Re-Galvanizing

[21121956]

Hello everybody:

You may think that this question is silly; but we certainly are facing a dilemma.

As shown in the photograph, tens of hundreds of these bolts, nuts and washers are to fix supports of solar panels. They are galvanized (or were galvanized).

At this time, a Contractor has been requested to carry out the re galvanized.

The Contractor plans to perform a manually cleaning of these elements (just where they are) and then apply the zinc-rich paint.

By the Owner side, it is thought that will be necessary to remove these elements to clean them properly before applying the paint.

Any thought on this? Thanks in advance for your comments.


El que no puede andar, se sienta.

 

[CoryPad]

It is possible to apply zinc-rich paint to in-place fasteners. See section 5.4 here:

ftp://

http://www.mdt.mt.gov/research/LIBRARY/NSBASBCS-2-COATING_SYSTEMS-AASHTO.PDF

 

[21121956]

Hello everybody:

Thank you CoryPad for the info. But, the point is not whether the bolts, nuts and washers can be painted or not “in situ”.

The point is, if to clean them properly (either manually, with electrical wire brush or sandblasting, etc.) is necessary to remove the nuts and washers or not. In other words, disassembling the bolted joint.

We know that the Contractor can remove the bolted joints; this will never be a problem for him/her, but that would take too long time and would cost too much money.

Here is where experience comes into play. What would be expected if these items are not removed and are cleaned only with electrical wire brush (at best) and then painted?


El que no puede andar, se sienta.

 

[SlideRuleEra]

21121956 - Zinc-rich paint is a good product, but it is not equal to hot-dip galvanizing in performance. This is especially true on steel that is not well cleaned (I doubt that in-place fasteners can be properly cleaned).

If the intent of the project is to somewhat extend the life of the fasteners (compared to doing nothing), then the Contractor's proposal may be worth considering.

However, if the project's intent is to protect the installed, existing fasteners so that their projected life is more or less equal to new, replacement hot-dip galvanized fasteners... I would not spend the money on the Contractor's approach.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[CoryPad]

What is your definition of cleaned properly? SlideRuleEra is asking good questions - what are the requirements after coating?

 

[21121956]

Hello everybody:

I favor the second option of SlideRuleEra, because the idea is to have these components in very good condition. Where required, the change will be necessary; I do not know how easy it will be for the contractor to accept that proposal.

I have recently come to this project, which believe it or not, only has four months of operation. Repairs (or changes if necessary) to which I referred should be covered by the warranty.

Once again, thanks for your inputs.


El que no puede andar, se sienta.

 

[dhengr]

21121956:
If I were the contractor, I would buy one third of the needed nuts, bolts and washers new. Then remove the old and install the new ones in one installation operation. The labor and mobilization is going to be a big cost in this operation, so you don’t want to come back to each joint twice. Have the old hardware cleaned by an outfit that has the equipment to do this properly and knows what they are doing, then re-coat them (hot-dip galvanizing) and use those for the second third of the three cycles. At the same time, you use the zinc rich paint to touch up any dings in the rest of the system. Those areas probably can be adequately cleaned with wire brushes, cleaners, etc. If these nuts, bolts and washers have deteriorated after only four months of operation, I would question their original quality and zinc coating, and probably do some testing to confirm their condition. Save the last third of the hardware after re-dipping, and maybe donate those to the owner for their maintenance stores. The original hardware supplier may need this donation to get back in the good graces of the owner.

 

[21121956]

Hello everybody:

Thanks dhengr for your insights. With the ideas that all of you have given me, I think I can propose a solution to this problem.

Opportunely, I will be back to the Forum and tell you about the decision followed and the obtained results.


El que no puede andar, se sienta.

 

[tbuelna]

Galvanized bolts, nuts and washers are cheap to purchase and can be replaced quickly. The man-hours required to clean the fasteners properly, prep them for paint, and then paint them will cost far more.

 

[Doove117]

I agree completely with tbuelna. just replace. I have never tried to clean and put threaded parts back through hot dip. they will need to be spun to get correct thickness on, it's not like hot dipping a beam.
You also mention the plant has only been in service for 4 months so I think your first question is why are bolts and nuts that should last 25 years corroding so quickly...? maybe you should be thinking of stainless or Zylan (PTFE) coated bolts?
To be honest, the bolts in the picture don;t look like they need replacing at all. Except that they're a bit long and most of our clients would make us change them for that reason.
Are you bolting galvanized sheet to galvanized sheet?
If it's stainless then you should have isolation washers between the dissimilar metals.

 

[21121956]

Hello everybody:

Thanks tbuelna and Doove117 for your valuable comments.
They have bolted galvanized sheet to galvanized sheet.

To be honest, the bolts in the picture don;t look like they need replacing at all.

Because of this opinion from Doove117, I am sending another picture.

Once again, thanks.

El que no puede andar, se sienta.