is because of poor and uneven conduction of heat. Manufacturers overcome this by giving pans a three or five-layer sandwich base containing highly conductive metals such as aluminum or copper.
Q:
Why is there a rainbow color after few days of use of a boiling pot ? It can be cleaned but it reappears again when using. Is it dangerous for health? Why does it happen only inside the pot and not outside? Can we assume this is an overheating problem and if so, what is the maximum temperature and time of boiling?
A:
Overheating or letting a pan boil dry will cause bronze, blue or rainbow tints on the stainless steel surface. Although harmless to health, these tints can spoil the appearance of the pan and should be removed with Stainless Steel Cleaners.
Q:
When using Scotch Brite to remove food stains on stainless steel pot or pan, will the thickness of the pot or pan be reduced ?
A:
It should not reduce the thickness of stainless steel pot or pan. However, it is not recommended to clean stainless steel with steel wool in order to avoid scratches.
Q:
Why does stainless steel sometimes rust? It is a common belief that “good stainless steel should not be rusty.”
A:
There are several possible reasons for an appearance of red rust. Rust may incur when steel or iron scratched the stainless steel surface and particles became embedded in the surface. As such, stainless steel should never be cleaned with steel wool. Steel, cast iron, and a fluid with a high concentration of chlorides (most dishwashing detergents) that was left on the stainless steel surface for a prolonged period of time can also create rust to the stainless steel as well. Thus, applications that are made from a less corrosion resistant stainless steel must be well taken care of, kept clean, and avoid prolonged standing water.

In most cases, light staining can be removed with a fine abrasive cleaner or non-metallic abrasive scouring pad. Some of these products will scratch the finish. To minimize the damage, try to apply the cleaning product in the same direction as the polish. Products that are safe for cleaning glass or automobiles are less likely to damage the finish. Many kitchen cleaning products and stainless steel cleaners contain chlorides and should be thoroughly rinsed off after cleaning (www.sensationalstainless.com). Anyhow, stainless steel is not entirely stainless – it will discolor, stain, or spot if left in contact with hard water, salt water, lemon, vinegar or even some detergents if not rinsed and dried carefully after washing. Small pits may form. Care clean with hot, soapy water, using a nylon scourer if necessary. Avoid bleach or harsh abrasives. Soak burnt-on food. Remove stubborn stains with a stainless-steel cleaner (Christine McFadden, The Essential Kitchen).
Q:
Why do the arc welding spots in pots and/or coolers usually corrode?
A:
The acid-base resistance of stainless steel depends on the substance or medias and its concentration. However, in general, 304 grade has higher resistance than 430 in most of the media.
Q:
What is the acid-base resistance of 304 and 430 grades?
A:
The corrosion resistance of welding point may reduce, especially in the HAZ area. This also depends on the welded quality. The welding area should undergo proper treatment by post-heat and cleaning of welded point.
Q:
When a stainless steel container such as a mug is put in a refrigerator, why does its bottom swell ?
A:
The bottom of mug is swelled because of the heat expansion and heat transformation of steel.
Q:
Why is there a yellowish deposit on Sun Brand pan when heating with oil ?
A:
The bottom of mug is swelled because of the heat expansion and heat transformation of steel.
Q:
Is there any temperature effect in cooking to the 304 and 430 series?
A:
There is no any temperature effect to the 304 and 430 series under normal cooking.
Q:
Does any kind of food affect stainless steel ?
A:
Most kinds of food have no effect on stainless steel unless they contain salty sauce, like fish sauce, or have a high concentration of vinegar: it could reduce the corrosion resistance of stainless steel.
Q:
What will effect to stainless steel in each type of stove or oven like gas stove, electric oven, charcoal stove, magnetic stove? And which one is better?
A:
It depends on the heating method used in each type of stove. However, magnetic stove can be used only with some grades.
Q:
Does chlorine in tap water affect stainless steel?
A:
Normal chlorine level is up to 2 ppm for 304 and 5 ppm for 316 series but shock dosing for sterilization purposes, say 25-50 ppm for 24-48 hours, is fine if thoroughly flushed afterwards. As such, we can say chlorine in tap water does not have any effect on stainless steel. It is recommended to keep stainless steel products in dry condition after cleaning.
Q:
Are stainless steel containers suitable for fruit juice or wine?
A:
Tartaric, acetic, tannic, malic, lactic and citric acids are not corrosive to either types 304 or 316 stainless steel series at the concentrations found in juices or wines. However, type 304 resists corrosion when fully immersed at free SO2 levels up to 700 ppm SO2 in the liquid on vapour space (NIiDI).
Q:
Does thickness of stainless steel affect to color mark, water stain or corrosion?
A:
There is no relation between thickness and those of neither marks no corrosion resistant.
Q:
How to prevent or clean black or yellow deposit on stainless steel product, especially gas stove?
A:
Firstly, try soaking the pot in hot water with dishwashing detergent.If this does not work, try adding water to the pot and bring it to a boil. Sometimes this will break up the food deposit. If all else fails, use a mild abrasive scouring powder or non-metallyic or stainless steel scouring pad to remove stubborn deposits. These may scratch the surface. If there are obvious polishing lines, try to rub in the same direction as the lines to minimize surface finish damage.
Q:
What is the cause of fungus on stainless steel containers that have never been used or have been well kept? How can we solve or prevent this problem?
A:
Check production process if using Organic oil or Non Organic oil. Fungus can grow on any location that contains 1) Polysaccharide, 2) humidity and 3) right temperature. In this case, fungus can be occurred by many factors such as Polysaccharide that come from the production process, paper dust (Cellulose) that stay on top of stainless steel surface, humidity and stale atmosphere. These factors make the fungus spores in the air grow faster and larger. Food or snack that staff eat during the packing process can also create the residence on stainless steel surface.
 
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