What are the acceptance criteria and precautions for pickling?
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What are the acceptance criteria and precautions for pickling?
Acceptance criteria: 1. The surface should have a uniform silver-white color. 2. The surface must be free of oxides, mechanical impurities, and dirt, as well as any scratches. There shall be no grinding marks on the metal surface outside the weld. 3. The surface must not show any obvious traces of corrosion, nor any patches with uneven coloring or significant color differences; the weld surface must be free of oxidized colors. There shall be no signs of excessive corrosion such as pitting. 4. The heat exchanger tube joints and surrounding tube sheets must be free of any signs of corrosion. 5. No moisture is allowed to remain anywhere. 6. Pickling and passivation paste should be purchased from well-known brands, or a paste with better performance can be prepared manually.
Pay attention to the temperature and reaction time; I’ve seen cases where, during the first attempt, the pickling process resulted in marks similar to water stains due to slow reaction times and low temperatures. It was later determined that low temperatures prevented a complete reaction, and inadequate rinsing with water also contributed to this issue.