Attitude control system and method for steel pipe to obliquely enter pickling tank

Abstract

The invention provides a posture control system and method for obliquely entering a pickling pool of a steel pipe, and the system comprises a crown block which is used for moving a steel pipe pile to be immersed in the pickling pool; the electric hoist is used for lifting the steel pipe pile; the servo driver is used for adjusting the lifting speed of the steel pipe pile and controlling the posture of the steel pipe pile; the encoder is used for monitoring the lifting speed of the steel pipe pile; the programmable processor is in communication connection with the electric hoist, the crown block, the encoder and the servo driver and is used for controlling the steel pipe pile to be stably immersed into the pickling tank; the two electric hoists are connected with the two ends of the steel pipe pile, the crown block moves the steel pipe pile to the position above the pickling pool, and the electric hoists are driven according to the height value fed back by the encoder so that the steel pipe pile can be immersed into the pickling pool in the posture that one end of the steel pipe pile inclines. And an electric hoist is driven according to the left and right servo drive feedback torque values, so that the steel pipe pile steadily turns to a square posture and is completely immersed in the pickling tank. According to the device, the steel pipe is automatically kept in a stable posture when being obliquely immersed in the pickling tank, and collision is avoided.

Description

Technical Field

[0001] This invention belongs to the field of steel pipe pickling technology, and in particular relates to a posture control system and method for steel pipes obliquely entering a pickling tank. Background Technology

[0002] In the continuous pickling process for steel pipes, bundles of steel pipes need to be immersed in the pickling tank for surface treatment. Existing control systems typically use overhead cranes for hoisting and rely on operator experience or simple program control to lower the steel pipes into the tank in a vertical or near-vertical orientation. However, this method reveals significant limitations when facing the requirements of oblique immersion: due to the lack of real-time perception and compensation for fluid dynamics during immersion, the system cannot effectively cope with the huge asymmetric buoyancy impact generated when the steel pipe cuts into the liquid surface due to the "fluid hammer" effect, and it is also difficult to adapt to the drastic "phase transition" of the system's dynamic characteristics from air to partial immersion and then to full immersion. This leads to the steel pipes being prone to floating, drifting, and loss of attitude control, posing a risk of collision with the tank body, thus restricting production efficiency and safety. Summary of the Invention

[0003] In view of this, the present invention aims to propose a posture control system and method for steel pipes entering the pickling tank at an angle, so as to realize that the steel pipes automatically maintain a stable posture and avoid collision when immersed in the pickling tank at an angle.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A posture control system for steel pipes entering an acid pickling tank at an angle.

[0006] Furthermore, including,

[0007] The overhead crane located above the pickling tank is used to move the steel pipe stacks into the pickling tank.

[0008] Two electric hoists installed on the left and right sides of the overhead crane are used to lift and lower the steel pipe stacks;

[0009] The electric hoist has left and right servo drives that can be raised and lowered, which are used to adjust the lifting speed of the steel pipe stack and control the attitude of the steel pipe stack.

[0010] An encoder installed on the electric hoist is used to monitor the lifting speed of the steel pipe stack;

[0011] A programmable processor, which communicates with electric hoists, overhead cranes, encoders, and servo drives, is used to control the stable immersion of steel pipe stacks into the pickling tank.

[0012] Two electric hoists are connected to both ends of the steel pipe stack. The overhead crane moves the steel pipe stack above the pickling tank. Based on the height value fed back by the encoder, the electric hoists are driven to immerse the steel pipe stack in the pickling tank with one end tilted. During the process of immersing the steel pipe stack in the pickling tank, the electric hoists are driven to smoothly turn the steel pipe stack to a square position and fully immerse it in the pickling tank based on the torque values ​​fed back by the two servo drives on the left and right sides.

[0013] Furthermore, the attitude control method for steel pipes entering the pickling tank at an angle, based on the aforementioned attitude control system for steel pipes entering the pickling tank at an angle, includes the following steps:

[0014] S1. The overhead crane moves the steel pipe stack above the pickling tank. Based on the real-time torque value fed back by the servo drive and the encoder height value, it is determined that the steel pipe stack is in a non-swaying state.

[0015] S2. Control the electric hoist on one side to lower the steel pipe stack so that it is tilted until the height difference fed back by the encoders on both sides reaches the preset value.

[0016] S3. Adjust the servo driver to lower the steel pipe stack using the electric hoists on both sides.

[0017] The steel pipe stack should be lowered while still tilted, without being immersed in the pickling tank.

[0018] When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not, control the electric hoists on both sides to lower the steel pipe stack until the steel pipe stack is laid flat.

[0019] When the steel pipe stack is not fully immersed in the pickling tank but is in a flat position, proceed to S4; when the steel pipe stack is fully immersed in the pickling tank and is in a flat position, proceed to S5.

[0020] S4. Control the electric hoists on both sides of the steel pipe stack to uniformly pulse and jog as the steel pipe stack is lowered into the pickling tank until the steel pipe stack is completely immersed in the pickling tank.

[0021] S5. By adjusting the servo drive, the electric hoists on both sides are used to smoothly and uniformly lower the steel pipe stack to the set depth of the pickling tank, while maintaining the flat position of the steel pipe stack.

[0022] Furthermore, in S1, the attitude of the steel pipe stack is considered to be stable when the torque values ​​of the servo drives on both sides and the encoder height values ​​remain stable.

[0023] Furthermore, in S2, the programmable processor stores the tilt angles of steel pipes of different masses and lengths that are inclined into the pickling tank, and controls the electric hoist on one side to descend to the target height according to the tilt angle.

[0024] Furthermore, S3 includes:

[0025] S31. By adjusting the servo drive, control the electric hoists on both sides to descend simultaneously and at the same speed, so that the steel pipe stack is lowered at the set tilt angle until it contacts the pickling tank. When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not immersed in the pickling tank, go to S32. When the steel pipe stack is fully immersed in the pickling tank but is in a tilted position, go to S33.

[0026] S32. Based on the real-time torque difference feedback from the servo drives on both sides, the programmable processor controls the electric hoist on the high side of the steel pipe stack to descend continuously at a uniform speed, while the electric hoist on the low side descends in a pulsed, uniform, jogging motion. The descent speed of the low side electric hoist is lower than that of the high side electric hoist. During this period, the descent speed of the electric hoists on both sides is simultaneously reduced once each time the high and low sides of the steel pipe stack are switched, until the torque difference is continuously stabilized within the error range or the number of times the high and low sides of the steel pipe stack are switched reaches the preset value.

[0027] S33. Stop the descent of the electric hoist on the lower side of the steel pipe stack. The programmable processor controls the electric hoist on the higher side of the steel pipe stack to descend at a constant speed until the torque difference or height difference is lower than the preset value. Send a rising edge signal to stop the descent of the electric hoist on the higher side of the steel pipe stack.

[0028] Furthermore, in S32, the descent motion curve of the high and low side electric hoists is as follows:

[0029] ;

[0030] In the formula, The descent speed of the high-side electric hoist, The descent speed of the low-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse.

[0031] Furthermore, in S33, the descent motion curve of the high-side electric hoist is as follows:

[0032] ;

[0033] In the formula, The descent speed of the high-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse.

[0034] Furthermore, in S4, the electric hoists on both sides synchronously jog downwards, with the descent speed and jogging duration being the same.

[0035] Furthermore, in S3, when the steel pipe stack descends in an inclined posture, if the torque difference between the two servo drives changes continuously, it is determined that the lower side of the steel pipe stack has contacted the pickling tank, while the higher side of the steel pipe stack has not yet contacted the pickling tank.

[0036] Compared with the prior art, the attitude control system and method for steel pipes obliquely entering the pickling tank described in this invention have the following advantages:

[0037] (1) The attitude control system described in this invention is based on standard industrial equipment such as overhead cranes, electric hoists, servo drives, encoders and their built-in sensor signals. It constructs a decision-making mechanism for multi-sensor information fusion, which combines torque difference, height difference, absolute position of encoder and the time domain characteristics of these signals to realize direct perception and compensation of nonlinear fluid force. It automatically completes the entire process from "identifying stability", "establishing tilt angle", "counteracting fluid disturbance", "leveling" to "complete immersion", greatly improving work efficiency and consistency.

[0038] (2) The attitude control method described in this invention adopts a composite control strategy of "state machine + pulse jogging" to achieve smooth and stable phase transition of attitude. In the partial immersion stage where dynamics change drastically, differentiated speed control of "high-side uniform speed + low-side pulse" is adopted; in the full immersion leveling stage, "high-side single-sided pulse" control is adopted to avoid the problem of single controller parameter failure and make attitude adjustment smoother.

[0039] (3) The attitude control method described in this invention adopts a differentiated speed strategy of "continuous uniform speed on the high side and pulse jogging on the low side" during the critical stage of steel pipe immersion. Each time the high and low sides of the steel pipe stack change position, the descent speed of the electric hoists on both sides is reduced at the same time, so that the disturbance of the entire attitude adjustment stage continues to converge. Even if the pulse frequency and speed are not set to the optimal parameters, the descent speed is reduced according to the strategy of reducing the descent speed during the high and low side change position. The oscillation assignment continues to converge during the oscillation change process of the final flat posture and tilted posture, so that the steel pipe stack finally converges to the flat posture. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0041] Figure 1 This is a schematic diagram of the attitude control method for steel pipes entering the pickling tank at an angle, as described in an embodiment of the present invention. Detailed Implementation

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0043] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0046] The attitude control system for steel pipes inclined into the pickling tank includes: an overhead crane located above the pickling tank for moving the steel pipe stack into the pickling tank; two electric hoists installed on the left and right sides of the overhead crane for raising and lowering the steel pipe stack; left and right servo drives that drive the electric hoists to adjust the raising and lowering speed of the steel pipe stack and control the attitude of the steel pipe stack; encoders installed on the electric hoists for monitoring the raising and lowering speed of the steel pipe stack; and a programmable processor that communicates with the electric hoists, overhead crane, encoders, and servo drives to control the stable immersion of the steel pipe stack into the pickling tank. The process of using an overhead crane to lift steel pipes and immerse them in the pickling tank includes: a pile of steel pipes is bundled together and connected to both ends of the pile by two electric hoists, which are then lifted horizontally. The overhead crane moves the pile of steel pipes above the pickling tank. Based on the height value fed back by the encoder, the electric hoists on both sides are driven to descend at unequal speeds, causing the pile of steel pipes to be immersed in the pickling tank with one end tilted. During the immersion process, the electric hoists are driven by the torque values ​​fed back by the two servo drives on the left and right sides to smoothly turn the pile of steel pipes to a square position and fully immerse it in the pickling tank. This solves the problem of violent swaying caused by buoyancy when multiple hollow steel pipes are immersed in the pickling tank, while also providing a higher descent immersion speed to improve pickling efficiency.

[0047] Example 1 illustrates a posture control method for steel pipes entering an acid pickling tank at an angle, based on the aforementioned posture control system. The posture control method is implemented using a programmable processor (PLC1500 series) as the development environment.

[0048] like Figure 1 As shown, the attitude control method includes the following steps:

[0049] S1. The overhead crane moves the steel pipe stack above the pickling tank. Based on the real-time torque value fed back by the servo drive and the encoder height value, it is determined that the steel pipe stack is in a non-swaying state. When the steel pipe stack is not swaying, the next action is performed.

[0050] S2. Control the electric hoist on one side to lower the steel pipe stack so that it is tilted until the height difference fed back by the encoders on both sides reaches the preset value, so that the steel pipe stack is tilted.

[0051] S3. Adjust the servo driver to lower the steel pipe stack using the electric hoists on both sides.

[0052] The steel pipe stack should be lowered while still tilted, without being immersed in the pickling tank.

[0053] When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not, control the electric hoists on both sides to lower the steel pipe stack until the steel pipe stack is laid flat.

[0054] When the steel pipe stack is not fully immersed in the pickling tank but is in a flat position, proceed to S4; when the steel pipe stack is fully immersed in the pickling tank and is in a flat position, proceed to S5.

[0055] S4. Control the electric hoists on both sides of the steel pipe stack to uniformly pulse and jog down the steel pipe stack until the steel pipe stack is completely immersed in the pickling tank. The electric hoists on both sides jog down synchronously, and the descent speed and jogging duration are the same.

[0056] S5. By adjusting the servo drive, the electric hoists on both sides are used to smoothly and uniformly lower the steel pipe stack to the set depth of the pickling tank, while maintaining the flat position of the steel pipe stack.

[0057] In another embodiment, in S1, the attitude of the steel pipe stack is considered to be stable when the torque values ​​of the servo drives on both sides and the encoder height values ​​remain stable.

[0058] In another embodiment, in S3, when the steel pipe stack descends in an inclined posture, if a continuous change occurs in the torque difference between the servo drives on both sides, it is determined that the lower side of the steel pipe stack has contacted the pickling tank, while the higher side has not yet contacted the pickling tank. Alternatively, an attitude correction command can be issued when the steel pipe stack visually contacts the pickling tank.

[0059] Optionally, in S2, the programmable processor stores the tilt angles of steel pipes of different masses and lengths as they are tilted into the pickling tank, and controls the electric hoist on one side to descend to the target height based on the tilt angle.

[0060] Furthermore, in S3, the process of immersing the steel pipes in the pickling tank includes the following situations: 1. The steel pipe stack is completely immersed in the pickling tank but its posture has not yet been adjusted to a horizontal position and is still in an inclined position; 2. The steel pipe stack is in a horizontal position but is not completely immersed in the pickling tank (the upper part of the steel pipes is not immersed, while the lower part of the steel pipes is immersed); 3. The steel pipes are not completely immersed in the pickling tank and are in an inclined position. For the above scenarios, S3 also includes the following sub-steps:

[0061] S31. By adjusting the servo drive, control the electric hoists on both sides to descend simultaneously and at the same speed, so that the steel pipe stack is lowered at the set tilt angle until it contacts the pickling tank. When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not immersed in the pickling tank, go to S32. When the steel pipe stack is fully immersed in the pickling tank but is in a tilted position, go to S33.

[0062] S32. Based on the real-time torque difference feedback from the servo drives on both sides, the programmable processor controls the electric hoist on the high side of the steel pipe stack to descend continuously at a uniform speed, while the electric hoist on the low side descends in a pulsed, uniform, jogging motion. The descent speed of the low side electric hoist is lower than that of the high side electric hoist. During this period, the descent speed of both electric hoists is simultaneously reduced once each time the high and low sides of the steel pipe stack shift, until the torque difference remains stable within the error range or the number of shifts between the high and low sides of the steel pipe stack reaches a preset value. The advantage is that while maintaining the descent speed of both electric hoists, the attitude of the steel pipe stack is adjusted according to the descent speed difference. Furthermore, the jogging descent on the low side during the descent controls the large-scale shaking caused by the pickling liquid poured into the steel pipe. Its greatest advantage is that the descent speed of both electric hoists is reduced simultaneously each time the high and low sides of the steel pipe stack shift, so that the disturbance during the entire attitude adjustment stage continues to converge. Even if the pulse frequency and speed are not set to the optimal parameters, the strategy of reducing the descent speed during the high and low side shifts continuously converges the oscillation assignment during the oscillation changes between the final flat and tilted attitudes, so that the steel pipe stack eventually converges to a flat attitude.

[0063] S33. Stop the descent of the low-side electric hoist of the steel pipe stack. The programmable processor controls the high-side electric hoist of the steel pipe stack to descend at a constant speed until the torque difference or height difference is lower than the preset value. Send a rising edge signal to stop the descent of the high-side electric hoist of the steel pipe stack. The advantage is that for the steel pipe stack that has been fully submerged, the shaking force mainly comes from the axial force of the high-side descent to adjust the attitude. Therefore, the high-side steel pipe is descended at a constant speed to control the disturbance amplitude of the steel pipe stack.

[0064] Specifically, in S32, the descent motion curve of the high and low side electric hoists is as follows:

[0065] ;

[0066] In the formula, The descent speed of the high-side electric hoist, The descent speed of the low-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse. The pulse frequency should be set to a low frequency, and the pulse signal duration should be short with a slow descent rate.

[0067] Specifically, in S33, the descent motion curve of the high-side electric hoist is as follows:

[0068] ;

[0069] In the formula, The descent speed of the high-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse. The pulse frequency should be high, and the pulse signal should have a long duration and a rapid descent rate.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A posture control system for steel pipes inclined into a pickling tank, characterized in that: include, The overhead crane located above the pickling tank is used to move the steel pipe stacks into the pickling tank. Two electric hoists installed on the left and right sides of the overhead crane are used to lift and lower the steel pipe stacks; The electric hoist has left and right servo drives that can be raised and lowered, which are used to adjust the lifting speed of the steel pipe stack and control the attitude of the steel pipe stack. An encoder installed on the electric hoist is used to monitor the lifting speed of the steel pipe stack; A programmable processor, which communicates with electric hoists, overhead cranes, encoders, and servo drives, is used to control the stable immersion of steel pipe stacks into the pickling tank. Two electric hoists are connected to both ends of the steel pipe stack. The overhead crane moves the steel pipe stack above the pickling tank. Based on the height value fed back by the encoder, the electric hoists are driven to immerse the steel pipe stack in the pickling tank with one end tilted. During the process of immersing the steel pipe stack in the pickling tank, the electric hoists are driven to smoothly turn the steel pipe stack to a square position and fully immerse it in the pickling tank based on the torque values ​​fed back by the two servo drives on the left and right sides.

2. A posture control method for steel pipes entering a pickling tank at an angle, based on the posture control system for steel pipes entering a pickling tank at an angle as described in claim 1, characterized in that: Includes the following steps: S1. The overhead crane moves the steel pipe stack above the pickling tank. Based on the real-time torque value fed back by the servo drive and the encoder height value, it is determined that the steel pipe stack is in a non-swaying state. S2. Control the electric hoist on one side to lower the steel pipe stack so that it is tilted until the height difference fed back by the encoders on both sides reaches the preset value. S3. Adjust the servo driver to lower the steel pipe stack using the electric hoists on both sides. The steel pipe stack should be lowered while still tilted, without being immersed in the pickling tank. When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not, control the electric hoists on both sides to lower the steel pipe stack until the steel pipe stack is laid flat. When the steel pipe stack is not fully immersed in the pickling tank but is in a flat position, proceed to S4; when the steel pipe stack is fully immersed in the pickling tank and is in a flat position, proceed to S5. S4. Control the electric hoists on both sides of the steel pipe stack to uniformly pulse and jog as the steel pipe stack is lowered into the pickling tank until the steel pipe stack is completely immersed in the pickling tank. S5. By adjusting the servo drive, the electric hoists on both sides are used to smoothly and uniformly lower the steel pipe stack to the set depth of the pickling tank, while maintaining the flat position of the steel pipe stack.

3. The posture control method for steel pipes obliquely entering the pickling tank according to claim 2, characterized in that: In S1, the attitude of the steel pipe stack is considered to be stable when the torque values ​​of the servo drives on both sides and the encoder height values ​​remain stable.

4. The posture control method for steel pipes obliquely entering the pickling tank according to claim 2, characterized in that: In S2, the programmable processor stores the tilt angles of steel pipes of different masses and lengths that are inclined into the pickling tank, and controls the electric hoist on one side to descend to the target height according to the tilt angle.

5. The posture control method for steel pipes obliquely entering the pickling tank according to claim 2, characterized in that: The S3 includes: S31. By adjusting the servo drive, control the electric hoists on both sides to descend simultaneously and at the same speed, so that the steel pipe stack is lowered at the set tilt angle until it contacts the pickling tank. When the lower side of the steel pipe stack is immersed in the pickling tank but the higher side is not immersed in the pickling tank, go to S32. When the steel pipe stack is fully immersed in the pickling tank but is in a tilted position, go to S33. S32. Based on the real-time torque difference feedback from the servo drives on both sides, the programmable processor controls the electric hoist on the high side of the steel pipe stack to descend continuously at a uniform speed, while the electric hoist on the low side descends in a pulsed, uniform, jogging motion. The descent speed of the low side electric hoist is lower than that of the high side electric hoist. During this period, the descent speed of the electric hoists on both sides is simultaneously reduced once each time the high and low sides of the steel pipe stack are switched, until the torque difference is continuously stabilized within the error range or the number of times the high and low sides of the steel pipe stack are switched reaches the preset value. S33. Stop the descent of the electric hoist on the lower side of the steel pipe stack. The programmable processor controls the electric hoist on the higher side of the steel pipe stack to descend at a constant speed until the torque difference or height difference is lower than the preset value. Send a rising edge signal to stop the descent of the electric hoist on the higher side of the steel pipe stack.

6. The posture control method for steel pipes obliquely entering the pickling tank according to claim 5, characterized in that: In S32, the descent motion curve of the high and low side electric hoists is as follows: ； In the formula, The descent speed of the high-side electric hoist, The descent speed of the low-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse.

7. The posture control method for steel pipes obliquely entering the pickling tank according to claim 5, characterized in that: In S33, the descent motion curve of the high-side electric hoist is as follows: ； In the formula, The descent speed of the high-side electric hoist, To set a constant speed value, The pulse velocity amplitude, The duration of a single pulse. For unit step function, This refers to the number of pulse triggers. For electric hoists The start time of the next pulse. This is the current pulse.

8. The posture control method for steel pipes obliquely entering the pickling tank according to claim 2, characterized in that: In S4, the electric hoists on both sides move down synchronously in jogs, with the descent speed and jog duration being the same.

9. The posture control method for steel pipes obliquely entering the pickling tank according to claim 2, characterized in that: In S3, when the steel pipe stack descends in an inclined posture, if the torque difference between the two servo drives changes continuously, it is determined that the lower side of the steel pipe stack has contacted the pickling tank, while the higher side of the steel pipe stack has not yet contacted the pickling tank.

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