Selection of stainless steels for building internal applications

Introduction

Stainless steels are selected for architectural applications, as with most other applications, for their corrosion resistance and potential aesthetic appearance.
These are usually the prime considerations.
For internal applications other factors can also be important, including: - Risk of the fingermarking from contact with 'human traffic' (on wall cladding and lift panels) risk of scratching or staining from contact with glasses or drinks (bar tops) can routine cleaning be expected to maintain the surface appearance but not cause any unacceptable changes in appearance

Selection of stainless steel grade

With the exception of harsh internal environments often encountered in leisure and hydrotherapy pool buildings, grade selection is not a critical factor.
For most building interiors intended for human occupation, either the ferritic 430 (1.4016) or austenitic 304 (1.4301) can be considered.

Depending on surface finish, there can be slight natural colour differences between them, which could influence the choice. The ferritic steel can have a blue tinge, whilst by comparison, the nickel containing 304 has a slight yellow tinge.

Surface finishes

There is a wide range of possible finishes.
Normally 'ex-mill' finishes, with the exception of the bright annealed, 2R finish, may not be considered as aesthetically suitable as textured, polished and coloured finishes.

British Standard BSEN 10088-2:2005 defines these basic 'special' finishes in table 6.
Specifying finishes to BSEN 10088-2

The finishes include:

    Patterned
    Corrugated
    Mechanically Polished or Brushed
    Coloured

 

Mechanically polished or brushed finishes

This includes a wide range of possible finishes, including designations 'G', 'J', 'K' and 'P' of BSEN 10088-2.

Brushed finishes may be better choice than 'ground' or 'polished' for preventing fingermarking.

As the austenitic 304-type stainless steel is not particularly hard, highly polished surfaces can be susceptible to damage. Where surface scratching is very likely on bar or counter tops, then a uniform (non-directional) polish may be better than directional finish.
Unless contaminated with iron from normal carbon steel, however, scratches on stainless steel do not detract from their corrosion resistance in such application areas. This is due to the 'self-healing' nature of the passive surface layer on the steel.

Coloured finishes

Colours including blue, black, bronze, charcoal, gold, green and red are available on 304 (and 316) steel types.
These colours can be applied to mill, patterned, polished, bead blasted or etched surface finishes and offers a wide range of colour and texture. The colour does not contain dyes or pigments, but relies on light interference path difference effects in a chemically thickened surface passive layer.

Generally colouring is done on sheet material before fabrication and so the scope for complex shapes or forms may be limited.
Surface scratches are difficult to repair and so this range of finishes may not be suitable for high traffic areas and is better suited to cladding or roofing applications.

Patterned finishes

Cold rolled embossed, three-dimensional patterns to either one or both sides.
These '2M' finishes help mask scratches and marks and so are useful in high traffic areas, especially lift doors, fascias and lining panels. Sheets with patterned rolled finishes, depending on the pattern depth, can exhibit improvements in stiffness for panel applications.

Corrugated shapes

Cold rolled finish '2W' in trapezoidal or sinusoidal patterns are also specified in BSEN 10088-2.

Fabrication methods and risk of bi-metallic corrosion

Joining methods is generally not an issue in terms of preserving corrosion resistance in indoor locations.
The preservation of pre-prepared finishes is likely to be more important and so 'non-thermal' joining methods are probably the best options. These include:

    mechanical fastening (rivets, screws etc)
    adhesive bonding

 

As the environment is usually dry, bi-metallic (galvanic) corrosion where there is contact with other metals, should not be a risk.

Cleaning and maintenance

Routine cleaning using mild detergents followed by adequate rinsing and drying to avoid drying stains should normally be adequate.

Abrasive cleaning materials may harm some finishes specified for internal applications and should be avoided, where possible.
With directional brushed and polished finishes, align and blend the new 'scratch pattern' with the original finish, checking that the resulting finish is aesthetically acceptable.

Either spray polishes or rubbing with 'baby oil' can be useful in suppressing fingermarking, provided the oil is applied carefully so that it does not allow dirt to adhere to the treated surfaces.

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