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Pickling and Passivating of Welded Carbon Steel Pipes

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Q. Hi everyone,
I am a student from the Metals and Materials dept. at UBC, Vancouver, Canada. I'm looking for information on the pickling and passivating of welded carbon steel pipes. I've been searching for this info in the libraries and on the net and the only thing that I'm able to find is on stainless steel. Would anyone have any suggestion on this issue or where I can look up this info (I've checked the ASTM standard and the standard is also on stainless steel).

Thank you very much for the help :)

Winky Lai
University of British Columbia


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A. I've never heard of passivating carbon steel, Winky. It seems like there would be a lot less call for zinc plating, galvanizing, phosphatizing, painting and powder coating if such a thing could be done; I don't think it can. You might look up Corten® steel though, or see if ASTM A569 [link is to spec at TechStreet] gives any specifics on the pickling.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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A. I have some experience for carbon steel passivation using sodium nitrate solution. This will create a thin film of oxide which can prevent the carbon steel form corrosion. However I am not sure how long/effective this technique is.

Hisham
- Kuala Lumpur, Malaysia


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A. Pickling and passivation of carbon steel is relatively uncommon when compared to stainless steel, however I have been involved with large scale pickling and passivation of carbon steel piping for installation at a plant in Mozambique. The pickling and passivation was carried out in Durban (South Africa) and I was in charge of the entire project. The finished product was then shipped up to Maputo by road.

Regards,

Mike O'Mahoney
- Bracknell, Berkshire, UK


Hi, Mike. We understand what pickling is (the removal of scale), why it is done, and how it is done. But I am not understanding what you mean by passivation of mild steel, i.e., what it is, why it is done, or how it is done. What property is claimed for passivated mild steel? Thanks.

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Corten Steel

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A. "CORTEN" is a trade name for this alloy of steel. US Steel owns this name. This is known as a HSLA steel. Which means hi strength low alloy. It has only .09% carbon (low alloy).

Tensile is 70,000 psi. Mild steel is only 60,000 psi. Contact US Steel for full details. ASTM A242 [link is to spec at TechStreet] is another designation too. Good luck.

Stephen D. Yahn



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Q. Have any experience using CORTEN steel for ship funnel main engine exhaust pipe? Does it really prevent rust? How will it look (external) after say 2 months of operations? Exhaust temperature expected approximately 500 °C. External factors - Tropical climate.

Chan YK
- Singapore



October 20, 2009

Q. I want pickling and passivation details & definition. Is it possible to do C.S. MATERIALS?

B.Sudharsanan
- CHENNAI, India


October 21, 2009

A. Hi, B. A problem here is that passivation doesn't have an exact meaning. The most common meaning applies to stainless steel, where nitric acid or alternatives serve to chromium enrich the surface and form a chrome oxide skin. So, when people talk about passivation of carbon steel, what exactly do they mean -- certainly not chromium enrichment.

Some people call chromate conversion coating of zinc plating 'passivation', and others call phosphatizing of steel 'passivation'. Phosphatizing or a similar treatment does offers some degree of rust prevention.

Can you provide context? Texts such as the Electroplating Engineering Handbook provide fairly detailed information about pickling and passivation. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

December 16, 2013

A. Pickling & passivation is a term specified for the stainless steel and this means the removal of the corrupted protective layer of chromium oxide and regeneration of the new protective layer of the chromium oxide and pickling being done by treating the surface by a mixture of HNO3 and HF with different % depending on the stainless steel grade (304, 316, 316L, 316H, 316Ti, duplex, etc.) and passivation is done spontaneously by oxygen in air and can be accelerated up by using an oxidizing agent like HNO3 (10%).

But carbon steel is different and is called chemical cleaning, and this is the removal of the scales and foulants, and passivation is to stabilize the free iron remaining after pickling phase to convert it to magnetite -- and this is done by oxidizing like sodium nitrite at pH 9.5 (use ammonia to raise the pH) or hydrogen peroxide.

Nabil Abdel Malak
- Doha, qatar

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