The particular RA (Roughness Average) value is a requirement for stainless vessel manufacturing for federal, state or local compliance agencies across many critical industries. It is a crucial standard in these industries to maintain a clean system. The instrument used in the measurement is called a profilometer, which provides an average in micro inches. The smaller the number, the smoother the stainless material. It is common for high compliance vessels to have single digit RA readings on product contact surfaces.
In the construction of pharmaceutical, life sciences, or medical-use vessels, meeting the RA requirement may include several steps, including material selection, grinding, polishing and chemical finishing. Manufacturing processes can affect the RA measurement on stainless material, including forming, stamping and welding. In the video, we walk out of the manufacturing plant with our quality controls manager to show measurements on material in vessels being manufactured in various stages of production.
Pickle Passivation and Electropolishing chemical finishes have a high degree of improvement on RA smoothness compared to material before it is treated. Pickle passivation, also referred to as descaling, removes the scales and leaves a clean matte finish, free from contamination. Electropolishing is an electrochemical process that dissolves surface metal, removing all embedded contaminants and creates a smooth, mirror finish.
ASTM International (American Standard for Testing and Materials) is one of several standards that Apache upholds. ASTM A967 is the standard specification for Chemical Passivation Treatment for Stainless Parts. ASTM B912 is the standard specification for electropolishing stainless steel alloys. The ASME-Bioprocessing Equipment (BPE) standard was created for the pharmaceutical and bioprocessing industry. The BPE surface finish standard classifies surface finishes and the acceptance criteria for compliance.
In the business of compliance vessels, there are numerous standards that are required to deliver the necessary codes in any given project. Follow our videos, blogs and e-books developed specifically to help our processing customers understand the manufacturing and compliance process.
The main difference between pickle passivation and electropolishing is the appearance and RA (roughness average) of the stainless material. In the photo, an electropolished sample is shown above a pickle passivated sample. The pickle passivated sample has a white appearance, while the electropolished sample has a mirror-like, shiny finish.
Pickle Passivation is the immersion of metal in a pickling bath such as nitric-hydroflouric acid. The process removes metal such as impurities and heat marks from welds.
Electropolishing is an electro-chemical process that removes surface material from stainless steel. The process typically starts with an immersion of the component into a controlled bath of electrolyte that is charged with a DC power supply. Apache’s RA tests show improvements up to 50% smoother, depending on the material.
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