Spangled and Black Spots on Galvanizing Surface

[patrickhengky]

Dear all, good day everyone. I am facing issues here. I experienced spangled and black spots on galvanizing surface which puzzled me. Is this consider defect and please advise any methods to remove the spots. What is the cause of the problems by the way? Thank you for your help in advance

By the way, the pipes shown had gone through hot dipped galvanized

 

[Daz1968]

When we have black marks in galvanising at work it is usually down to bad prep before galvanising and the surface wasn't fully clean before dipping. Don't think you can clean it up, maybe a coat of galvanised spray may tidy it up ok.