Does stainless steel static equipment have to be pickled?
Thread Content
Static equipment such as stainless steel towers and heat exchangers does not have to be pickled. Whether to implement it needs to be comprehensively judged based on the surface condition of the equipment, usage scenarios and industry requirements. Scenarios where pickling is recommended: After the equipment undergoes high-temperature processing such as welding and heat treatment, oxide scale and welding slag will form on the surface. Pickling can completely remove these impurities, prevent them from damaging the stainless steel passivation film, and improve the corrosion resistance of the equipment. It is used in chemical, food, pharmaceutical and other industries that have high requirements on hygiene and corrosion resistance. Pickling and passivation processes can form a dense protective film to meet industry specifications and extend the service life of equipment. After long-term use, the surface area has accumulated rust and stubborn dirt. Pickling can be used as a maintenance method to restore the original performance of the equipment. Scenario equipment that does not require pickling has a clean surface, no oxide layer and pollutants, and a complete passivation film after leaving the factory. The use environment has no strong corrosion and no special hygiene requirements, and can be put into use directly. For short-term, cost-sensitive equipment with minimal surface contamination, the pickling step can be omitted if the contaminants do not affect normal operation. The pickling operation requires corrosion inhibitors, subsequent passivation and environmentally friendly wastewater treatment to avoid excessive corrosion of the equipment or environmental risks.
I read this post by the original poster and summarized it well. It is true that we cannot say across the board that pickling is necessary. The key depends on the working conditions. I would like to add two points of personal experience:: The heat-affected zone of welding is often a weak link in the corrosion of stainless steel. Even if the whole is not pickled, it is recommended to at least partially treat the weld bead area. Brushing it with stainless steel pickling passivation paste can clean off the thermally induced oxide scale and chromium-poor layer, effectively reducing the risk of intergranular corrosion. If the water stored after the hydrostatic test is not drained, pitting corrosion may also occur in a low chlorine environment. It is recommended that the equipment be rinsed with deionized water in time after cleaning, and if possible, followed by neutralization treatment to better ensure the integrity of the passivation film. In addition, the poster mentioned that "the surface area accumulates rust after long-term use". In fact, many times it is not the stainless steel itself that rusts, but the "fake rust" caused by carbon steel dust or chloride ion pollution sources attached to the surface. The pickling cleaning effect will be very good, but be careful not to exceed the concentration and temperature of the pickling solution to prevent excessive corrosion. For your reference, it depends on the equipment material (304 or 316L? ), medium environment (how much chlorine does it contain? ) and the customer's technical agreement requirements to make decisions.