Specify the measured surface
Ra describes a surface-profile parameter measured under defined conditions. State whether the requirement applies to vessel walls, welds, valve parts or all product-contact surfaces. Include measurement method, sampling plan and acceptance documentation. A polished photograph cannot demonstrate a numerical Ra value.
Read the SINOSEN option correctly
The supplied technical brief includes a mirror-finish option with a target Ra of 0.1–0.2 µm. This is an optional manufacturing and inspection requirement to agree for the project. It is not automatically the finish of every standard skid, and it is not a claim of an independently certified hygienic assembly.
Examine geometry and drainage
A smooth wall can still be part of a poorly drainable system. Review crevices, gasket protrusions, dead spaces, weld condition, instrumentation and the way cleaning fluid reaches each surface. Valve cavities and branch connections deserve attention because a vessel-only inspection can overlook them.
Link finish to a practical quality plan
Ask which measurements are supplied, how weld areas are assessed and how the final equipment is protected during transport. The plant should also define cleaning verification under actual product conditions. The useful specification combines achievable finish, cleanable geometry, compatible materials and documented acceptance. Requesting the lowest possible roughness number without this context can add cost without answering the main hygiene question.
General engineering guidance. Numerical examples are illustrative; project specifications and acceptance criteria are agreed for the actual duty.