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by Ron Joseph
February, 2009
Zinc Metal Spraying
Q. We have a requirement from a large company to zinc metal spray and then paint with 2 part epoxy our zintec 2 metre cubicles 2 mm thick. The application is for a oil rig in the North Sea in the UK. The cubicle type is our standard 2 metre design 2 metres tall and 60 cm wide square, 2 mm thick.
We have had quotes back but this is very expensive £720 each a cubicle and they have also stated we would need to increase thickness of the metal to 3mm and increase hole sizes. Firstly is this necessary are we going overboard with the corrosion protection do we need to change the thickness?. Is there a cheaper alternative that we offer the same type of protection at a more sensible price.
Any advice would be greatly appreciated
A. It appears that the specification your customer sent is intended for hot rolled steel and not cold rolled steel. You are correct in saying that the thin steel sheet metal panels will be deformed.
The Steel Structures Painting Council (SSPC) provides specifications for your application. Unfortunately, I don’t have a copy with me, but you can purchase the manual from the SSPC web site.
If this were my project, I would probably purchase hot dip galvanized steel and if at all possible avoid having to weld the metal, since that will destroy the galvanizing. After fabrication of the panels apply a zinc phosphate pretreatment. If you don’t have the capabilities to perform this in house (bear in mind, this is not a paint), then search for a job shop (custom coating shop) in your local area who has these capabilities. In the US the specification for the zinc phosphate process is TT-C-490 Type I. You can purchase a copy of the spec online. However, I'm confident there is a companion BS specification for this process and job shops who perform the process will know exactly what I’m referring to.
Soon after applying the zinc phosphate apply one or two coats of a high build epoxy primer followed by two coats of polyurethane. PLEASE insure that all the edges, sharp points, edges around cut holes, etc. are adequately protected. Once the panels are exposed to the marine atmosphere it is the edges that will corrode first, and then the corrosion will work its way under the painting film, creeping inwards. Therefore edge protection is critical.
Perform excellent QC to insure that your film thickness is adequate in all areas. Remember, corrosion will commence at the weak areas and then progress.
I don't know who supplies marine paints in the UK, but in the US, Carboline and PPG Ameron cater to the off-shore drilling industry. Research the paint companies in the UK who sell to the marine industry (ships, barges, off-shore drilling, etc.) They will carry the paints you require.
Regards,
Ron Joseph
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