Atmospheric Coatings

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The Atmospheric Coatings Technical Community of Interest is a group of people (both AMPP members and nonmembers) who have come together for the purpose of furthering a common cause by sharing wisdom, knowledge, information, and/or data for coatings utilized in environments exposed to the atmosphere.
  • 1.  Degree of required cleanliness for touchup paint application on Hot-dipped Galvanized Structure

    Posted 02-16-2023 10:11 AM

    Dear Experts;

    The subject of query is related to "surface cleanliness on small damages prior to touchup paint application" on base plate of hot dipped galvanized structural members which were fully coated with surface tolerant epoxy mastic paint. 

    Paint damages found at base plate of several structural columns, the damages occurred due to washer plates (06nos.) welded on a base plate of hot dipped galvanized column, the reason galvanization layer is fully removed and substrate is visible from base plate, damages are adjacent to weld beads of washer plates including the extended heat-affected zone (HAZ) area which is approximately 25mm at all around the weld beads, See the below image PIC-2 for reference. The affected area is calculated by considering the maximum length and width of damage at base plate of a column which is less than 0.1m², See below calculation. 

    CALCULATION: (By choosing maximum length and width of damage)

    Area affected due to welding in surrounding of one bolt is 130*30*4 sides= 15600 mm²,                                                                                                                Area affected due to welding in surrounding of six bolts is 15600*6nos.=93600mm²=0.093m²,                                                                                                      Affected area is 0.093m² which is less than 0.1m².

     PREPARED THE SURFACE AROUND WASHER PLATES AT ONE COLUMN: The surfaces were prepared according to project requirements by using combination of tools represented in SSPC-SP2-hand tool and SSPC-SP3-Power tool, rusts and other contamination were fully removed as shown in PIC-1 that may detrimental to a coating system. Our company is proposing to give assurance of life span of applied coating by carrying out Peel-off adhesion test over cured coating with reference to ASTM D3359 type 'A'.

    But our client is not accepting the proposed methodology of surface cleanliness for applying touchup paint application by recommended paint that is surface tolerant epoxy mastic coating.

    In other hand, client is asking to check anchor profile on substrates those prepared in accordance to SSPC-SP2 & SP3 which is not included in our best practice. NEED EXPERT SUGGESTION.

    Are these surface preparation methods (SP2/SP3) are acceptable for small damages on hot dipped galvanized surface or need sweep blast.?

    Adeel Ahmad
    M/s. Tecnicas Reunidas Saudia
    Jazan Refinery and Terminal Project
    Kingdom of Saudi Arabia,
    Phone# +966554863154

  • 2.  RE: Degree of required cleanliness for touchup paint application on Hot-dipped Galvanized Structure

    Posted 03-30-2023 10:22 AM

    Dear Adeel Ahmad

    For touch up in HDG, yoy need Zinc rich epoxy level I (% Zind dust > 85%), according SSPC - PAINT 20. 

    The ASTM A780 Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products,  

    indicates that HDG can be repaired with organic zinc.  Previously I recommend washing the surface with solvents (SSPC-SP1) and later preparing the surface to SSPC - SP11 grade. After that, apply a layer of 3 to 4 mils of organic zinc.
    The thicknesses can be evaluated with ASTM D7091 and the number of measurements is defined in SSPC - PA2

    Best Regards

    Pedro Moreno J.

    Pedro Moreno Junco

  • 3.  RE: Degree of required cleanliness for touchup paint application on Hot-dipped Galvanized Structure

    Posted 04-21-2023 02:03 AM

    Dear Adeel Ahmad,
    Small damages SP2/SP3 surface preparation method is acceptable, especially application of surface tolerant epoxy. which can be applied Power/Hand tool prepared surfaces.
    If you are going to apply Zinc rich epoxy the blasting is the best & only option.
    If you need any more clarification, I am available. thanks

    Vighnesh Kuruppath