Summary for pit marks on galvanized sheet Discussion
pit marks on galvanized sheet are discussed as a defect that can appear after the strip leaves the zinc bath, but the thread does not give one single universal cause. Vijendra Das asks for the actual reason the defect evolves on GP sheet after the bath. Mike Wang first says a photo is needed for proper analysis. In the related earlier answer, Mark Postema says pitting can form in many ways, but in his experience the number one cause is a buildup of iron fines on the pot turn roll or sink roll; he recommends a scraper, or replacing the roll if needed. He also notes that lowering bath tension may mask the issue, consistent bath temperature helps prevent buildup, and skin passing may help but will not eliminate the problem. The later reply from the editor says a full theory would require a book, not a forum post.
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November 13, 2021
Dear sir ,
I’m working at 25 TPH Galvanizing unit running with 0.6 to 0.12 mm Thickness sheets. My query about pit marks defects are not really solved satisfyingly. So can you please give me a short but actual reason about how this defect evolves over the GP after coming out from the zinc bath?
Vijendra Das
– Dalli Rajhara
A. Better provide a photo of pit marks for analysis.
Mike Wang
Integrated supplier of Galvanizing – Shanghai
February 12, 2022
Ed. note: Photos should be attached to e-mail to finishingdotcompublic@gmail.com for posting here.
⇩ Similar, related, Q&As — oldest first ⇩
Q. Dear sir, I’m working in continuous galvanizing line having capacity of 26TPH, producing sheet of thickness 0.12 to 0.6 mm. Sometimes pit marks are observed in galvanized sheet. What is the reason for pit marks?
Harsh postiwala
Essar – Hazira, Gujarat, India
2006
A. Pit marks can be formed in many ways . If your CRFH Material is good being paid off at your entry section then many of the causes can be eliminated. The number one reason for pitting in my experience is the of a build up of iron fines on the pot turn roll ” sink roll ” . Having a scrapper for this roll helps greatly. Other then that replacing the roll is the only other option. Masking the problem may be done by lowering the tension setpoint at the bath. Keeping a consistent bath temp is key to not allowing buildup to occur. Also skin passing your material may help but not eliminate the problem you’re having .
Mark Postema
– Rancho Cucamonga, California, USA
2006
Q. Hi sir. Sandip, working in steel in India in super galvanizing line. Capacity of line is 0.3 mm to 3 mm thickness and width capacity is 750 mm to 1550 mm.
I want to know about pitting defect on the sheet surface.
Please provide me full theory about this matter. Once again I ask you.
Thank you
sandip singh
– khopoli, Maharashtra,India
September 16, 2014
“Hot Dip Galvanizing of Steel Structures”
by Kuklik & Kudlacek
on Amazon
or
or
(affil link)
A. Hi Sandip. “Full theory” about the defects would require a book .
rather than a forum response, but if you can explain your current situation, and/or try to phrase your question in terms of the excellent response offered by Mark Postema, the readers can hopefully help you move forward towards less pitting. Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
September 2014