Tubing Surface Finishes for Nickel Alloy and Stainless Steel
The outside diameter (OD) of random length stainless steel or nickel alloy tubing is typically offered in 3 finishes.
The most common finish is the drawn finish, which is the finish that results from the stainless tube passing through the final die in the die sequence. Provided the die itself is in acceptable condition, a drawn finish will be bright and smooth with surface finishes typically considerably better than 16 Ra. Some minor imperfections like swirl marks from straightening can be present however these are normally faint and aesthetic in nature only. Failure to use an acceptable quality die for the final die can result in die scratches or marks on the tubing which are undesirable.
Centerless ground finish tubing results in more of a matte appearing finish, but a measurably improved surface finish, often less than 8 Ra. Centerless ground finish is offered when requested by the customer or in certain circumstances is required in order to meet tolerancing requirements.
A polished finish is achieved by running the tubing through custom-designed polishing machinery. The most expensive of the three main options, it yields a bright and highly blended, smooth finish. However, because of the nature of the process, which is slower than grinding, the cost is higher.
Required tubing OD finish is highly dependent on the application and should be specified by the customer when requesting a quotation. Consider if a specialized finish is essential, otherwise selecting one will increase the price of the tubing. It’s important to note that for stainless steel tubular fabricated parts, other finishing processes like electropolishing are available, too.