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topic 53891

Electropolishing stainless steel tubes


A discussion started in 1998 but continuing through 2018

(1998)

Q. We are polishing small bore stainless tube which has been slotted. Can anyone advise on reasons for some defects we experience:

  1. General pitting defects on the inner and outer surface.
  2. A single deep pit on an otherwise perfect surface.
  3. A rippling effect on the inside of the tube.
  4. An orange peel effect on the outer surface.

Are these more likely to be caused by the raw material or the process parameters?

Thanks

Henry Lupton


(1998)

A. Dear Henry:

Pitting problems are difficult to trace by remote control. The problem can be caused by any step in the operation, including the choice of the metal, the mechanical finishing, the cleaning and descaling, the physical electropolishing setup, and the condition of the electrolyte. We do trouble-shooting of electropolishing problems by a process of elimination, not by speculation.

Ed Bayha
Metal Coating Process Corporation - Charlotte, North Carolina


--

Trouble in Your Tank
by Larry Durney
from Abe Books

or

A. Ed: Yes it is very difficult to troubleshoot a process from a distance, even with the parts sitting right in front of you, let alone from photos of the defects, let alone from a verbal description of the problem and not even a photograph. Still, if we believe in process of elimination, there is a step 1 smiley

Henry: There are some good troubleshooting hints in the electropolishing chapter of The Electroplating Engineering Handbook, edited by Larry Durney. And his book, "Trouble in Your Tank" is the industry's definitive guide to methodical troubleshooting. Good luck.

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


(1999)

A. The problems you describe could be related to the method used to manufacture the tubing, the electropolishing process used, or a combination of the two.

Stuart Spars


(2005)

A. Let me answer your questions one by one.

Please inform, is it a straight tube, welded or seamless. If seamless, has it been cold Drawn / Pilgered?

1. The Pitting is due to high current and the inclusions in the stainless Steel that has created Galvanic Cell.

2. I have to see the sample. Can't answer.

3. It can be if it is a Pilgered Tube where the reduction of OD and wall thickness is of different factor. We call it 'Q' Factor.

4. It seems that the pipe is Seamless as during Direct Extrusion, there is "ORANGE PEEL" surface generated due to use of Glass as lubricant during extrusion. Further, if it was Cold drawn / Pilgered, the reduction percentage was not sufficient to remove the "ORANGE PEEL" surface.

S. H. SHAH
- Ahmedabad, Gujarat State, India



(2004)

RFQ: We require SS-304L/316l Electropolished Inside Seamless Tubes, in various sizes & length, please contact us with details i.e sizes, specifications, etc.

Ashwini K [last name deleted for privacy by Editor]
Mfg - Kolkata, West Bengal, India
^- Sorry, this RFQ is outdated
     View Current RFQs




Can we electropolish without mechanical polishing?

(2005)

Q. We would like to eliminate/reduce the need for mechanical polishing of 304 seamless stainless steel tubing prior to electropolishing.

We are making an assembly which requires SEAMLESS 304 STAINLESS STEEL TUBING 1.0" O.D. X .93" I.D. The tubing sections are approximately 7.799 long. We have been purchasing standard lengths of tubing, and using our laser tube capability, we have been cutting holes and slots into the tube and then laser cutting them to length. After welding 3 other components to this tube section, the assembly must be electropolished. We must manually deburr and polish the assembly before electropolishing due to the dull, hard, extruded finish on the seamless tubing. Even with the time consuming manual polishing the tubing does not always electropolish to our customers requirements.

As others have mentioned in this forum, we would like to proceed with a process of elimination approach this issue. The assembly must electropolish well for the beverage industry.

Any suggestions as to how we must specify and order this tubing? Bright solution annealed possibly?
Thank you.

Michael S. Dersch
- Rockaway, New Jersey



Better process for stainless fork tubes for 3-wheel motorcycles?

December 5, 2009

Q. What material and process of a finish would be more uniform and as good looking, or better looking than the mirror polished finish I am currently using on my 36" long, 2" square, 7 ga., 320 pre-polished 304 stainless steel tubing that we first have machined (a few holes, a slot at one end, and cut to 36" long, with no protruding areas) and then mechanically polished (machine sanded) to 400+ grit and lastly wheel buffed to a mirror #8 finish? Something that will equal the look of a good chrome plating, but that is not hard to get done within a 100 mile radius of Louisville. I am concerned that I might encounter problems with the plating peeling or flaking off later which would be disastrous for us to correct for our customers, as they are located nationwide. Essentially all of our motorcycle is stainless or marine grade aluminum. I would hate to use chrome plated steel, because of the ability for it to rust. Our forks are presently stainless steel. I have thought about continuing to have them mirror-finished and then electropolished, if it is the way to avoid the delicate surface of the polished stainless surface, cosmetically. I welcome and appreciate all suggestions.

tom walters
Tom Walters
product designer and corporate owner - Charlestown, Indiana
outdated


March 2014

A. Hi Tom. Although problems can sometimes be encountered in electropolishing (as in any process), if done right it is the perfect answer. It will smooth the tubing, keep it reflective, and powerfully deter rust.

Regards,

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


December 16, 2009

Q. Dear sir,

I am in India.

I am doing electropolishing of stainless steel tube. but I can't find good result after the electropolishing. Please suggest to me which acid I use for better smoothness and sign.

Jatin Patel
plating shop - Ahmedabad, India


December 16, 2009

A. Hi, Jatin. Please see the Electroplating Engineering Handbook as it has an excellent chapter on electropolishing of stainless steel, including many different acid formulations. But many different acids have been used successfully, so I would guess it more likely that your problem is in low current density, inadequate solution movement, insufficient cleaning, or excess water in the acid than that you managed to discover an unworkable acid formulation :-)

Regards,

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


December 21, 2009

A. Jatin, there are many different types of stainless steels and many different types of electropolishing solutions for them. The basic formulation for stainless steel is a mixture of phosphoric and sulphuric acids; the major solutions are based on sulphuric acid contents of between 15% and 60%, with between 30% and 63% orthophosphoric acid, the remainder is water. The technology is relatively easy, but you do need to know what stainless steel you are treating! There are other solutions available, but they may not be as good as the sulphuric acid/phosphoric acid mixes. By the way, it is very difficult to successfully electropolish 400 series stainless steels.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


December 21, 2009

On Trevor's comments:
Many years ago, I used a proprietary solution on Jetheat which is a modified 410 SS with excellent results. I tried to use the same parameters on a friends 17-4PH and nearly ruined it.

Different solutions work better than others on certain alloys.

See if you can find the series by Charlie Faust in Metal Finishing magazine, probably in the late 80's time frame. He was the accepted expert at that time. It will be a big help, if you can get it.

James Watts
- Navarre, Florida


January 8, 2010

A. The results you say you get: are you talking about the inside of the tube? Usually the inner area of a tube are low-current density sites. depending of the size of the tube you can use auxiliary electrodes, if this is not possible you can use higher current density and stirring.

Hiram Gomez
electrochemistry student - GDL, Jalisco, Mexico.


January 14, 2010

A. I have very successfully demonstrated to a large US Corporation, the electropolishing of the ID of tubing, which is what I presume to be the nature of your enquiry.

I would like to raise a few points which might assist you with your problems. Gassing, seems always something that affects the surface of tubing. To reduce the incidence of this, short lengths can be processed vertically in the tank but should you have long lengths of tubing, then look to pumping the electrolyte through the ID during processing.

Then of course, you have to look at the parameters of your process and examine the current density to determine that your amperage is delivering what is necessary to achieve the results you are seeking

Test the efficacy of your results by looking at the chrome to iron ratio and surface profile after electropolishing.

To offer a more qualified answer we need more information regarding lengths, whether or not you are referring to the ID and the ultimate use of the tubing.

Joel Levinsohn
Joel Levinsohn
- Sydney, Australia


June 10, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My situation: Respected sir kindly suggest me the procedure to electropolish 20 ft x 2 inch dia stainless steel pipe to electropolish from inside.

Hanumant Navale
Buyer - Pune , Maharashtra, India


June 2018

The Electrolytic and Chemical Polishing of Metals
by Tegart

A. Hi Hanumant. As you can see from this thread, successful electropolishing of stainless steel requires a significant knowledge base; and even with that general knowledge base, the electropolishing of the inside diameter of a 20-foot long pipe requires knowledge, experience, and a proper plant.

Please tell us what alloy this pipe is. And can you please very briefly describe the facility you have on hand (length & depth of electropolishing tank, rectifier rating?) and your prior electropolishing experience (biggest pieces you've electropolished, any ID electropolishing experience?), so readers have a good starting point for trying to help you? Thanks!

Regards,

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



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