Coating Inspection

We are facing a situation where the internal surface of a galvanized fire water line (dry conditions) requires repair by painting. Due to project schedule constraints, re-galvanizing is not a feasible option. In this context, I would appreciate your guidance on any industry-acknowledged repair practices suitable for this application.

Does this mean the pipe was not properly inspected at the galvanizer?

What is your role in this process?

Hola Maharajan lo importante es la preparación de superficie para entonces colocar un recubrimiento adecuado.  Mi humilde opinión seria hacer una limpieza manual ( SSPC-SP2 ) para eliminar rastros de pinturas sueltas y descascaradas, luego una limpieza con solventes para eliminar rastros de polvo o contaminantes, para posteriormente colocar un recubrimiento rico en zinc, ya va a depender el acabado de lo enterradas o bajo que condiciones estén estas tuberías.

Ya si lo que buscas es un rendimiento mas prolongado existen muchos recubrimientos los cuales te dan mayor protección.

For the repair of the internal surface of galvanized piping where re-galvanizing is not feasible, industry practice generally allows the use of zinc-rich epoxy primers or organic zinc coatings as an alternative. depending on the project's specification requirements 

Some documentation may help you find best practice for galvanized repair.

Acceptable methods for repairing hot-dip galvanized (HDG) coatings include:

• Zinc-rich paint 
• Zinc-based solder
• Metallizing (thermal spray)

• ASTM A780 – Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings
• ASTM A123 / A153 
• SSPC Paint 20
• SSPC Paint 29 
• SSPC-PS Guide 12.00 

Hi, Maharajan!
Thanks for galvanizing and keeping the infrastructure safe!
Please, read the following information from the American Galvanizers Association and feel free to contact us if you have any further question:

✅ Acceptable Repair Methods (ASTM A780 Standard)

According to ASTM A780, three materials are approved for repairing damaged or uncoated HDG surfaces:

1. Zinc-Rich Paints

   • Most commonly used for internal pipe repairs.
   • Must contain at least 92% metallic zinc in dry film.
   • Easy to apply and suitable for confined spaces.
   • Touch-up materials are required to meet a coating thickness of at least 2.0 mils (50.8 µm) for one application, and the final coating thickness of the repair area is dictated by the material used to do the repair.. [galvanizeit.org]

Other repairing methods that you can consider:

1. Zinc-Based Solders

   • Applied using low melting point zinc alloy rods or powder.
   • Suitable for small localized repairs.

2. Thermal Spray Zinc (Metallizing)

   • Offers high durability and uniform coating.
   • Requires specialized equipment and access.
   • Often used in large-scale or external repairs. 

🧪 Surface Preparation

Before applying any repair material:

• Clean the surface thoroughly to remove rust, oil, or contaminants.
• Sweep blasting is recommended if rust is present, but avoid over-blasting which may damage surrounding HDG coating. 
• Ensure the remaining HDG coating is at least 1 mil (25 μm) thick before roughening.

📏 Size Limitations for Repairs

For newly galvanized materials:

• ASTM A123: Repair area must be ≤ 0.5% of accessible surface or 36 in² per short ton.
• ASTM A153 & A767: ≤ 1% of surface area or 1% per 1 ft length respectively. 

For in-service pipes, these limits do not apply, but aesthetics and coating uniformity should still be considered.

🎨 Appearance Considerations

• Zinc-rich paints may remain shiny while HDG surfaces weather to matte gray. The most important thing is that the bare spots are protected properly.
• For visible areas, consider returning after 6 months to assess visual consistency.
  
  If you are galvanizing to ISO 1461, the same repairing methods apply!
  Let us know if this was helpful!
  Best, 
  E.

I understand that there could be accessibility problems to use the liquid painting especially if the weld joints are located on the elbows.

The first option here would be a deviation; Galvanizing can protect 5-7 cm damaged area by cathodic protection. So use as it is. Also its a dry FW.

Other option is to use CIPP or flow coating, which will be expensive option