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Pickling and Passivating of Welded Carbon Steel Pipes


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


A. I've personally 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 by ed. to spec at TechStreet] gives any specifics on the pickling.

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


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 from corrosion. However I am not sure how long/effective this technique is.

- Kuala Lumpur, Malaysia


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.


Mike O'Mahoney
- Bracknell, Berkshire, UK

Hi Hisham; 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 whereby you could say "this item is passivated, and that one is not"? Thanks.


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

Corten Steel

sidebar2 ---

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 by ed. to spec at TechStreet] is another designation too. Good luck.

Stephen D. Yahn


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 on C.S. MATERIALS?

- 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 -- they certainly don't mean 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.


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Ted Mooney, P.E. RET
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

September 8, 2014

A. I recently 'passivated' carbon steel pipe, its intended use is for a thermal fluid. Fabrication/welding done before chemical cleaning. But firstly had to remove light surface rust by using 10% hydrochloric acid. HCl did a great job and removed other surface contaminants. Use of HCl is not for the faint hearted! I then applied a 1% sodium nitrite solution with a high pressure spray. Finish appearance was a dull grey color. It's important to note that rust will reappear quickly if left unprotected.

Paul O'Dwyer
- Cork, Ireland

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