Back to all articles

Corrosion- what is it and is it preventable?

Corrosivity

What is corrosivity?

I was in the UK recently visiting family and visited Cromer, a seaside resort in Norfolk. They have a few old tractors which they use to drive into the water to drag boats up the slipway. The main one is a classic old Muir-Hill (yeah I haven’t heard of that brand either) and the rust on it is as thick as anything. Anyway, it got me thinking about corrosivity.

According to the Australian Standard, corrosivity is “a measure of the ability of the environment to cause corrosion. Often used interchangeably with the term ‘corrosion rate’.” In layman terms, how fast it rusts (duh). It’s important because Curtin Uni says corrosion costs Australia up to $32 billion annually or $1,500 per person per year. So that’s a lot. And they also add that most of it is preventable, so that’s good.

 

What does it apply to?

We’re talking from a shade structures and covered areas perspective. The main application is the steelwork, but it also applies to fasteners and fixings, roofing and rainwater products, reinforcing and footing components and ancillary items.

All these products have some corrosion over time, so the goal is to limit this to an acceptable level. This is done with a number of factors in mind, including the corrosivity rate (or risk level), design life of the structure, expected maintenance regime, cost factors and client requirements.

The cost factor is an interesting one, and any astute buyer would realise the benefit of investing a little more upfront for a longer product lifespan. There are two factors to “lifespan” – firstly the Life to First Maintenance, and secondly the Design Life. Both should be considered in any comparison of products.

 

What are the risk levels?

Corrosion is primarily caused by two main factors – salt or industrial pollutants. I’m not going to get too much into the need for oxygen and electrolytes, nor into micro- and macro-climates. (Go read the standard nerd.) But in simple terms, the closer you are to the ocean, especially rough oceans, or to polluting factories (carbon tax anyone?), the higher the risk.

There are a few other common things we come across:

  • Abrasions (someone using a whipper snipper around the bottom of the posts, or kids scratching the paint off)
  • Structures around swimming pools (all that chlorinated water)
  • Poor structure design (nice little pockets that catch water)
  • Poor coating application (1st day apprentice)
  • Poor product specification (i.e. just read this guide and you’ll be OK)
  • Dissimilar metals (stainless steel touching mild steel – a big no-no)

The standard has some complicated maps and guidelines for defining the Corrosivity Category, but this picture shows it better. OK, not so technical, but easier to understand. In essence, nearly no C1 exists in Aus. C2 is common inland (for Sydney, sort of west of Parramatta, and much closer to the coast in Melbourne), C3 for coastal, and C4-C5 for very near the coast.

Now Bluescope has decided to word it differently (to be difficult?), but once again it is based on distance from the pollution source. I don’t know if they’ve had a good look at the corrosion rates in Newcastle, but I think they have a mill there, so I presume someone has.

 

What products can be used?

Right, so down to business. What can I actually use that will last? The below table is quite a generic guide but it should provide some pointers. Best thing to do is give us a call if unsure.

Steelwork Roof sheeting Rainwater products Fasteners
Low risk areas Galvanised, painted or powdercoated Zinc or Colorbond Match roof sheeting specification AS3566 Class 3
High risk areas Galvanised, or a high specification coating system Colorbond Ultra AS3566 Class 4
Severe risk areas Galvanising is a safe option Colorbond Stainless Steel (we provide finance) Stainless steel fasteners

 

 

What about maintenance?

Maintenance is probably the largest overlooked item in the longevity of a structure. In an area with high levels of airborne salt, simply washing the structure with tap water every 6 months can majorly reduce the risk of corrosion. Now there’s some technical stuff in here and Colorbond has some lengthy guides, so give us a ring for more details. The one takeaway: the small cost of regular maintenance is much cheaper than the large cost or re-coating or replacing.

 

What standards and references apply?

This is a non-exhaustive list of standards that apply to the topic:

  • AS2312 (Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings)
  • AS 4312–2008 (Atmospheric corrosivity zones in Australia)
  • AS 3566
  • ISO 9223 (Corrosion of metals and alloys – Corrosivity of atmospheres – Classification)

And these are some sites that provide further reading:

  • Galvanizers Association of Australia
  • Dulux, Interpon and other protective coating suppliers
  • Bluescope

Sources & acknowledgements

  • Dr Reza Javaherdashti – Research Fellow at Curtin University School of Civil and Mechanical Engineering
  • Bluescope – steel grades

Greenline worked to our time line and delivered as per the spec. Their work was what was expected.

MBS PTY LTD - Mark Conroy

Friendly, professional communications and extensive help provided in the grant application process as well as excellent execution of the project.

Barnawartha Primary School - Bernadette Kelly

Extremely easy to deal with. Professional service. Very happy with the completed job.

Echuca East Primary School, Jodi Boal

I find engaging with Greenline completely professional. The customer service is exemplary and the three projects I have been involved in with Greenline gives me confidence in their communication, ability to meet deadlines and appease a customer, quality of work, competency in meeting regulations and OHS measures

I have great confidence in this team/company.

Wodonga Primary School - Damian Duncan - Principal

I have used Greenline for a number of years now as I have always found them to provide excellent customer service, great quality and reliability. Our most recent project was a covered walkway to provide extra shelter for our students.

From day one, the walkway was such a big hit, with so many students using it that we actually had to provide extra staff in the area for additional student supervision. Thank you Greenline.

Wyndham Central College - Bryan Wollard - Assistant Principal

From my first meeting with a Greenline representative I was very impressed with the professional presentation about the company.

The process relating to construction was very well explained with timelines, contractors details and

Overall, the finished product is absolutely great. It has exceeded all our expectations and is now a real asset for the school.

Greenline did a great job here and I would recommend them to any school wanting to develop a COLA.

Ardeer Primary School - Graham Miller - Principal

Greenline were a pleasure to deal with. Their communication was excellent and we are thrilled with the end product.

Mount Waverley Heights Primary School - Sharon Reiss-Stone - Principal

A huge thank you and congratulations to the team at Greenline for delivering BIG TIME our outdoor shade shelter. The shelter, which covers one of our outdoor basketball courts, gives our students a chance to play through all weather conditions and looks great. Their post project support has been fantastic with quick follow-ups and service to the school.

Croydon Hills Primary School - Christian Holdsworth - Principal

We found Greenline to be professional throughout our entire business relationship, from our initial communications through to the completion of our project. Their friendly, helpful advice was offered with constant consideration of our needs. Greenline were able to meet all deadlines with competency, completing our project with the highest quality of work.

Bundoora Primary School - Lee Pollard - Principal

Greenline were a professional and well organised company to work with. The finished product was of a high standard and met the school’s requirements.

Wiley Park Public School - Rene Demos - Principal