Properties of stainless steel

Most of the enclosure products we manufacture for outdoor use are fabricated from stainless steel.  These include the feeder pillars and service cabinets, but also the range of doors and frames for meter box repair and the R16 meter box itself.  Here is some information on the grades of stainless we use and performance data that we've compiled from the materials science literature and the web.

Choice of materials

At Ritherdons there is normally a choice of three grades of stainless steel, depending on the application for the enclosure:

Grade	Alternative Names	Class of Stainless
4003	Utility grade, 3Cr12	Ferritic
304	1.4301	Austenitic
316	1.4401	Austenitic

Applications	4003 powder coated*	304 powder coated	304 natural	316 powder coated	316 natural
Typical urban and rural environments	X	X	X	X	X
More corrosive, marine or certain industrial environments		X		X	X

The 'natural' finish is a bare metal, but not polished finished (e.g. the photo of the ER150 on the feeder pillar page).

*If left unpainted, the surface of 4003 stainless can become discoloured in certain environments (though it's easily cleaned off, if it does occur), so we only supply 4003 enclosures with a powder coated finish.

Predicted service life of stainless steel

These data on corrosion rates suggest that our stainless steel pillars should last several thousand years!  It's not quite that good...

Corrosion Rate  µm/year

	*304	*316	+zinc	*mild steel
Rural	0.0025	0.0025	0.2-3.0	*5.8
Marine	0.0076	0.0076	0.5-8.0	*34-!178
Marine  industrial	0.0076	0.0051		*46
Urban			2.0-1

*from Action Stainless webpages

⁺from Principles of Corrosion Engineering and Corrosion Control.  Z. Ahmad

^!from Farro et al Mild Steel Marine Corrosion

However, while the figures in the table are reasonable for zinc, which corrodes relatively evenly over its surface, stainless steel corrosion occurs in a very localised way, in microscopic pits, if corrosive ions are allowed to accumulate.  These are some predicted figures (extrapolated from experimental results) for pit penetration times from the British Stainless Steel Association website.

Estimated time (years) to penetrate 1 mm by steel type

	304	316
Rural	770	1200
Semi-industrial	135	525
Marine	145	260

These figures still suggest that our 2 mm stainless steel electrical enclosures will have service lives measured in centuries, rather than a decade or two.

More experimental evidence

Experimental results from long term trials at a marine research station in the Unites States indicate equally long lives and maintened appearance for our pillars and cabinets.

A long term study at Kure Beach, California (a warm, marine environment) showed no measureable pitting (<0.01 mm) of unpainted 304 and 316 stainless steel after 15 years. (Baker and Lee, 1988, Degradation of Metals in the Atmosphere)

Just like grades 304 and 316, the corrosion rates for 4003 stainless are also orders of magnitude lower than those for zinc and mild steel.

Ritherdon & Co stainless steel enclosure design

Because, when it does occur, stainless steel corrosion takes place in microscopic traps for ions such as chloride (often termed 'crevice corrosion'), our pillars and service cabinets are designed with simple, flat surfaces and minimal crevices to encourage rain washing which removes these harmful ions.

Do you have more information on the environmental performance of stainless steels?

If you know of any more sources of information on stainless steel, particularly on environmental corrosion rates for 4003 or 3Cr12, please let us know as we would like to maintain this page as a useful technical summary of stainless steel's performance.