Pickling vs Passivation: What Each One Removes

Chapters

Each chapter opens the video at that point on YouTube.

1. 010:00Pickling vs passivation: what is the difference?

   Pickling vs passivation: two words that often share one line on a stainless pipe order. They are not the same treatment. Each one removes something different from the surface.

2. 020:11What pickling does: chemical descaling of stainless steel

   Zoom into the wall of a stainless pipe. Underneath is the base metal. Heat-related processing can leave scale on the surface. Pickling is a chemical descaling process: its job is to remove that scale. In Junda's published process, pickling is a mill step of its own. Raw material, cold rolling or cold drawing, then solution heat treatment, then pickling, on six pickling systems, then straightening, cutting and inspection.

3. 030:43What passivation does: removing contaminant iron, and how it is tested

   Passivation targets something else: contaminant iron and other foreign matter on the surface. Chemical passivation treatments remove it, and ASTM A967 tests check whether they worked. Different target, different check.

4. 041:02Cleaning, pickling or passivation: match the treatment to the surface condition

   So start from the surface condition, not from the word. Oil, grease or other residues: define the cleanliness and the cleaning method. Scale: define the removal process and the final acceptance. Contaminant iron: define the treatment and how it is verified. A purchase line that only says pickled and passivated sounds complete. But it can leave the internal surface undefined, and the final acceptance undefined. So say which surfaces the requirement covers: the outside, the bore, the ends, the weld regions. State the sampling, the acceptance criteria and the treatment stage. And if later fabrication changes the surface, name who does the final treatment and its verification.

5. 051:49What proves the surface: photos, ASTM A380 and ASTM A967

   Now the evidence. A photograph shows visible condition at one place and one time; it does not prove chemical cleanliness or internal coverage. Citing A380 alone does not certify a mill pickling process: its scope excludes mill descaling as general coverage. And passing an A967 test does not prove compatibility with every process fluid, or a service life. What holds up is the agreed treatment, its scope and the acceptance method, on record.

6. 062:22How to write pickling and passivation into a stainless pipe enquiry

   Mill pickling on its own does not mean an order includes A967 passivation, a test or a roughness value. So the enquiry carries the product, grade and dimensions, the surface condition you need and the treatment specification, and the inspection requirements. Then ask for written confirmation of the proposed process, and any exclusions. Send Junda your grade, dimensions, surface condition and treatment specification for review.