Quenching tank system and method of use

Abstract

A quenching tank system includes a cooling tank having an entrance opening adapted to allow a first portion of a heated continuous tube to enter the cooling tank and to allow a first portion of a cooling fluid in the tank to flow out the entrance opening. The cooling tank includes an exit opening adapted to allow a partially cooled second portion of the continuous tube moving through the tank to exit the cooling tank and to allow a second portion of the cooling fluid in the tank to flow out the exit opening. The system also includes a cooling fluid collection and distribution system adapted to collect cooling fluid flowing out of the cooling tank, return the collected cooling fluid to the cooling tank and distribute the cooling fluid in the cooling tank. A method of cooling a heated continuous tube using a quenching tank system is described.

Claims

1. A quenching tank system comprising: a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said entrance opening adapted to allow a first portion of a heated continuous tube to enter the cooling tank through the entrance opening, and said entrance opening further adapted to allow a first portion of a cooling fluid in the cooling tank that has been heated by the first portion of the heated continuous tube entering the cooling tank to flow out the entrance opening, and said exit opening adapted to allow a partially cooled second portion of the heated continuous tube moving through the cooling tank to exit the cooling tank through the exit opening, and said exit opening further adapted to allow a second portion of the cooling fluid in the cooling tank, that has been heated by the second portion of the heated continuous tube in the tank to flow out the exit opening; and said quenching tank system further comprising a cooling fluid collection and distribution system adapted to collect cooling fluid flowing out of the cooling tank, return the collected cooling fluid to the cooling tank and distribute the cooling fluid in the cooling tank, said collection and distribution system including at least one eductor that is adapted to direct a portion of the cooling fluid in the cooling tank toward the entrance end of the cooling tank and out the entrance opening of the cooling tank concurrently with inserting the first portion of the heated continuous tube through the entrance opening.

2. The quenching tank system of claim 1, wherein the cooling fluid collection and distribution system comprises a secondary cooling tank positioned below the cooling tank, said secondary cooling tank adapted to collect the first portion of the cooling fluid flowing out of the entrance opening and the second portion of the cooling fluid flowing out of the exit opening of the cooling tank.

3. The quenching tank system of claim 2, wherein the cooling fluid collection and distribution system further comprises piping connecting the secondary cooling tank to at least one heat exchanger adapted to cool the collected cooling fluid in the secondary cooling tank and return the cooled cooling fluid to the cooling tank.

4. The quenching tank system of claim 1, further comprising a plurality of push rollers and support rollers adapted to guide the heated continuous tube linearly from the entrance end through the cooling tank to the exit end of the cooling tank.

5. The quenching tank system of claim 1, wherein at least a portion of the entrance opening and the exit opening are in a horizontal plane.

6. A quenching tank system comprising: a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said entrance opening adapted to allow a first portion of a heated continuous tube to enter the cooling tank through the entrance opening, and said entrance opening further adapted to allow a first portion of a cooling fluid in the cooling tank that has been heated by the first portion of the continuous heated tube entering the cooling tank to flow out the entrance opening, and said exit opening adapted to allow a partially cooled second portion of the heated continuous tube moving through the cooling tank to exit the cooling tank through the exit opening, and said exit opening further adapted to allow a second portion of the cooling fluid in the tank, that has been heated by the second portion of the heated continuous tube in the cooling tank to flow out the exit opening; and said quenching tank system further comprising a cooling fluid collection and distribution system adapted to collect cooling fluid flowing out of the cooling tank, return the collected fluid to the cooling tank and distribute the cooling fluid in the cooling tank, wherein the cooling fluid collection and distribution system includes a plurality of eductors that are adapted to cause at least a portion of the cooling fluid in the cooling tank to overflow a top of one or more side walls of the cooling tank.

7. The quenching tank system of claim 1 adapted to provide a minimum fluid flow rate of the cooling fluid (Qw) in m.sup.3/s in the cooling fluid collection and distribution system as the heated continuous tube moves through the cooling tank is expressed by a relationship:
Qw>1000×Ss×Vt/DTw wherein Ss is a cross section in square meters of the heated continuous tube being cooled; Vt is a tube speed in m/s; and DTw is a decrease in temperature of the cooling fluid in a heat exchanger in ° C.

8. The quenching tank system of claim 1, wherein a cross section (Sw) of the cooling tank in square meters is defined by a relationship:
Sw>37Ss×Vt×tstop/Lw, wherein Sw is taken in a direction (D) perpendicular to a direction of heated continuous tube movement, relative to a cross section (Ss) in square meters of the heated continuous tube being cooled; and Vt is a continuous tube speed in m/s and tstop is a time of a cessation of cooling in a heat exchanger in seconds.

9. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein; inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; and providing a cooling fluid collection and distribution system including at least one eductor and a secondary cooling tank positioned below the cooling tank; directing with the at least one eductor at least a portion of cooling fluid in the cooling tank toward the entrance opening of the cooling tank concurrently with inserting the first portion of the heated continuous tube through the entrance opening; collecting the first portion and the second portion of the cooling fluid flowing out of the cooling tank in the secondary cooling tank; and returning the collected cooling fluid to the cooling tank and distributing the returned cooling fluid in the cooling tank.

10. The method of claim 9 further comprising: transferring collected cooling fluid from the secondary cooling tank to at least one heat exchanger; cooling the collected cooling fluid in the heat exchanger; and returning the cooled cooling fluid to the cooling tank.

11. The method of claim 9 further comprising: providing a plurality of push rollers and support rollers; and guiding with the push rollers and support rollers the heated continuous tube linearly from the entrance end of the cooling tank through the cooling tank to the exit end of the cooling tank.

12. The method of claim 9 wherein providing the cooling tank further comprises providing at least a portion of the entrance opening and exit opening in a same horizontal plane.

13. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein; inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; flowing the first portion of the cooling fluid out the entrance opening; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; flowing the second portion of the cooling fluid out the exit opening; providing at least one eductor; and directing with the at least one eductor cooling fluid in the cooling tank toward the entrance end of the cooling tank; providing additional eductors; and directing with the additional eductors at least a portion of cooling fluid in the cooling tank to overflow a top of one or more side walls of the cooling tank.

14. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein; inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; flowing the first portion of the cooling fluid out the entrance opening; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; flowing the second portion of the cooling fluid out the exit opening; and forming a 90% marensite by maintaining a minimum relative velocity (Vmin) of movement of the heated continuous tube through the cooling tank with water as the cooling fluid, wherein the water is at a temperature less than or equal to 35° C., said minimum relative velocity (Vmin) of movement in meters per second is calculated by the following equation:
Vmin>1/100+1/145×(WT−2.77)+1/1500×(CR90M−20) wherein a continuous tube wall thickness (WT) in millimeters is between 2.77 mm and 7.11 mm; and a cooling rate (CR90M) is 20 to 50° C. per second.

15. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein; inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; flowing the first portion of the cooling fluid out the entrance opening; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; flowing the second portion of the cooling fluid out the exit opening; and forming a 90% marensite by maintaining a minimum relative velocity (Vmin) of movement of the heated continuous tube through the cooling tank with water as the cooling fluid, wherein the water is at a temperature greater than to 35° C. and less than 60° C., said minimum relative velocity (Vmin) of movement in meters per second is calculated by the following equation
Vmin>1/20+1/45×(WT−2.77)+1/300×(CR90M−20) wherein a continuous tube wall thickness (WT) in millimeters is between 2.77 mm and 7.11 mm; and a cooling rate (CR90M) is between 20 to 50 ° C. per second.

16. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein; inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; flowing the first portion of the cooling fluid out the entrance opening; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; flowing the second portion of the cooling fluid out the exit opening; and forming a 90% marensite by maintaining a minimum fluid flow rate of the cooling fluid (Qw) in m.sup.3in a fluid collection and distribution system necessary to form 90% martensitic as the heated continuous tube moves through the cooling tank is expressed by a relationship:
Qw>1000×Ss×Vt/DT wherein Ss is a cross section in square meters of the heated continuous tube being cooled; Vt is a continuous tube speed in m/s; and DTw is a decrease in temperature of the cooling fluid in a heat exchanger in ° C.

17. A method of cooling a heated continuous tube comprising: providing a cooling tank having an entrance end including an entrance opening, an exit end including an exit opening, said cooling tank having a cooling fluid therein and having a cross section (Sw) of the cooling tank in square meters, said Sw taken in a direction (D) perpendicular to a direction of heated continuous tube movement, relative to the cross section (Ss) in square meters of the continuous tube being cooled is expressed by a relationship:
Sw>37Ss×Vt 33 tstop/Lw wherein Vt is a continuous tube speed in m/s and tstop is a time in seconds of a cessation of cooling in a heat exchanger inserting a first portion of the heated continuous tube into the entrance opening; contacting with a first portion of the cooling fluid in the cooling tank the first portion of the heated continuous tube entering the cooling tank; flowing the first portion of the cooling fluid out the entrance opening; continuously moving the heated continuous tube linearly through the cooling tank; contacting with a second portion of the cooling fluid in the cooling tank a second portion of the heated continuous tube moving through the cooling tank; exiting the cooling tank with at least a partially cooled second portion of the heated continuous tube through the exit opening; and flowing the second portion of the cooling fluid out the exit opening.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is perspective view from above of a quench tank of the present disclosure;

(2) FIG. 2 is a top view of the quench tank of FIG. 1;

(3) FIG. 3 is a front end view of the quench tank of FIG. 1; and

(4) FIG. 4 is a graph of cooling rates as a function of tube wall thickness

(5) Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

(6) “Quenching fluid”, “cooling fluid” and “quenching/cooling fluid” are used interchangeably in this disclosure. It will be understood that a cooling fluid and quenching fluid may be water or other suitable quenching liquid.

(7) It will be understood that cooling is inherently part of the quenching process and as used herein the term “quenching” is broader than and includes the term “cooling” and that the term “cooling tank” is a subset of a “quench tank.”

(8) It will be understood that “s” is used in certain context herein as an abbreviation for the time interval “second” and “mm” is used certain context herein as an abbreviation for the distance measurement “millimeter” and “° C.” is used as abbreviation for degrees Celsius (also sometimes known as degrees Centigrade) and “wt %” is used as an abbreviation for “% by weight”.

(9) It will be understood that as used in this patent application, “CR90” and CR90M″ are interchangeable terms wherein the CR stands for cooling rate and 90 stands for 90% martensite and M stands for martensite. Therefore, CR90 and/or CR90M is the cooling rate (generally provided in degrees C. per second) for a given steel composition to guarantee 90% martenisite in the tube, and wherein CR90 and/or CR90 M is the rate of cooling of the interior surface of the tube when cooling the tube with fluid from the outside surface of the tube.

(10) Referring now to FIG. 1, illustrates a quenching tank system 100 for quenching (e.g. cooling) a continuous tube of a coiled tubing. In general, the quenching tank system 100 includes a cooling tank 160 and in some embodiments a secondary cooling tank 170. Collectors 105 which are used to distribute the quenching/cooling fluid (e.g. water) and to feed eductors 102 are disposed above and in cooling tank 160. The eductors 102 are used to create an overall quenching fluid flow direction F which is opposite to the continuous tube 200 movement direction D through the cooling tank 100. It will be understood that localized turbulence of the cooling fluid and fluid rotation may occur. It will be understood that other means of fluid directors (e.g. nozzles, may be used to create a counter fluid flow in direction F. In addition, the cooling tank 160 includes backing rolls 130 and push rollers 142 for directing and moving the continuous tube from an entrance end 162 of a main cooling tank 160 to an exit end 164 of the quenching tank system 100. The backing rolls are used in order to give support to the continuous tube 200 as it moves through the main cooling tank 160. The push rollers 142 are used to press the tube 200 against the backing roll 130 to assure a straight trajectory. It will be understood that other means may be used to direct and move the continuous tube 200 through the quenching tank system 100 in a straight trajectory and to move the tube 200 through the main cooling tank 160.

(11) The entrance end 162 and exit end 164 of the main cooling tank 160 includes entrance opening 163 to allow for passage of the continuous tube 200 into the main cooling tank 160 and for exit opening 165 to allow passage of the continuous tube out 200 of the tank 160. The openings 163 and 165 also allow for circulation of the quenching/cooling fluid in the quenching tank system 100.

(12) The continuous tube 200 enters continuously through the entrance 162 with minimum bending applied to the tubing. The backing rolls 130 and push rollers 142 apply force to the tube 200 perpendicular to the direction D of tube movement. The push rollers 142 are part of an adjustable push tool apparatus 140 that includes adjustment pistons 144 and 146 that can be used to position the push rollers 142 in contact with different size of diameter continuous tubes 200 being fed through the rolls 142 and 130. The speed and direction D of movement of the tube is controlled by other rollers (not shown) that are positioned outside the main cooling tank 160.

(13) As the heated continuous tube 200 enters the cooling fluid, it begins to cool and gets hard and brittle and hence it is not recommended that the continuous tube be bent during the quenching operation. Bending is not only difficult but dangerous for the integrity of the continuous tube. A desirable feature of this invention is that the continuous tube enters the main cooling tank 160 through entrance opening 163 in the entrance end 162 and exits through exit opening 165 in the exit end 164. The entrance opening 163 and exit opening 165 are aligned with each other in a generally horizontal plane. Therefore, minimum bending is applied to the continuous tube 200 as it moves horizontally and linearly through the main cooling tank 160. This configuration is preferable to a prior art type cooling tank configured with no side openings wherein access to the cooling fluid would necessarily occur by bending the continuous tube downward over the sides of the tank to contact the cooling fluid in the tank. The depth of such a prior art type tank would be related to the angle of impingement with the surface of the cooling fluid, thereby requiring a very large tank for commercial put through rates. This is because the angle of impingement must be minimized to reduce strain in the tube material as it enters a prior art type tank. As the tube enters a prior art type tank the tube will move down in the tank and must be brought back up to exit the tank. Keeping the soft bending of the tube downward and upward during entering and exiting in an acceptable range could only be accomplished in a prior art type cooling tank by using a long tank.

(14) When the heated continuous tube 200 enters the main cooling tank 160 it produces localized heating of a portion of the cooling fluid that is in contact with and near the heated tubing. As the cooling fluid heats up over time due to exposure to the heated tubing, that heated portion of the cooling fluid loses heat extraction capability. If the cooling capacity at the tank entrance is low it may not be possible to achieve the desired CR 90 and other metallic properties. To overcome the loss of heat extraction ability of the heated cooling fluid, the tube must be moved faster and a longer cooling tank may be needed. However such a configuration may result in undesired phase transformations (i.e. the cooling fluid might flash into steam). Hence it is more efficient and hence preferable to bring fresh cooling/quenching fluid to the entrance of the cooling tank where the continuous tube is entering the cooling fluid. In the present invention cooling fluid flows in direction F which is opposite to the direction D of the tubing movement through the tank. Cooling fluid heated by the entering heated continuous tube 200 near the entrance of the continuous tube 200 into the main cooling tank 160 the entrance needs to be evacuated (through the entrance opening 163) and transferred to a heat exchanger and returned to the main cooling tank 160 through the educators 102 in a continuous circulation process.

(15) Heat extraction at the surface of the tubing is associated with the heat transfer conditions. Maximum heat transfer is achieved by the relative movement of the tubing in direction D counter to the cooling fluid flow direction F. In some implementations, water is provided to the main cooling tank 160 through eductors 102 positioned and configured to produce high turbulence in the cooling tank and provide continuous overflow of the cooling fluid from the tank to a collection channel(s) and/or drains outside the tank.

(16) Experimental Data

(17) Test data indicates that the quenching of a medium carbon steel with and without eductors results in a variation in the amount of martensite in the microstructure from 90% down to 78% as shown in the table below. Considering experimental error, 86% is satisfactory and is near the design target of 90%. Hardness is related to the content of martensite which is a hard constituent of the microstructure of the tube. So hardness and martensite content are both evidence of a better quenching result

(18) TABLE-US-00002 Trial QT3 QT4 Eductors No Yes Avg. HRC 46.0 47.0 Std. Dv. HRC 1.8 1.2 Max. HRC 48.2 49.3 Min. HRC 39.8 43.5 Avg. HV 459 473 M fraction 78% 86%

(19) The hardness is measured using the Rockwell scale (HRC) and with the Vickers Pyramid number (HV), according to the table above we can see that the hardness is improved by the use of eductors. The Martensite fraction is also improved by the use of eductors. Hardness is related to the content of martensite which is a hard constituent of the microstructure. So both hardness and martensite content are both evidence of a better quenching. The criticality for the control of fluid flow increases as the pipe is bigger and thicker, or the chemistry hardenability decreases.

(20) The time of the main cooling is related to the productivity of the line (linear velocity) and the dimensions of the pipe. Calculations for different products were estimated.

(21) TABLE-US-00003 Quenching Tank Tube Time Pipe Pipe Linear HT Expected (1050° C.- OD WT Weight Speed productivity 120° C.) Length In In lbs/ft fpm Ston/h s m 1.000 0.109 1.04 68 2.12 7.8 2.69 1.250 0.175 2.01 68 4.11 12.9 4.45 1.500 0.204 2.83 72 6.11 17.3 6.33 1.750 0.250 4.01 72 8.67 21.6 7.91 2.000 0.280 5.16 72 11.14 24.6 9.00 2.375 0.300 6.66 60 12.00 26.9 8.20 2.625 0.300 7.47 52 11.65 27.3 7.21 2.875 0.190 5.46 68 11.14 17.3 5.97 OD: Outside Diameter WT: Wall thickness HT: Heat treatment

(22) OD: Outside Diameter

(23) WT: Wall thickness

(24) HT: Heat treatment

(25) During the quenching process the temperature of the cooling fluid increases because of the heat released by the pipe (which is cooled from austenitization temperature down to about 150° C.). When water is used for the cooling fluid, the maximum working temperature of the water in the main cooling tank pool is 60° C. At higher temperatures the heat extraction from the tube to the quenching media (e.g. water) is too low to reach critical cooling rates needed to form at least 90% martensite. In order to avoid excessive heating of the quenching fluid, it is recirculated in a closed loop through a cooling facility (for example a cooling tower). The quenching-fluid flow rate (Qw) in m.sup.3/s in the circuit formed by the main tank and the cooling facility should be:
Qw>1000×Ss×Vt/DTw
where Ss is the cross section in square meters of the pipe being cooled, Vt is the tube speed in m/s and DTw is the quenching-fluid temperature-drop in the cooling facility (for example in the cooling tower) in ° C.

(26) The cross section of the main cooling tank Sw (area measured in square meters in the direction perpendicular to that of the pipe movement) has to be large enough to avoid excessive heating of the quenching fluid due to an unexpected stop of the cooling facility. Sw depends on the average time needed to resume the cooling facility operation (tstop) in the following way:
Sw>37×Ss×Vt×tstop/Lw
where Lw is the length of the cooling tank in meters in the direction of pipe movement, tstop is in seconds, and the other parameters were previously defined. For example, if it is needed to allow for a 1200 seconds stop of the cooling facility without affecting the quenching process, the minimum cross section Sw should be 1.69 m.sup.2 when Ss is 9.76E-4 m.sup.2 (pipe with OD 2 inches and WT 0.28 inches), Vt is 0.36 m/s (72fpm) and Lw is 9 m.

(27) Water flow in the pool and line speed have to be selected in order to guarantee a minimum relative velocity (Vmin) between the pipe and the quenching media. Otherwise the heat extraction during quenching is not enough to reach the critical cooling rate (CR90 M) necessary to form at least 90% martensite. The minimum relative velocity of the tube as it moves through the main cooling tank depends on pipe wall thickness (WT) and critical cooling rate (CR90M) necessary to form 90% martensitic in the following way:
Vmin>1/100+1/145×(WT−2.77)+1/1500×(CR90M−20)
where Vmin is in m/s, WT is in mm and CR90M is in ° C./s. The CR90M is the cooling rate of the interior surface of the tube when cooling the tube from the outside surface of the tube. The expression is valid for WT=2.77-7.62 mm, CR90M=20 to 50° C,/s and water temperature up to 35° C.

(28) For water temperature up to 60° C. the following expression is valid for the same WT and CR90M ranges previously stated (larger Vmin than in previous case are needed to compensate for the reduction in the heat extraction coefficients due to the higher cooling media temperature):
Vmin>1/20+1/45×(WT−2.77)+1/300×(CR90M−20)

(29) A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.