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 most of our range of doors and frames for meter box repair and the R16 meter box itself.
Here is some information on the grades of stainless steel we use and performance data that we’ve compiled from the materials science literature and the web.
Grades of Stainless Steel
At Ritherdon we offer 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 on this post). *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.
Corrosion resistant material
The grade of stainless steel is chosen based on the environment that the stainless steel enclosure will be exposed to. Harsher environments will require a higher grade of steel such as 316 grade, which is a marine grade.
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. For further reading on this see ‘corrosion mechanisms in stainless steel’ from the British Stainless Steel Association.
Predicted service life of stainless steel
The 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.
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 maintained appearance for our pillars and cabinets. A long term study at Kure Beach, California (a warm, marine environment) showed no measurable 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.
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.
