1. Which are the main characteristics and applications of the 304 and 316 steels?

The 304 (18%Cr  8%Ni) is the most popular austenitic stainless steel and has an excellent anti-corrosion resistance, great folding capacity and welding. It is a material with a large variety of applications; So many, that can be found in our houses (in knifes and forks, for example) and also in industry, in applications of structural functions. With the 304 steel, places sets, sets of dishes and pans, coffee pots and milkmaids, sinks, ovens and stoves, hampers for clothes washers and others domestic and household-electric utensils can be produced. In the civil engineering, it is used in elevators, in building covering (façades and ceilings).

In the industry it is present in pipes, tanks, reactors, columns of distillation, exchangers of heat, condensers; and many different manufacture industries, as for example, sugar and alcohol, drinks, chemistry and medical drugs industry, nourishing, cosmetics and derivatives of oil. The aeronautical, railroad, naval, paper and cellulose, petrochemical, textile, hospital factories use this type of steel. Also it is used in tanks for transport products (chemical foods and products). To industry applications where the equipments work in potential corrosive environments, the 304L with maximum 0,03% carbon is used.

O 316 austenitic steel (18%Cr  10%Ni  2%Mo) presents best resistance to corrosion under pressure (corrosion that combines usually three factors: aggressive environment, temperature and tension, applied or resulting from the manufacture process) and, most important, best pitting corrosion resistance.

The 316 / 316L are applied in the same type of industry that uses the 304 and 304L kinds. If these two last materials in some environments (especially with chlorides) show pitting or gap corrosion weakness, the 316/316L can be a solution. As an example, we could say that in the first distillation column in alcohol distilleries, where is high temperatures and high levels of chlorides, the 316/316L is necessary. The behavior difference between 316 and 304 comes from the Molybdenum presence in the chemical composition in the 316. 


2. Which kinds of stainless steel are used in food processing industry?

The stainless steel has a wide use in the industry of manufacture, processing, stockage, distribution and preparation of foods and drinks. Depending on the selected type, the stainless steel can be applied in the most of kinds and class of foods and drinks. The majority of the containers, tubing and equipment of stainless steel in contact with foods are manufactured with the 304 or 316 types. The 430 contain 17% of chrome also is wide used in domestic equipment, where the resistance to the corrosion is not significantly important. Depending on the application, types 304, 304L, 316, 316L and 430 can be adjusted for the processing and food handling, considering that in terms of corrosion resistance, the decreasing scale is the following one:

316 series > 304 series > 430 series

If the type of stainless steel is correctly specified, the corrosion will be totally prevented. The condition and finishing of the surface are not the most important factor in the success of the stainless steel application; however, smooth surfaces not only provide a good cleanness but also reduce the corrosion risk.
The types of corrosion that the stainless steel can be susceptible are:

PITTING AND GAP CORROSION - Occurs mostly in water solution containing chloride. Although the attack can occur in neutral conditions, acid conditions and temperature increases promote the corrosion pits and gaps. The pitting corrosion causes extremely long and narrow pits in clean surfaces. The gap corrosion happens in solutions with gaps or in structural recess. 

TENSION CORROSION - it is a local form of corrosion characterized for the appearance of lashes in material subdue to tension in corrosive environment. Normally it occurs in chloride presence and temperatures above of 60° C.

INTERGRANULAR CORROSION - It is the result of located attack, generally in heating zones of welded parts. Normally it occurs in standard austenitic steel. The risk of intergranular corrosion practically is eliminated when specifying steel with low carbon (0.030%Max.).

An effective cleaning is essential for maintenance of the integrity in the process and corrosion prevention. The choice of a cleaning process and its frequency depend on the nature of the process, the processed food, the formed deposit, hygienic conditions etc.

The indicated methods to clean stainless steel equipment are the following ones: Water and vapor; Mechanical scour; powder and detergents; alkaline solutions; Organic solvents or Nitric Acid washing.

DESINFECTION OF STAINLESS STEEL EQUIPMENTS - Chemical disinfectant are frequently more corrosive than cleaning agents and must be take care in its use.

HIPOCHLORIDES - Hypochlorite and other disinfectant can release chloride, causing pitting. Sodium chloride or potassium chlorides are used in sterilizing agents. If these substances will be used in stainless steel, the treatment duration must be minimum and followed by a quickly rinse with water. In high temperatures, agents contend chlorine should not be used with stainless steel.

QUADRIVALENT AMMONIA SALTS - Much less corrosives than the Hypochlorites.

IODINE COMPOSITES - Can be used as disinfectant of stainless steel.

NITRIC ACID - Even in low concentrations, the nitric acid has a strong germicide action and can be a lower cost disinfectant for stainless steel equipments, especially in pasteurization equipments.

THE TIPICAL APPLICATIONS OF DIFFERENT KINDS OF STAINLESS STEEL:

420 types - Professional and kitchen knifes kitchen house ware, etc.

430 types - Tables, panels and equipment covering; Used in medium corrosive environments. (vegetables, fruits, beverages, dry food, etc).

304 types - Sinks, pipes and machinery parts; (with components that require folding and welding capacity) Better corrosion resistance than the 430 series.

316 types - Components used with more corrosive foods (meat/blood, foods with moderate content of salt), that are clean frequently.

904L types - Used with corrosive foods (hot pickling brine and salty foods).

Duplex 2205 - Used with corrosive foods (hot pickling brine and salty foods); Better resistance than the austenitic.  Good resistance to corrosion under tension in salty solutions with high temperatures.

Super Austenitic with 6% Mo. - Used with corrosive foods (hot pickling brine and salty foods); Good resistance to corrosion under tension in salty solutions with high temperatures. Also used in vapor heating, boilers for water heating, etc.


3. What is the choice criteria of stainless steel for exterior applications, in the architecture?

The stainless steel is selected for application in the architecture, as well as for other applications, for its resistance to corrosion. This is the first consideration in the election process.

Environmental factors as temperature and wetness also need to be considered, but the localization of the project must be considered in first place.

The localizations can be assorted as:

RURAL - non-polluted areas, situated in the interior; far away from industrial atmospheres and residues.

URBAN - residential, commercial areas or with non-aggressive industries polluting the air.

INDUSTRIAL - they are characterized by the pollution of air, through the presence of dioxide of sulfur or gases release by chemical industries, where potentially dangerous condensed acid can be formed.

SEA SHORE - areas with presence of maritime spray or mist. These contain chlorides which can condense when the humidity of the surface evaporates.

The environment cannot be defined precisely as described above, it is also important to consider that climatic changes may occur during the project's life time. In terms, the environment can become polluted or clean in the time being.

Additionally microclimates can influence the general categorizes and must be searched before selecting the type of stainless steel to be used. Microclimates can exist in coastal regions or close to chemical plants, where acid condensed they can be formed unexpectedly.

Generally, the 304 steel can be used in most of the areas, except in highly polluted industrial areas or sea shore areas. In these ones, the prime choice should be the 316.

Other important factors in the steel selection are: Surface finishing, Project, Building technique, Cleaning and manufacture facility, Physical and mechanical proprieties of stainless steel.

- The general rule: The thinner is the covering, better is the corrosion resistance.
- Avoid gaps in the project; they speed the corrosion process.
- Building techniques avoiding gaps must be considered.
- Aluminum rivets must be avoided in the fixation of stainless steel panels, because they can cause galvanic corrosion.
- Periodical cleaning is recommended for the stainless steel, as for most of the materials used in buildings exteriors.
- The mechanical properties of the types most frequently used, 304 and 316, do not demand for concern; however, the thermal expansion of these materials is a third part of the other steel types expansion.
- This differential of tensions between the distended part and the compressed part is responsible for the reduction in the section of the conformed pipe.


4. Which are the main applications of the stainless steel?

Developed originally to applications where the main requirement is the corrosion resistance, the stainless steel also is being wide used for its style appeals and for its hygiene conditions. Here some of the main applications of stainless steel:

Cutlery: applied in the manufacture of places setting, sets of dishes and pans.

Civil construction: used in projects architectural that go since a simple railing or balconies or even the covering of façades, it allows versatility in the decoration. Used wide in sinks and also it is applied in esquadries. Pretty, resistant, easy to install and with low cost of maintenance, stainless steel is the most indicated material in the detailing of projects that search versatility, aesthetic and praticity.

Chemical industry: keeping its properties exactly when it suffers rough changes of temperature or when it is displayed to the corrosion, stainless steel has large used in the chemical industry, either in tanks of storage of products, tubings of circulation of liquids and gases or in other parts and equipment.

Food industry: With easy cleanness, the stainless steel assures better hygienical conditions, what guarantees its wide use in the drinks and foods industries. The quality requirements in consume services also extends the role of stainless steel in snack bars, bars and restaurants. The material not only is seen in pans, sinks and stoves but also gain the walls and balconies.

Furniture: The disinfection procedures used in hospital environments are determinative for the use of stainless steel. However, little by little, the material gains space in the furniture of the Brazilian residences, where it gives refinement and sophistication.

Durable goods of Consumption: the beauty, allied to the resistance, guarantees the presence of stainless steel in products as refrigerators, stoves, machines to wash clothes, wash-wares and electric ovens of microwaves, ovens and other durable goods of consumption.


5. Why to use the stainless steel in washing machines?

The stainless steel is mainly used in the hampers of the modern washers and offers innumerable advantages to its users: beyond the high resistance to the water, soaps, detergents, etc; The stainless steel guarantees the smooth surface and exempts of snaps and barbs in general, preventing the deterioration of fabrics in the process of laudering, caused for irregular surfaces. It also prevents damages that zipperes, currencies, buttons, keys and objects like these, in high speed in the machine, fatally would make in the hampers manufactured with coated materials.
How to keep clean the stainless steel components of the washing machines?
The frequent exposition of the hampers of the washers to water and detergent eliminates any need of cleanness. In the case of something inadvertently to be spilled inside of the units, the nylon sponge or the soft cloth with soap or detergent will be enough for the complete cleanness.


6. Why to use stainless steel in ware washers?

The use of the stainless steel in wash-wares is indicated where it requires beauty and high durability. Beyond the already consecrated use in the internal and external cabinets, other possible applications for Stainless steel include tracks of the hamper and scaffolding of the tracks, deliverering water arms, filters and blades of food removal.


7. Can the stainless steel AISI 416, used in the axle of motobomb, contaminate, in this case, the milk?

The recommended stainless steel for the industry of milk is stainless steel 304, which has a resistance to the superior corrosion to the one of the steel said above (416). In certain parts, as it is the case of bombs, other materials are used; because special mechanical characteristics are demanded.
We understand, anyway, that the contamination, in case that it exists is very small, to the point to be even considered, since milk stays a very little time in contact with the axle of motobomb.


8. Which stainless steel does not produce sparks, for the use in handles of steel and chains of links?

In view of that the stainless steel is conducting of electricity, stainless steel does not exist steel that it takes care of this requirement. In the electrostatic load case, the component of stainless steel will go to produce spark case the dielectric way allows the discharge.


9. I would like to learn more about the most used steel alloys applied in stainless steel sinks.

For production of sinks the 430 and 304 alloys are the most used normally.

The 430 alloy is used when the stamping is not very deep and the 304 when a bigger capacity of stamping is required.

The biggest restriction of steel 430 is his weld ability. The welds in this steel are fragile and of lesser resistance to the corrosion. The applications of the 430 if restrict to that they do not need welding, or when the welds are not considered applications of high responsibility, as it is the case of the sinks of kitchen.


10. I have a small plant of hospital furniture and would like some ideas about how and where to use the material leftovers of plates and tubes.

In case that the leftovers do not have direct application as component of the products that plant, the residual value of the same ones is considerable, what it justifies its sells as scrap iron.
The selling of the scrap iron will be able to help in the reduction of the cost of acquisition of its substance cousin and of its cost of production.
An alternative for the use of the leftovers, could be the production of small parts that could be commercialized as toasts (key rings, door-napkins, door-gizmos, etc). This will depend on the type of generated leftovers and the creativity in the definition of the parts.


11. How should I prepare the stainless steel surface to receive painting, as to guarantee a good tack of the ink? Process for application in high production pieces.

We do not have experience with painting of stainless steel, since in the majority of the applications; the material is used with its superficial finishing gotten by scouring or burnishing.
Given its characteristics of high resistance to the corrosion, one of the advantages to use the steel inox is the fact of this to excuse protective coverings to prevent the corrosion.
In its in case that we understand that the painting thus has aesthetic function and being, the recommendation that we receive from specialists in inks, is to use deep phosphate (Lazzuril or Wanda marks).

We however recommend carrying a test before placing in production.