Metal finishing Q&As since 1989

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I WANT TO REMOVE RUST CONTAMINATION FROM 347-H SS PIPE IN THE FIELD

I HAVE 6 INCH 347 H SS TUBES THAT HAVE BEEN DENTED AND SCRATCHED DURING SHIPMENT. THE END USER WANTS TO PASSIVATE THEM TO REMOVE CONTAMINATION.HOW CAN THIS BE DONE QUICKLY AND SAFELY IN THE FIELD. OBVIOUSLY, THE DENTS WILL BE CUT OUT AND THAT SECTION OF PIPE DISCARDED.NEXT , I FOUND A FABRICATION PLANT REMOVING STAINLESS STEEL WELDS ON THE SAME PIPE USING CARBON ARC. CAN THIS BE SAFELY DONE IF THE WELD AREA IS GROUND BACK A SUFFICIENT DISTANCE TO INSURE REMOVAL OF ANY CONTAMINATION ?

BOB L. HELM
- BIXBY, Oklahoma
2006

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Grinding 2 mm off the carbon-arc surface will remove any carbon pick-up that might have occurred. There are no other contaminants resulting from carbon-arc washing, only carbon diffusion into the surface layer.

P.S. Posts are easier to read if they are in lower case typeface, rather than being shouted in all upper case :-)

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2006

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This work can safely be done in the field. I do it all the time. I suggest a two-step process. First, remove the rust. Second, passivate the metal.

I strongly encourage you to avoid using even stainless steel wire brushes or even flapper wheels. Even if they are brand new stainless brushes, they can become contaminated with use. My bigger concern is smearing the contamination into the metal. I address it with a thickened Phosphoric acid blend to dissolve the rust. It isn't as quick as a Nitric/HF style.... but worlds safer.

For stubborn rust, use some Scotchbrite or similar non-woven, non-metallic abrasive material.

When you have ALL the rust removed, passivate the metal with a citric acid blend.

By avoiding the Nitric/HF blends, you should not pull out any chromium, nickel or other heavy metals. The approach listed above addresses iron only... just what you need with rust removal and passivation.

Todd Turner
- Monroe, Louisiana
2006

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Bob,
citric acid passivation solutions are safe and easy to use in the field. Let us know if we can help you.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2006

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2006

Option-1: As the Stainless Steel-347 material is supplied to a Client, the Client will prefer a NEW material. So, it is better to scrap the dented and scratched material and supply all new material.
Option-2: If the Client agrees for a repair on the dented and scratched material, the following procedure may be followed:
Any cold work on removing the stainless steel dent will increase hardness and residual stress in that area. If possible, the dented area/portion may be scrapped.
Pickling and Passivation:
(a). Remove the scratches, projecting marks by grinding. Buff the area with stainless steel wheel buff or stainless steel brush and remove the stain as much as possible.
(b). Passivation: Apply 20 to 50% concentrated nitric acid at temperature around 40 deg C on the rusted/stained surface and soak for about one hour. Water wash.
(c). If trial test shows, the passivation is not removing the rust scales and stains, it is better to follow the Pickling procedure, before passivation:
Pickling:
(c1): If scales are heavy, apply 8 to 10% sulfuric acid at 60 to 80 deg C for about 5 to 45 minutes and clean the surface with water.
(c2). Apply mixture of 15 to 25% nitric acid and 1 to 5% hydrofluoric acid at 30 to 50 deg C for about 5 to 30 minutes. Wash with water and dry the area.
(c3). Ready mixed pastes for Pickling and passivation are also available from some companies.
Note: People in Chemical, nuclear and aerospace industries(piping and equipment in the field), follow the above procedure. As the acids, used for the above procedure are highly corrosive and dangerous, use sufficient safety and Personnel Protection Equipment

Annamalai
- Chennai, India