Can stainless steel pipe fittings be heated during pickling?
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To improve efficiency, can the pickling tank for stainless steel fittings be heated?
2 Pohang No. 3 Annealing and Pickling Line: The Pohang No. 3 Annealing and Pickling Line was supplied by VAI Company. Its designed processing capacity is 450,000 tons per year for hot-rolled strip steel, and 50,000 tons per year for cold-rolled strip steel made of austenitic and ferritic stainless steels. Together with the existing annealing and pickling lines for hot-rolled strip No. 1 and No. 2, this set of equipment will enable Pohang’s capacity to process hot-rolled strip to exceed 1.6 million tons per year. Table 2: Key Process Data – Strip Data
Materials: Austenitic, ferritic, and martensitic stainless steels
Strip thickness: 1.0–5.0 (hot-rolled); 1.0–2.0 (cold-rolled)
Strip width/mm: 600–1300
Production capacity/t/year: 500,000
Strip speed: Inlet section/m.min: 130; Process section/m.min: 80 (hot-rolled) / 100 (cold-rolled); Outlet section/m.min: 130
Anode furnace capacity/t.h: 111 (for 304-type stainless steel with a width of 130 mm)
TV value*: 180
Coil dimensions: Outer diameter/mm: 2100; Inner diameter/mm: 762/610 (inlet section), 610 (exit section); Coil weight/t: 25 (maximum)
When designing this line and its associated equipment, the length of the production line was limited by existing buildings. Through careful design and rational arrangement, the layout of Line 3 has become a model for modern annealing and pickling lines. The main equipment and process flow are shown in Figure 3, while the key process parameters are listed in Table 2. 2.1 Inlet section: The inlet section is equipped with two uncoilers; each uncoiler comes complete with its own feeding, straightening, and cutting equipment in order to prepare the coil ends in a format suitable for welding operations. A welding machine is a cut-arc device that uses the MIG welding process. The machine includes a fixed shear and a transverse gripper that clamp the two tails before the cutting operation, releasing the rolled piece only after the welding cycle is completed, thereby ensuring stable and reliable alignment of the tails. The 4-layer horizontal loop is arranged in a pit beneath the furnace section, and it has a material storage capacity of 4 minutes at a maximum process speed of 100 m/min. The loop is composed of a main trolley and some movable support trolleys. The main feature of the system is that when the loop is full, each moving support cart moves away one by one and is held in place by a special cam mechanism; this mechanism prevents them from moving out of position until the loop is empty, at which point the main cart collects the support carts. 2.2 Process Section The process section consists of an annealing furnace, cooling equipment, a roller descaling machine, and a pickling section. The furnace section is arranged horizontally and uses natural gas as fuel; a continuous tunnel type is adopted to achieve the highest operational efficiency. The furnace includes a first stage of radiant preheating, followed by three direct-fired heating stages. The preheating section uses the combustion gases from the direct-fired heating section to preheat the steel strip to around 440°C before it enters the direct-fired heating section. Disc-type roller bed support components are provided between different furnace sections to enable rapid roller replacement. Each disc roller assembly is equipped with two ceramic fiber cover support rollers. Next is heat treatment, during which a specially designed, all-water-based grade 5 quenching system is used to cool the steel strip to a final outlet temperature of no more than 80°C. The wet descaling machine, combined with water spraying technology, can wash away dust and iron scale from the surface of the steel strip as well as from the machine itself; compared to dry descaling machines, it helps to keep the area around the machine cleaner. Due to the bending of the strip around the small-diameter working rolls, a high tension is generated in the inlet and outlet roller tensioning devices, which effectively removes scale. This allows the material to enter the shot blasting and pickling sections in a relatively straight state, thereby ensuring that these subsequent descaling equipment can operate very efficiently. The processing line has a processing capacity of 111 t/h at a maximum process speed of 100 m/min and a strip width of 1300 mm; a line with such capacity typically requires a building length of around 480 m. However, in this case, the maximum usable length is 400m. To accommodate this limitation, the pickling section, approximately 160m in length, was constructed in two layers. The layer below consists of two sulfuric acid pickling tanks, the first of which contains electrodes. At the outlet of the second sulfuric acid tank, the steel strip passes vertically around a two-roll reversing device, and then turns back to enter a scrubber before going into the first of the three acid mixing tanks. With this arrangement, the pickling section is reduced to about half of the normal required length. Devices that require regular attention, such as the scrubbers, are located on the upper level to facilitate roll replacement and maintenance. The export section includes an exit loop, a 4-roll leveler, an inspection station, a winding station that combines automatic coil bundling and weighing, and a walking beam conveyor system for coil storage and transportation. 2.3 Wastewater treatment equipment: The wastewater treatment equipment is used to treat the waste liquids from Lines 1 and 3 for annealing and pickling, and it includes conventional treatment steps such as neutralizing the waste liquids and adjusting the final solution to make it suitable for discharge into the drainage system. The wastewater treatment equipment can process approximately 1,000 m3 of water per hour; this water comes from the water quenching areas of Lines 1 and 3, as well as from the make-up water for the wet descaling machine on Line 3. These waters contain a large amount of fine iron scale particles, and if the water is to be reused, these iron scale particles must be removed. The treatment equipment consists of an initial iron scale sedimentation tank equipped with a hydrocyclone, and a second-stage filtration tank using sand as a medium. After final filtration, the water returning to the system must be cooled before it is reused for water quenching and descaling. Two additional factors must also be taken into account for the new water treatment equipment: first, it is necessary to handle the wastewater and cooling water generated by the existing two annealing and pickling lines. Secondly, it must be installed in the location occupied by existing similar equipment on Line 1, without stopping or interrupting the production on Line 1. 3 Conclusion Through the introduction of the KL3 stainless steel cold-rolled strip annealing and pickling line at ThyssenKrupp Nillostack Cliffield Plant and the new No. 3 annealing and pickling line at Pohang, it can be seen that both of these lines are examples of successful renovation projects; they effectively resolved the conflict between processing requirements and space constraints, ensuring smooth production and easy maintenance, thereby achieving the desired results.
Materials: Austenitic, ferritic, and martensitic stainless steels
Strip thickness: 1.0–5.0 (hot-rolled); 1.0–2.0 (cold-rolled)
Strip width/mm: 600–1300
Production capacity/t/year: 500,000
Strip speed: Inlet section/m.min: 130; Process section/m.min: 80 (hot-rolled) / 100 (cold-rolled); Outlet section/m.min: 130
Anode furnace capacity/t.h: 111 (for 304-type stainless steel with a width of 130 mm)
TV value*: 180
Coil dimensions: Outer diameter/mm: 2100; Inner diameter/mm: 762/610 (inlet section), 610 (exit section); Coil weight/t: 25 (maximum)
When designing this line and its associated equipment, the length of the production line was limited by existing buildings. Through careful design and rational arrangement, the layout of Line 3 has become a model for modern annealing and pickling lines. The main equipment and process flow are shown in Figure 3, while the key process parameters are listed in Table 2. 2.1 Inlet section: The inlet section is equipped with two uncoilers; each uncoiler comes complete with its own feeding, straightening, and cutting equipment in order to prepare the coil ends in a format suitable for welding operations. A welding machine is a cut-arc device that uses the MIG welding process. The machine includes a fixed shear and a transverse gripper that clamp the two tails before the cutting operation, releasing the rolled piece only after the welding cycle is completed, thereby ensuring stable and reliable alignment of the tails. The 4-layer horizontal loop is arranged in a pit beneath the furnace section, and it has a material storage capacity of 4 minutes at a maximum process speed of 100 m/min. The loop is composed of a main trolley and some movable support trolleys. The main feature of the system is that when the loop is full, each moving support cart moves away one by one and is held in place by a special cam mechanism; this mechanism prevents them from moving out of position until the loop is empty, at which point the main cart collects the support carts. 2.2 Process Section The process section consists of an annealing furnace, cooling equipment, a roller descaling machine, and a pickling section. The furnace section is arranged horizontally and uses natural gas as fuel; a continuous tunnel type is adopted to achieve the highest operational efficiency. The furnace includes a first stage of radiant preheating, followed by three direct-fired heating stages. The preheating section uses the combustion gases from the direct-fired heating section to preheat the steel strip to around 440°C before it enters the direct-fired heating section. Disc-type roller bed support components are provided between different furnace sections to enable rapid roller replacement. Each disc roller assembly is equipped with two ceramic fiber cover support rollers. Next is heat treatment, during which a specially designed, all-water-based grade 5 quenching system is used to cool the steel strip to a final outlet temperature of no more than 80°C. The wet descaling machine, combined with water spraying technology, can wash away dust and iron scale from the surface of the steel strip as well as from the machine itself; compared to dry descaling machines, it helps to keep the area around the machine cleaner. Due to the bending of the strip around the small-diameter working rolls, a high tension is generated in the inlet and outlet roller tensioning devices, which effectively removes scale. This allows the material to enter the shot blasting and pickling sections in a relatively straight state, thereby ensuring that these subsequent descaling equipment can operate very efficiently. The processing line has a processing capacity of 111 t/h at a maximum process speed of 100 m/min and a strip width of 1300 mm; a line with such capacity typically requires a building length of around 480 m. However, in this case, the maximum usable length is 400m. To accommodate this limitation, the pickling section, approximately 160m in length, was constructed in two layers. The layer below consists of two sulfuric acid pickling tanks, the first of which contains electrodes. At the outlet of the second sulfuric acid tank, the steel strip passes vertically around a two-roll reversing device, and then turns back to enter a scrubber before going into the first of the three acid mixing tanks. With this arrangement, the pickling section is reduced to about half of the normal required length. Devices that require regular attention, such as the scrubbers, are located on the upper level to facilitate roll replacement and maintenance. The export section includes an exit loop, a 4-roll leveler, an inspection station, a winding station that combines automatic coil bundling and weighing, and a walking beam conveyor system for coil storage and transportation. 2.3 Wastewater treatment equipment: The wastewater treatment equipment is used to treat the waste liquids from Lines 1 and 3 for annealing and pickling, and it includes conventional treatment steps such as neutralizing the waste liquids and adjusting the final solution to make it suitable for discharge into the drainage system. The wastewater treatment equipment can process approximately 1,000 m3 of water per hour; this water comes from the water quenching areas of Lines 1 and 3, as well as from the make-up water for the wet descaling machine on Line 3. These waters contain a large amount of fine iron scale particles, and if the water is to be reused, these iron scale particles must be removed. The treatment equipment consists of an initial iron scale sedimentation tank equipped with a hydrocyclone, and a second-stage filtration tank using sand as a medium. After final filtration, the water returning to the system must be cooled before it is reused for water quenching and descaling. Two additional factors must also be taken into account for the new water treatment equipment: first, it is necessary to handle the wastewater and cooling water generated by the existing two annealing and pickling lines. Secondly, it must be installed in the location occupied by existing similar equipment on Line 1, without stopping or interrupting the production on Line 1. 3 Conclusion Through the introduction of the KL3 stainless steel cold-rolled strip annealing and pickling line at ThyssenKrupp Nillostack Cliffield Plant and the new No. 3 annealing and pickling line at Pohang, it can be seen that both of these lines are examples of successful renovation projects; they effectively resolved the conflict between processing requirements and space constraints, ensuring smooth production and easy maintenance, thereby achieving the desired results.
The operational steps for pickling and passivating stainless steel welded pipes are divided into the following eight points: provided by Liaoning Tailang Stainless Steel Co., Ltd. I. Preparation work II. Chemical degreasing 1) Chemical degreasing is carried out by immersion in a tank; the degreasing tank is made of steel plates, with its inner walls lined with PVC or polyethylene. 2) Perform chemical degreasing using 12–15% nitric acid (by volume) at a temperature of 40°C–60°C for 2–4 hours. 3) When the pipe fittings are immersed in the tank, attention should be paid to their placement to prevent air from remaining inside the pipes. 4) During the soaking process, the pipe fittings should be moved up and down, forward and backward, or turned over, so as to continuously renew the solution in the inner cavity and improve the effectiveness. If necessary, remove the fittings, rinse them with water and air, and then soak them. 5) Perform chemical degreasing until the surface of the fittings is completely wetted by water. III. Rinsing with hot water 1) The oil-removed fittings are taken out of the degreasing tank and immersed in a hot water tank at a temperature of around 40°C to 60°C for rinsing, for a time of 5 to 20 minutes. 2) The hot water tank is made of steel plates, with the inner wall lined with PVC or polyethylene. 3) The chloride ion content in water is less than 25 ppm. IV. Rinsing with water 1) The fittings that have been rinsed with water should be washed further using pressurized water (pressure P≥0.1Mpa). 2) The chloride ion content in water is less than 25 ppm. V. Passivation 1) Passivation is carried out using a tank with bubbles; the formula for the passivation solution and the immersion time can be chosen from either option in Table 2.3. 2) Fabrication of the passivation tank steel plates, with acid-resistant plastic lining on the inner wall. 3) When soaking in the groove, pay attention to the placement to avoid air remaining inside the tube. 4) During the soaking process, the pipe fittings should be moved up and down, forward and backward, or turned over, so as to continuously renew the solution in the inner cavity and improve the effectiveness. If necessary, remove the fittings, rinse them with water and air, and then soak them. VI. Drying: The passivated fittings must be promptly dried using clean compressed air or nitrogen, and sufficient time (at least 2 hours) must be allowed for them to naturally re-passivate in the air. VII. Inspection: After passivation, the pipe fittings should be inspected internally and mutually, and then submitted to the quality inspector for acceptance in accordance with the requirements. VIII. Protection 1) For fittings whose outer surfaces require painting, proceed in accordance with the painting requirements. 2) After passing the inspection, the fittings are sealed with plastic plugs, wrapped with weatherproof cloth for protection, and labeled
Reply to the original poster: 1. Personally, I think there’s no need to heat it; it’s bad for the environment, and there are many factors that affect cleaning efficiency. 2. If you want to heat it, you need to consider what type of acid it is in order to decide whether heating is appropriate. If it’s nitric acid, as mentioned earlier, the temperature should not be too high; you can refer to the temperature guidelines provided earlier. Many acids used for cleaning stainless steel are volatile, and heating accelerates their evaporation. Of course, some mist suppressants can be added in such cases. 3. If heating is required, in addition to considering the components and requirements of the cleaning agent, it is also necessary to check whether the pickling tank can withstand heating. Reply to the person above: 1. Nitric acid at around 12%, at a temperature of about 40 degrees Celsius, has very poor oil-removal capabilities; it takes 2–4 hours to achieve the desired results. This formula is generally not used for oil removal – it is mainly intended for removing welding oxide scale. Moreover, the person above did not mention any steps for removing welding oxide scale or the appropriate ratio of ingredients for the cleaning solution.