Jan 7, 2012

Is electropolishing actually necessary given that a 1.0 or greater Cr/Fe ratio can be achieved by passivation alone? The real question is, “Are we trying to only passivate the surface or are we trying to produce a corrosion resistant cleanable surface?” Chemical passivation will attain a chrome to iron ratio above 1.0 (Cr/Fe), without producing any measureable change in the finish characteristics of the surface. Electropolishing is designed to remove surface damage from mechanical polishing and produce a more cleanable, featureless, smooth surface finish. The need to electropolish a surface is dependent upon...

Dec 11, 2011

Is electropolishing actually necessary given that a 1.0 or greater Cr/Fe ratio can be achieved by passivation alone? The short answer? If a 1.0 Cr/Fe ratio is all you are trying to achieve, no it is not. Now for the long answer. First, the 1.0 or greater Cr/Fe ratio indicated in the ASME BPE standard is a minimal requirement. The best passive and corrosion-resistant surfaces will have a Cr/Fe ratio in excess of 1.5/1, again achievable by passivation alone. The pharmaceutical industry, in most cases, requires a 15-25Ra value typically achieved through a mechanical polishing procedure. It is this procedure that, in my opinion, causes many of the problems experienced today with the formation of the “gray residue” and Class 1 rouge that has plagued end users for years.

Nov 30, 2011

High temperatures, low pH, and aggressive chemicals call for a material that exhibits the high corrosion resistance that traditional stainless steel alloys fail to attain. There are many alloys available to address the corrosion issues; but what makes super-austenitic stainless steel alloy AL-6XN® and nickel alloy C-22 the favorite materials for highly corrosive environments? Are the properties more attractive, or is the availability of the material in the required forms more desirable? Is one better than the other? Both AL-6XN and C-22 have a face-centered cubic lattice structure and contain...

Nov 1, 2011

Welding AL-6XN is a very similar process to welding other stainless steels, but there is one very important exception. This alloy requires an additional alloy to be consumed in the weld. The following video outlines these and other instructions for welding AL-6XN successfully.

Oct 18, 2011

“Purging” is the process of removing air that contains oxygen. Welding is a high-temperature process, so it is very important to keep oxygen and any other gases away from hot metal. We do this to avoid any kind of...

Oct 11, 2011

This brief article will deal with a small part of a much bigger topic: surface finish. We will be looking at commercially available finish options and how they are measured. The surface finish of process systems components plays a very integral role in the cleanability and sterility of the system. The most commonly used unit for surface finish is...