Information on Stainless Steel - Info on Stainless Steel Stainless

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Information on Stainless Steel - Info on Stainless Steel Stainless Powered By Docstoc
					                                      Info on Stainless Steel

Stainless Steel is essentially a low carbon steel to which chromium has been added. It is this
addition of chromium, in amounts greater than 12%, that gives the steel its unique 'stainless',
corrosion resisting properties.

The chromium content of the steel allows the formation of a tough, adherent, invisible, corrosion
resisting chromium oxide film on the steel surface. If damaged mechanically or chemically this
film is self-healing, provided that oxygen, even in very small amounts, is present. The corrosion
resistance, as well as other useful properties of the steel is enhanced by increased chromium
content and the addition of other elements such as molybdenum, nickel and nitrogen.

                            Stainless Steel's healing characteristics

Benefits of Stainless Steel

Long Term Value
When the total life cycle costs are considered, stainless steel is often the least expensive option

Low Maintenance Costs
Stainless Steel normally only requires a periodic wash using a dilute solution of household
detergent and water. Surfaces should be washed with a soft sponge and water.

Ease of Fabrication
Modern steel manipulation techniques mean that stainless steels can be cut, welded, formed and
fabricated as readily as traditional steels and other materials.

Corrosion Resistance
Lower alloy grades resist corrosion in normal atmospheric and potable water environments, while
the more highly alloyed grades can resist corrosion in many acids and alkaline solutions, and
some chloride bearing environments, properties which are widely in process plants.

The mechanical properties of stainless steels allow thinner sections to be used than with other
materials, thus reducing weight without compromising strength. Austenitic grades work harden
with cold working and duplex steels allow for reduced thicknesses over traditional grades.
Substantial cost savings therefore result as well as increased competitiveness with alternative

Internationally recognised as by far the most hygienic surface for the preparation of foods. The
unique surface of stainless steel has no pores or cracks to habour dirt, grime or bacteria. This
cleansability far exceeds other surfaces makes it the first choice for strict hygienic conditions,
such as hospitals, commercial kitchens, abattoirs and other food and beverage processing plants.

Aesthetic Appearance
The bright, easily maintained surface of stainless steel provides an attractive and contemporary
appearance, ideal for a wide and growing range of applications

Technical Info

Sassda offers a comprehensive advice service which covers all aspects of the stainless steel
industry including fabrication, material selection, material and product sourcing, properties,
corrosion resistance, design advice, material identification and failure analysis.

This is supported by a technical reference library containing reports and articles on corrosion
resisting alloys

This service is free to members and their clients provided that the time required to service the
enquiry does not exceed half a day. A charge may be negotiated to cover costs if the the time
required does exceed this.

All technical enquiries are logged and analysed and the results used to determine the content of
technical seminars. These seminars cover different aspects of stainless steel fabrication,
conversion and use and requently incorporate papers by local and internationally acknowledged

To keep abreast of international development and technology, Sassda maintains links with both
national and international technical institutions such as the South African Bureau of Standards
(SABS), Mintek, [The South African Institute of Welding (SAIW)], The Nickel Development
Institute (NiDI) and The International Chromium Development Association (ICDA). It also keeps
in close contact with international [Stainless Steel Development Associations (SSDA's)]

                                      Facts About Stainless

Conditions which favour use of stainless steel

  * Corrosive Environment
  * Very low (cryogenic) temperatures prevent brittleness
  * High temperatures - prevent scale maintain strength
  * High strength vs mass
  * Hygienic conditions required - easy cleanability
  * Aesthetic appearance - no rust, thus no paint necessary
  * No contamination - prevents catalytic reactions
  * Discharge slideability from hoppers
  * Wet abrasion resistance
  * Non-magnetic properties of austenitic grades

Key considerations in working stainless steels

  * KNOW THE MATERIAL - Knowledge improves decision making, avoids problems and saves
  * KNOW THE GRADE OF MATERIAL - Correct material selection is vital - risk taking is costly
  * KNOW THE DESIGN - Good design ensures savings for fabricator and user
  * KNOW SURFACE FINISHES - Good finishes perform well, look good and promote sales
  * APPLY GOOD HOUSEKEEPING - Good housekeeping saves rectification costs
  * APPLY ACCURATE IDENTIFICATION - Lost identity can prove costly
  * APPLY PRODUCTION PLANNING - Planning saves costs and promotes quality
  * APPLY KNOWLEDGE - Remember that additional information if always available through

Other factors

Thermal conductivity
All stainless steels have a much lower conductivity than that of carbon (mild) steel. (Plain
chromium grades +- 1/3 and austenitic grades +- 1/4) This must be borne in mind for any
operation which involves high temperature, e.g. effects during welding (control of heat input)
longer times required for heating to attain a uniform temperature for hot working

Expansion coefficient
Plain chromium grades have an expansion coefficient similar to carbon (mild) steels, but that of
the austenitic grades is +- 1 1/2 times higher. The combination of high expansion and low thermal
conductivity means that precautions must be taken to avoid adverse effects, e.g. during welding
use low heat input, dissipate heat by use of copper backing bars and use adequate jigging. This
factor must also be considered in components, which use a mixture of materials, e.g. a heat
exchanger with a mild steel shell and austenitic grade tubes.

Passive film/passivity
Stainless steels rely on a very thin surface passive film for their corrosion resistance. It is vital to
maintain and preserve the integrity of the passive film.

  * Avoid mechanical damage and contamination
  * Repair any affected areas (e.g. high temperature scale adjacent to a weld, mechanically
     damaged or ground areas), by passivation only or by both pickling & passivation
  * Ensure a constant and sufficient availability of oxygen at the surface of the stainless steel

Stainless Steels have a tendency to gall, pick-up or seize. To avoid this take precautions such as
For surfaces experiencing relative motion minimise the load, ensure no heat build up, keep free of
grit or contaminants, use lubricants or surface coatings

On threaded components the threads must have a high degree of surface finish, components
should have an intermediate to free fit, avoid over torque and contamination of threads.

                                           Surface Finishes

Code for Mill Finish     Description                               Remarks
HRA                      Hot Rolled & annealed                     Industrial heat-resisting and
                                                                   material handling applications,
                                                                   scale impairs corrosion resistance
No 1                     Hot rolled, annealed and descaled         Generally used when smoothness
                                                                   and uniformity of finish are not
2D                       Cold rolled, annealed, and                A uniform, matt finish
2B                       Cold rolled, annealed, descaled           A smooth finish for general
                         and skin passed                           applications
BA                       Bright cold rolled finish. Retained
                         by final annealing in a controlled
                         atmosphere furnace
Mirror Finish
No 4                     Cold rolled, annealed, descaled,          Polished satin finish. Widely used
                         polished to 100grit                       for restaurant equipment, elevators,

                                         Types of Stainless

Austenitic Stainless Steel
These are chromium and nickel containing stainless steels with very low carbon content. They
are non-magnetic, but can become slightly magnetic when cold worked. Cold working also
enhances their strength. Austenitic Stainless Steels have excellent corrosion resistance; good
formability; good weldability, and excellent mechanical properties over a wide range of
temperatures. In addition, these steel are easy to clean, which enhances their use in applications
in hygienic and sterile environments.

Typical application for the various grades include:

Tanks, storage vessels and pipe work for corrosive liquids. Process equipment in the mining,
chemical, cryogenic, food, beverage and pharmaceutical industries. These stainless steels are
also used for manufacturing holloware, cutlery, architectural products and sinks.

These grades have a higher chrome and nickel content that the 304 grade. As a result of their
high oxidation resistance, these steels are used for high temperature applications such as
furnace, kiln and catalytic converter components.

Tanks, pressure vessels, pipe work and components for more aggressive conditions and
specialised applications, such as the manufacture of tank containers for bulk transportation of
chemicals and corrosive liquids. The molydenum content enhances the corrosion resistance.

These are the "stabilised" grades. They are resistant to sensitisation and thus the possibility of
Intergranular Corrosion. In addition they are used in components, which require elevated
temperature strength and corrosion resistance, such as afterburners, super heaters,
compensators and expansion bellows.

Ferritic Stainless Steels

Ferritic Stainless Steel are plain chromium stainless steels, usually with a low carbon content.
They are magnetic and have good ductility and resistance to corrosion and oxidation. They are
generally resistant to stress corrosion cracking. However, there are weldability limitations which
restrict their use to thinner guages. 3CR12 is a special grade, developed and patented by
Columbus Stainless which largely overcome this problem.

Typical applications for the different grades include :

409 - Automotive exhaust tubing and catalytic convertor casings

430 - Kitchen sinks, washtroughs, cutlery, kitchen and catering equipment and utensils.

1.4509 (441) - This grade is specially produced by Columbus Stainless for used in automotive
components. Its superior mechanical strength at elevated temperatures (up to 850 deg C) makes
it the ideal material for the front end (close to the engine) of an exhaust system. It can also be
used for fabrication of heat exchanger tubes.

3CR12 - This is a price competitive, corrosion resisting, weldable, utility ferritic stainless steel with
particular advantages in wet abrasive applications. Unlike other ferritic stainless steels it can be
welded in thicknesses of up to 30mm. It is extremely used in the mining, materials handling and
sugar industries due to its resistance to atmospheric corrosion and wet abrasive corrosion.

                                         Life Cycle Costing

What is Life Cycle Costing?
Life cycle costing (LCC) is a technique developed for identifying and quantifying all costs, initial
and ongoing, associated with a project or installation over a given period. LCC uses the standard
accountancy principle of discounted cash flow, so that total costs incurred during a lifecycle
period are reduced to present day values. This allows a realistic comparison to be made of the
options available. As far as material selection is concerned, LCC enables potential long-term
benefits to be assessed against short-term expediency.

Materials costs are assessed with their implications, for example initial outlay, maintenance and
its frequency, downtime effects, production losses, repair, replacement, and other operationally
related costs such as manpower and energy consumption.

The LCC model is more than a philosophy of forward-thinking. It has been refined to a detailed
system of specific calculations; comprehensive LCC software is available to aid decision makers
to compare accurate forecasts that have taken all the pertinent factors into consideration.

Why Life Cycle Costing?

A full life cycle cost analysis enables the materials specifier to consider the full implications of
future costs, in terms of both actual monetary value, and inconvenience of future maintenance
and replacements. Experience has shown that future maintenance and associated downtime
costs can far outweigh the initial material costs.

The consequences of using the cheapest materials should therefore be quantified before the final
material selection, as it inescapably commits the company/ client to a total financial package.
Generally speaking, the longer the demanded lifetime, the higher will be the operating costs.

Some manufacturers plan for the obsolescence of their products in order to profit from fast
replacement cycles. Reputable companies, on the other hand, understand that the long-term
success of a business depends on being perceived correctly by their markets. Transferring the
benefits of LCC to your customers also adds value to your business. For example, an automobile
that needs to have its exhaust system replaced regularly, will not be perceived as having the
same value of one that lasts much longer.

                      Care, Maintenance and Cleaning of Stainless Steel.

The stain resistance of Stainless Steel stems from an extremely thin but tenacious and self-
repairing film which forms on the surface. This film imparts the properties of Stainless Steel: stain
resistance, non-tainting of food, hygiene, cleanability and the aesthetic appearance that make
stainless steel the ideal choice for many household products. Further, Stainless Steels do not
chip, flake or crack.
Stainless steel will be unaffected by the normal conditions of household ue. Routine gentle
cleansing will reward the owner with a product which retains its properties and appearance
through many years fo constant daily use.

                                      ROUTINE CLEANING

The best method for cleaning Stainless Steel is quite simply soap, or a mild detergent (such as
SUNLIGHT LIQUID®) in warm water, applied with a soft cloth or synthetic sponge. Rinse in hot
water and dry with a soft cloth or allow to 'drip' dry.

Occasionally, the use of a mild household cleaner (HANDY ANDY®) and fine synthetic scourer
(green SCOTCH-BRITE®) or a bruch with nylon bristels may be used.

Routine cleaning applied over several days will generally remove heavy soiling and staining.

Routine gentle cleaning
Household cleaners showing 'suitable for Stainless Steel'
Repeated routine gentle cleaning rather than a single aggressive cleaning

Course abrasive powders
Metallic scourers
Silver or brass cleaners

Remove labels - Remove labels by soaking in a hot soapy solution and rubbing with a cloth or
sponge. If adhesive remains, remove with a soft cloth soaked in alcohol (Methylated Spirits) or an
organic solvent (Benzene). Follow with routing cleaning.

Use a mild household cleaner (Handy Andy®). If heavily stained, pre-soak in hot detergent. Use
a synthetic scourer with fine abrasive cleaners (e.g. Vim®, Ajax®) Repeat if necessary. Follow by
routine cleaning.

Use a thin paste of washing soda (Sodium Carbonate) or fine household cleaners (Handy Andy®,
Vim®, Ajax® made with hot water, on a synthetic scourer. Follow by routine cleaning.

Pre-treat marks with alcohol or organic solvent. Follow by routine cleaning.

Wipe off excess with soft paper towel. Pre-soak in warm detergent. Follow by routine cleaning.

Prolonged soaking in a 25% Vinegar solution will loosen the deposit. Continue cleaning as for
food stains.

CHEMICALS (eg swimming pool acid (hydrochloric), battery acid (sulphuric), tile cleaners
(hydrochloric acid), undiluted bleach.
Rinse immediately with large volumes of water. If staining/damage has occurred contact Sassda.

                                      Typical Applications
    TYPE                                               USE
  301L          Lightweight structural components and panels in transport vehicles.
                Architectural framework and panelling
  304/304L      Cookware, sinks, cutlery, catering equipment, hospital equipment, food &
                beverage equipment, abattoir equipment, pharmaceutical equipment,
                cryogenic, pipework, tanks and process vessels for a large variety of corrosive
  309/309S      High temperature oxidation (scaling) resistance, good high temperature
  310/310S      strength. Furnace parts, muffles, radiant tubes
  316/316L      Pipeworks, tanks, process vessels for more aggressive corrosive liquids and
  317L          conditions in chemical, petrochemical, pulp and paper, pollution control, hydro
                metallurgical and petroleum industries.
  316Ti         Components requiring good elevated temperture strength e.g. super heaters,
  321           compensators, expansion bellows. Equipment exposed to elevated
                temperature/aqueous corrosion cycles. (316Ti for more aggressive corrosive
  409           Automotive exhaust pipes, silencers and catalytic convertors
  441           Catalytic convertors for more arduous conditions than 409. Heat exchangers,
                tubes, geysers
  430           Sinks, washtroughs, trim for domestic equipment, kitchen and cafeteria
                utensils, cutlery.
  3CR12         Ore cars, freight cars, bus chassis, bus frames, chutes, launders, buntons,
                conveyor equipment and systems, tanks. General material handling equipment
                particularly wet sliding abrasion conditions. Structural applications in corrosive
                industries, ladders, walkways, cable racks


3CR12 was developed in the 1970's by Columbus Stainless. It is now recognised as the world's
most specified 12% chromium utility stainless steel.

It is price competitive, corrosion resistant, weldable, utility chromium steel with particular
advantages in wet abrasive applications. Unlike other ferritics it can be welded in thicknesses of
up to 30mm.

3CR12 meets the European standard 1.4003, included in spec EN 10088. It also conforms to
ASTM A240-UNS-S41003.

3CR12 was developed to provide a superior alternative to coated carbon steels and other
materials which have poor corrosive resistance. It reduces costs through eliminating protective
treatments and material corrosion allowances.

It is used extensively in the mining, materials handling and sugar industries due to its resistance
to atmospheric corrosion and wet abrasive corrosion.