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Stainless Steel

GRADES OF STAINLESS STEEL:

Two of the most commonly used grades of Stainless Steel are Grade 304 and Grade 316 GRADE 304 has good corrosion resistance and is most commonly used for in-door applications. GRADE 316 has a higher level of corrosion resistance. The Grade 316 is often referred to as "marine grade" and typical applications include boat fittings and architectural components in exposed coastal locations and other salt water environments.
Note: Neither grade offers corrosion resistance if submerged in salt water.

STAINLESS STEEL MAINTENANCE:

It is an often held belief that stainless steel is “stain free” and “maintenance free”. This however is not necessarily correct and all grades will require periodic cleaning. Stainless steel does suffer from localised corrosion and discolouration called Tea staining. Tea staining is a cosmetic problem and will not create structural problems with the stainless steel.
The visual performance of outdoor stainless steel depends on five interrelated factors:
• Surface finish - smooth and clean and free of crevices. (Difficult on wire ropes)
• Grade selection - appropriate for environment. (Grade 304 or Grade 316)
• Good design - rain washing and uniform draining.
• Maintenance program - regular cleaning.
• End user expectations.
A number of these options relate to the design and selection stage of the stainless steel construction, but the maintenance and customer expectations are post design & construction.

Routine removal of grime

Stainless steel holds its appearance best if it is washed regularly. When washing use soap or detergent or 1% ammonia solution in warm, low chloride water with cloths or soft brushes to avoid scratching the surface. NEVER USE LIQUIDS CONTAINING HYDROCHLORIC ACID.
Smears will be reduced if the surface is dried afterwards. This treatment applies to bare stainless steel but care should be taken with coloured surfaces.
Coloured and very smooth finished surfaces subjected to excessive brushing or rubbing may lose gloss or even become scratched.
Bleaches are not recommended.
Simply wiping with a damp cloth is not adequate as it smears corrosive deposits without removing them.

Table 1 from the ASSDA ‘Tea Staining’ Technical Bulletin provides a guide to the recommended frequency for cleaning exterior stainless steel.

Recommended cleaning intervals for stainless steel wire rope & handrails

* Cleaning involves washing with potable, low chloride water or washing with a neutral detergent followed by rinsing with potable water.

Grease, oily films and other organic contaminationOils and grease may be removed by alkaline formulations or hot water and detergents or, if necessary, by hydrocarbon solvents such as alcohol, acetone or thinners or eucalyptus oil.

In all cases the surface should be rinsed with clean water and preferably dried.
For directionally grit polished finishes, wiping along the polish direction with very hot clean water and a soft, absorbent cloth is a good final step to reduce smears.
Heat from a hair dryer or glue gun may soften adhesive remnants from labels or protective films for removal. DO NOT OVERHEAT THE STAINLESS STEEL MATERIAL AS IT WILL DISCOLOUR. After exposure to UV degradation from sunlight, adhesives may require similar treatment to grease stains or even abrasion, with the probability of a bright or scratched spot.

STAINLESS STEEL CORROSION:

Both 304 and 316 have good to excellent resistance to corrosion. However various factors can occasionally affect their performance.
All grades of stainless steel are susceptible to some form of staining and periodic cleaning is required. The staining is mostly caused by foreign contaminates (see Contact Corrosion). Some of the various forms of corrosion are briefly described below.

PITTING CORROSION: Usually includes moderately high temperatures, high levels of chlorides (ie sea water) and acidic conditions. Pitting, once initiated, tends to grow. The effect can be isolated areas of corrosion or staining.
CREVICE CORROSION: The corrosion resistance of stainless steel is dependant on a protective oxide layer on its surface. Areas where the oxide protection can break down can be where the material is in constant contact with another surface, forming a minute gap where a contaminate, such as sea water, can be trapped and become stagnate. Crevice corrosion is very similar to pitting corrosion but can be much more severe and can also occur at much lower temperatures.
STRESS CORROSION: In certain, often extreme conditions, the combination of tensile stress and corrosive environments can cause a rapid and severe form of corrosion. The likelihood of stress corrosion is not significantly less in G316 than in G304. The most damaging environment is sea water at high temperatures particularly in wet/dry conditions.
GALVANIC CORROSION: The most common cause of any corrosion, stainless steel is also prone to some degree. Galvanic corrosion arises from the contact of two dissimilar metals in an electrically conductive liquid. The best method to avoid galvanic corrosion is to avoid contact with dissimilar metals. The use of an anti corrosive jointing compound is one simple method.
N.B. When fixing stainless steel fittings to aluminium, a jointing compound is highly recommended to prevent galvanic
reaction corroding the aluminium.
CONTACT CORROSION: A combination of pitting and galvanic corrosion, that occurs when small particles of foreign matter, such as carbon steel, are left on the surface of stainless steel. In most cases the foreign matter is eaten away, but in severe cases a pit may also form and pitting corrosion can start. The most common cause of contamination is debris from nearby grinding or from tools contaminated with metal filings.

Stains caused by contact corrosion can be fairly easily cleaned by using Scotchbrite pads or stainless steel cleaner. Do not use steel wool or any polishing or grinding tools contaminated with metal filings.

MECHANICAL PROPERTIES

(In particular reference to Breaking Strengths)
It should be noted that although the ultimate breaking strength of Stainless steel compared to mild steel is relatively high, the yield factor of stainless steel is much lower, ie the yield strength can be as low as 40 – 45% of the ultimate break-load
N.B. It is important to make allowances for the low yield factor when designing structures that require a safe working load. The usual proof tests of half-load can not always be applied to stainless steel products. We advise consultation with your supplier for advice before conducting proof tests. It is not feasible to quote yield strengths as this can vary greatly from item to item and application. Keble’s Trading Pty Ltd will not be held responsible for any replacement of products proof tested without prior consultation.

Disclaimer:

(1) The above information is only given as a guide or general information. If the information given is insufficient, or if you are not satisfied, or certain, we suggest you seek further advice from a professional metallurgist.

(2) For safety, structural and strategic applications, independent engineering or specialist advice should be sought from the relevant authorities/experts. Based on this advice, our sales consultants can assist with the supply of rated fittings for these applications as recommended/nominated by your professional, qualified engineer. Under no circumstances is Keble’s Trading Pty Ltd or its staff authorized or qualified to make any recommendations whatsoever regarding design or selection of fittings for such applications.

(3) Keble's Trading makes no recommendations or claims for the performance and mechanical properties of Stainless Steel and accepts no responsibility or liability whatsoever for any unsatisfactory outcome, unsuitable application or installation of these products.

(4) Keble’s Trading Pty Ltd makes no recommendations and takes no responsibility for the use of any fastening system or products used in the installation of any Balustrading and Handrail components. The responsibility of the design and choice of fastener for compliance to Aust Standard and relevant codes lies soley with the purchaser. Please consult appropriate authorities and or the advice of professional persons for information on correct design and installation techniques.

(5) Product information contained in this website is intended to be used for reference only. Keble’s Trading Pty Ltd strongly recommend that you confirm all relevant details before ordering as information is subject to change without prior notice. If product dimensions are critical to your application, please contact us for assistance.