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Impossible to make Zn-Mg-Al ternary hot-dip galvanized steel pipe?

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(-----) December 31, 2021

Q. Zn-Mg-Al ternary steel sheets are being manufactured, but why is Zn-Mg-Al ternary hot-dip galvanized steel pipes not manufactured and must be manufactured from ternary steel sheets?

- Gunsan South Korea

January 2022

A. Hi Lee. I'm sure it's not impossible, and I would guess that it's not even extraordinarily difficult. It's probably more a question of supply & demand. If someone is going to invest in setting up an alternative to conventional zinc galvanizing, galvalume, and the other hot-dipping variations, they're probably more likely to offer continuous coil sheet, with it's 101 applications than pipe with it's very specific diameters and weights. If it's not available today it may be available tomorrow though :-)

Please introduce yourself and your own situation.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

January 5, 2022

Q. Thank you for your attention. My company manufactures hot-dip galvanized steel pipe. This time, we are conducting a high corrosion resistance improvement steel pipe test. It is possible to take a zinc-aluminum-magnesium ternary steel sheet and produce it as a steel pipe. What I am curious about is that no matter how much I search, there is no company that produces hot-dip galvanized steel pipe by forming a ternary system in a kettle. Why?

In the case of a Japanese company, two kettles are prepared, 100% zinc in the first kettle, aluminum and magnesium in the second kettle, and then double immersion to produce highly corrosion-resistant steel pipes. We also made a small kettle to create a ternary system, and tested the steel plate and steel pipe immersion test, but the steel plate is easily plated, but the quality of the steel pipe is not uniform and there is a lot of non-plating. Various conditions such as immersion time and temperature were changed, but the result was the same. Finally, like a Japanese company, we immersed in a 100% zinc kettle once and immersed in an aluminum magnesium kettle a second time, and the plating quality was good.
I don't know the details, but there must be some reason why a Japanese company is producing high corrosion-resistant steel pipes while spending more time using two kettles, but no matter how much I search for data, I can't find it. Thank you.

LEE KYUNG KEN [returning]
steel pipe company employee - Gunsan, South Korea

February 12, 2022

A. There is a difficulty in comparing the sheet galvanizing and the pipe galvanizing. That is Magnesium oxidation problem.
1. Product surface coating oxidation problem. Mg is easy oxidation when pipe out of bath. That is why sheet galvanizing uses nitrogen wiping the sheet.
2. Water quenching oxidation problem. Mg is easy oxidation during water quenching process. Sheet galvanizing is easier control than pipe galvanizing due to uniformity.

Of course, there are many other factors that can contribute to coating defects. The problem of magnesium oxidation is the biggest difficulty.

Mike Wang
Integrated supplier of Galvanizing - Shanghai

February 18, 2022

thumbs up sign Thank you for answer. After researching this and that, I think that it is cost-effective to purchase a ternary steel plate and make a steel pipe.

Q. Lastly, I am curious to know that there is a separate liquid flux required for ternary plating. Is this much different from general hot-dip galvanizing flux?

LEE KYUNG KEN [returning]
steel pipe company employee - Gunsan, South Korea

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