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This presentation is the intellectual property of UltraClean Electropolish, Inc. Do not reproduce in part or in whole without prior written authorization of UltraClean Electropolish, Inc. 03-01-06

Optimization of High Purity Product Contact Surfaces on Nickel Alloys via Electropolishing
R. Keith Raney

R. Keith Raney
• Has been active in electropolishing since 1975 when he and his familystarted the first electropolish company in the southern US. • Developed on site electropolishing in the petro-chemical facilities in Texas. • Worked extensively with nuclear industry electropolishing recirculation piping systems and reactor containments. • Developed procedures for electropolishing 20’ stainless steel tubing for semi-conductor industry. • Designed, Installed, and trained several USbased vessel manufactures electropolish systems. • Active member of ASTM BPE since 2001.


Do You Think This Surface is Easier to Clean or…..



Would This Surface Be Better?

Surface Roughness
• The previous two slides both measure 20 Ra. • To achieve this I had the electropolished coupon sanded to and 80 grit (35 Ra) then electropolished to the 20Ra seen. • 20 Ramechanically polished coupon was sanded to a 180 grit. • The purpose is to illustrate that Ra is not as critical to performance as is the microsurface finish!

2B Sheet MetalSheet Metal 10Ra, 10 Ra – 2B 1500X

How About This vs. ….. 1000 X
1000 X

2B – Electropolished 7Ra, 5Ra – 2B Electropolish 1500X


Mechanical Polishing -Sanding

To achieve a specified Ra on productcontact surfaces most fabricated products must receive some form of mechanical sanding, grinding, or polishing.

Mechanical Polishing -Sanding
MILL FINISH - Hot Rolled Annealed 316 Plate Material

Most alloy plate material used in fabrication is purchased in this condition.

120 Ra

Mechanical Polishing – Sanding
SEM 1500X – 180 grit 304 Stainless Steel

25 Ra
All mechanicaloperations impart a finish similar to the surface shown here.

Mechanical Polishing - Sanding

Ra 11.5uin


Mechanical Polishing -Sanding
• Mechanical Polishing/Sanding/Grinding to achieve a specific Ra will cause a damaged layer and/or heat effected zone (Bielby Layer) to be produced.

Mechanical Polishing -Sanding
• This damaged layer will include material smeared overimpurities such as:

• Abrasive material/compounds • Iron or other contamination from handling/forming equipment • Paint, dye, grease, adhesives

• Mechanical finishing operations all cause damage to the material for some depth below the surface. The depth of this damage will vary depending on how aggressively the material was worked.

The Bielby Layer
Mechanical finishing is performed to achieverequired Ra on metal surfaces will result in crystal fractures and other structural changes. These conditions allow the formation of surface corrosion cells. This condition is known as the Bielby layer.

Electropolishing can completely remove this damaged layer which is believed to be the biggest contributure to rouge formation in WFI systems.

J. Wulff illustrates this damage on honed,ground, and electropolished samples of 18-8 CrNi.
On the honed sample a layer of “Austenite and Cold Deformed Ferrite” sits atop of a layer of “Cold Deformed Ferrite” to a depth of 5 µm (.00002”). The ground sample had seven distinct layers of non-austenite material atop the pure stainless. The seven layers top to bottom; 7. Oxide (0-5µm)

6. Deformed Oxide with Grit Inclusions (5-18µm).001”

5. Deformed Austenite (18-22µm) 4. Cold Deformed Ferrite and Deformed Austenite (22-25µm) 3. Cold Deformed Ferrite (25-29µm) 2. Austenite and Cold Deformed Ferrite (29-34µm) = (.00134”) 1. Austenite only



Why Bother?

Why Bother?

Damaged Layer – “Bielby Layer”


180 grit sanded...
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