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structural integrity of corroded steel structures?

  • 1.  structural integrity of corroded steel structures?

    Posted 16 days ago
    Hi,
    How do we assess the structural integrity of corroded steel structures?

    What methods would recommend to rectify the structural integrity of corroded steel structures?

     

    Thanks,

     

    Damian Carroll

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    Damian Carroll
    Thredbo
    Australia
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    Pro Cert 2


  • 2.  RE: structural integrity of corroded steel structures?

    Posted 15 days ago

    If the structures in the field the only viable initial step is a visual assessment.

    If they seem to be a worry, visable corrosion or bubbling under the protective coating you are in the teritory of having a structural engineer out to look at it and assess looking for metal loss in the welded or bolted connections.

    If repairs are required they need to be designed and scoped (with reference to the anticipated structural loads) and carried out correctly as once you have corrsion going it something you have to consider about where you can connect to the parent material or build it up with reasonable strength with the repairs.

    Finally once the repairs are complete you need to ensure that a decent systems of corrosion protection is installed.

    My experience come from water industry (I am not sure of your context) often we had to just replace structural elements as it was easier than repairs that is with 20% metal loss.


    Regards,

    Ian



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    Ian Lee
    Reliability/Maintenance Engineer
    Nowra
    Australia
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    Pro Cert 2


  • 3.  RE: structural integrity of corroded steel structures?

    Posted 10 days ago
    ​Be careful about terminology.  If you want a "Structural Integrity assessment" then you need a structural engineer and they will need to know the load conditions, the member and connection details, and the corrosion location, type and section loss.  They will probably need to undertaken analysis.   This is a Level 3 assessment of a steel structure.  It is expensive and often unnecessary.  If you have a portfolio of similar assets (e.g. ventshafts, light poles, etc) then you can do a generic analysis and define failure criteria for less qualified field assessment.

    Ideally you follow the IPWEA Condition and Risk Assessment process.

    Level 1 - Cursory visual check - normal operational staff     Outcome  is  Good / Maybe / Bad   assessment

    Level 2 - Systematic visual / tactile inspection of coating, corrosion and estimate of section loss - we would use a civil, structural or maybe mechanical engineer  who can understand the load conditions, critical members and sections, and the deterioration processes.  Outcome is a condition and risk assessment which considers structural issues and risks, failure mode and consequence, deterioration processes and rates, residual service life, and potential interventions to manage deterioration or failure consequence.  A formal structural integrity assessment may be an appropriate intervention.

    Level 3 -  Degree of inspection, testing and analysis depends on the type of structural members and the access available to measure.  Coating and corrosion product removal may be required. Experienced eye, calipers, laser scan, ultrasonic or pulsed eddy current thickness for section loss.




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    Andrew Hackett CPEng NER RPEQ
    Principal Civil Engineer
    Kellogg Brown and Root
    Sydney, Australia
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    Pro Cert 2


  • 4.  RE: structural integrity of corroded steel structures?

    Posted 14 days ago
    Hi Damian,

    We inspect our lighting and service poles by having the wall thickness checked by ultrasound, If the residue material falls below 50% then we have it pulled down immediately for safety as we did have a case of a 25 mtr sports lighting pole fall over due to unknown corrosion below the grounds surface.

    Our contractor also provides us with their recommendation on reinspection timeframes from removal or maintenance required asap up to 5 years all depends on their individual findings, we then created a specific reinspection schedule using their recommendations.

    Happy to email you a couple of past audits if you like to see what they do in more detail if you like?

    Cheers

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    Graeme Clarke
    Asset Inspector
    City of Kalamunda
    Perth WA
    M 0457520140
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    Pro Cert 2


  • 5.  RE: structural integrity of corroded steel structures?

    Posted 10 days ago
    Hi Damian,

    I generally follow Ian Lee's procedure (reply) for our structures. You need to pay particular attention to the connections as, in my experience, you can get a lot of corrosion in these elements as they are normally located in corners where you catch water and have stress concentrations as well. They also have more complex smaller elements joined together and it doesn't take much for the elements to lose significant percentages of cross-sectional area. My understanding also is that most structural failures occur at connections.

    As an example, a corroded staircase job I did in 2018 required this remediation from the Structural Engineer. I closed the stairs and they remained closed until complete renewal. Note this is a specific case and example only. You should obtain your own expert advice specific to your issue. The cost to do remediation (as outlined below) was excessive (very labour intensive) and it was decided to completely renew the stairs.

    Remediation as outlined by Structural Engineer:

    1. Use a mechanical wire brush to remove any corroded areas back to clean steel.
    2. If loss of cross sectional area in each plate element is less than 10% the contractor
    may proceed with this remediation procedure. Otherwise, the engineer shall be
    notified to assess and provide further details. This may involve the addition of new
    plate elements or replacement of sections of steelwork.
    3. Apply cold galvanizing paint or an approved epoxy coating system such as 3 coats
    of Dulux Durebild STE with a top coat of Weathermax HBR. The contractor must
    provide details of the manufacturer's warranty including inspection and
    recommended re-application periods. A re-application period of less than 10 years
    would not be acceptable.

    Advanced corrosion (greater than 10%) shall be dealt with by replacement of the steel
    elements

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    Matthew Holt
    Construction & Maintenance Engineer
    Northern Beaches Council (NSW)
    t 02 9942 2843 m 0466 926 193

    northernbeaches.nsw.gov.au
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    Pro Cert 2