Marine coating
There is some confusion about what the criteria for Marine coating requires.
A marine environment is determined as Corrosion Class 4 that is between 50m and 2000m from the sea. It can also include some industrial environments and swimming pools.
The problems caused to powder coating in these environments is early failure due to corrosion from chloride ions found in the atmosphere close to the sea.
This corrosion starts at cut edges or defects in the powder coating and is a type of corrosion called filiform corrosion.
There are two mechanisms to avoid filiform corrosion by the powder coater.
- Powder coating thickness, thicker coatings form a more uniform protective layer on the substrate. There is less tendency for small pinholes, or scratches to penetrate the paint layer to the base metal. For Marine coating it is always recommended to have coating thickness of greater than 60um (microns). Akzo our main powder supplier recommends greater than 70um (microns).
- Pre-treatment, Filiform corrosion form around alloy elements that act as seeding sites for the corrosion, the corrosion then travels along grain boundaries in the metal structure. The pre-treatment for Marine requires increasing the grain size at the surface which requires the removal of a layer called the deformation layer that is typically of small grain size, it also requires the removal of excessive alloy elements at the metal surface. This requires etching of greater than 2g to remove the deformation layer, and 0.5g of this is required to be done using an acid etch process to reduce the alloy elements at the surface.
Vertik-al process is operated to Qualicoat sea-side specification that guarantees the correct etching parameters.
Vertik-al are also able to guarantee coating thickness of greater than 60um (microns) for marine applications.
Marine guarantee procedure and rules:
When is job is located in a C4 environment a marine request is made by Vertik-al to the powder supplier.
The customer is asked to complete a marine request form detailing the location, the class of powder and the C4 environment. The powder supplier normally requests the location identified on a map.
Once approved Vertik-al stipulate the following conditions:
- Minimum 60um (microns)
- Continuous coating (all over) except where the item is to be bonded
- All cut edges are sealed, using sealant or paint
- The parts are cleaned regularly and documented, this is at a frequency determined by the guarantee or 12 months.
The Guarantee is for the cured powder by the powder supplier that covers deterioration of gloss or colour for the duration of the guarantee up to the maximum % change specified in Qualicoat.
Most applicators only offer the guarantee on paint gloss and colour.
Vertik-al offer additional guarantee against adhesion and filiform corrosion where the conditions have been met for 25 years except where the powder guarantee is less.