DESC:AUTOMATED SYSTEM FOR OVERLAY WELDING AND METHOD THEREOF
Field of the invention:
The present invention generally relates to a system and method for weld overlay and more particularly it relates to an automated system and method for bulge overlay application.
Background of the invention:
Coke drums are an essential component in the delayed coking process (DCU) in petroleum refineries. Coke drums are vertical pressure vessels used to separate petroleum coke from lighter hydrocarbons. Because the drums are central to the coking process, poor drum reliability can lead to frequent shutdowns and low productivity. To achieve higher throughputs, the coke drum undergoes shorter and more frequent cycles. As a result of this, the most common defect observed in the coke drum is bulging which is a non-uniform radial growth in a shell. Bulging often leads to cracks that result in leaks and fires. Weld overlay is a repair method that has been used over the last few years to limit the growth of bulges and to extend the remaining life of delayed coking drums. Different refinery operators use varied approaches, ranging from localized patches on specific regions of concern, to bands along circumferential welds, to large sections of structural repair that completely cover a bulged area. As per recommendations of API TR 934-G standard, to extend the life of the coke drum, and also to ensure safe and reliable operation, the bulge area needs to be reinforced with Inconel 625 overlay after removal and repair of cracks if any. The volumetric quality of the deposit and the careful control of welding parameters are critical to the success of the weld overlay execution, necessitating the need for weld automation.
In case of manual welding, for such huge overlay deposition it requires high labor strength and it also leads to poor quality due to human error. But if it is executed automatically, the quality and productivity can be improved. Furthermore, better features of surface finish can also be achieved with smallest dilution rate of added material. The automation of weld overlaying for huge dimensions and non-uniform bulge constitutes a major challenge.
Accordingly, there exists a need to provide an automated system and method for bulge overlay application to provide weld overlay of consistent quality to overcome the drawbacks in the prior art.
Objects of the invention:
An object of the present invention is to provide consistent quality weld overlay for coke drums used in the delayed coking process.
Another object of the present invention is to deploy continuous welding technique using Programmable Logic control
Still another object of the present invention is to ensure smooth and reliable weld deposit on bulges using auto Arc Current Control sensors.
Yet another object of the present invention is to maintain constant stick out during welding.
Summary of the invention
Accordingly, in one aspect, the present invention provides an automated system for bulge overlay welding. The bulge overlay welding system comprises of a welding unit, a welding power source, a human machine interface and a control unit. The welding unit includes a welding carriage having a vertical slide, an arc current control (ACC) slide and a welding torch are mounted thereon. The welding power source providing current for welding is fitted with a sensor for monitoring the welding current, wherein the lower limit and the upper limit of the welding current are calculated using defined ACC current and ACC band. In an embodiment, the sensor for monitoring the welding current is a Hall Effect sensor. The human machine interface is provided with a communication port and a graphical interface for receiving welding parameters as input, wherein the human machine interface is a programmable pendant operably connected to the welding unit and to the control unit either in wired manner or in wireless manner. In an embodiment, the welding parameters include but not limited to travel speed of welding carriage, vertical offset of vertical slide after each pass, direction movement of the vertical slide and welding carriage, sampling time and correction speed in arc current control module, welding carriage axis delay after each start, travel speed of vertical slide after each pass, and upper and lower limit of welding current and arc voltage analog signals. The control unit is operably connected to the human machine interface and to the welding unit, wherein the control unit executes welding process through the welding unit as per the welding parameters received from the human machine interface. The control unit includes a welding control module for enabling and controlling ON/OFF function of the welding unit, a stepper motor control module for enabling and controlling movement of the welding carriage, the vertical slide, the weaving slide, and the ACC slide within predefined start and end point; and an arc current control module for enabling and controlling in and out movement of the welding torch depending upon the average welding current. A constant stick out is maintained during welding by the ACC module by moving the welding torch depending upon the average welding current. The welding torch is moved in when the average welding current is less than the lower current limit and the welding torch is moved out when the average welding current exceeds the upper current limit.
In another aspect the present invention provides method for carrying out overlay welding on a bulged patch of a coke drum. In the method, the start points and end points for weld overlay of the bulged patch on horizontal axis and the welding parameters are defined using the human machine interface and communicated to the welding control unit. An ACC enable value, ACC Current and ACC Band are also defined to calculate an upper current limit and a lower current limit of a welding current, wherein the welding current is monitored by a sensor mounted in a welding power source. A dry run is carried out with predefined welding parameters by the control unit to insure proper working of the system. The welding control module and the stepper motor control module are activated by the control unit, respectively for controlling the ON/OFF function of the welding unit and for controlling the movement of the welding carriage, the welding torch, the vertical slide, the weaving slide, and an ACC slide within the predefined start and end points. In next step, the arc current control module is activated by the control unit when the welding current value exceeds a predefined ACC enable value, wherein a constant stick out is maintained by the arc current control module by moving out the welding torch when the welding current exceeds the upper current limit value and moving in the welding torch when the welding current is less than the lower current limit value.
Brief description of the drawings:
The objects and advantages of the present invention will become apparent when the disclosure is read in conjunction with the following figures, wherein
Figure 1 shows schematic diagram of an automated system for overlay welding, in accordance with the present invention;
Figure 2 shows schematic diagram of the automated system for overlay welding, in accordance with the present invention;
Figure 3 shows process flowchart of the automated system for overlay welding, in accordance with the present invention; and
Figure 4 shows operation flowchart of an ACC module of automated system for overlay welding, in accordance with the present invention; and
Detailed description of the embodiments:
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments.
The present invention provides an automated system and method for overlay welding for extending the life of coke drums. The system consists of a welding unit, a welding power source, a human-machine interface unit and a PLC control unit operably connected to each other. There are several welding processes such as SMAW, GMAW, GTAW, FCAW etc which can be used for overlay welding. Nowadays, due to the easy automation, high productivity, flexibility (working for most welding position and material), low heat input, and high deposition rate, Pulsed Gas Metal Arc Welding is the most used technique in the industry for weld overlay. It can also be designed to work in harsh environment with minimal maintenance intervention. Hence Pulsed GMAW is selected for Bulge overlay application. Pulsed GMAW is modified spray transfer mode in which current is varied between peak and background current with rate about 70-150 Hz. It uses a continuous feed of a consumable wire electrode that is fed directly into the weld pool to form the weld bead. The system of present invention is easy to set up by the operator and suitable for harsh environment.
Another challenge with the repair welding of aged and in-service pressure equipment is to carry out the task with minimum disruption to the operation. The present invention facilitates deploying the temper bead technique thereby eliminating the requirements for post weld heat treatment (PWHT). In temper bead welding technique, the HAZ of the barrier layer against base metal is tempered by a subsequent layer with higher heat input.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description and in the table below.
Table:
Ref No: Component Ref No: Component
2-2 CT cable 42 Weaving slide
4-4 Communication cable 44 ACC slide
6 Current cable 50 Arc current control unit
8 Power plug 52 Control box
10 Control unit 54 ACC Cable
12 Stepper motor control module 56 Wire feeder
14 Arc current control module 57 Welding spool holder
16 Welding control module 58 Gas ON indicator
20 Human-Machine Interface 60 Welding carriage
30 Welding power source 62 Trolley drive (motor/gear box)
40 Welding Torch 64 Vertical slide
Referring to the figures 1 to 4, an automated system (100) and method for overlay welding (hereinafter referred to as “the system (100)”) in accordance with the present invention is shown. The system (100) comprises of a welding unit (not numbered), a welding power source (30), a human-machine interface unit (20) and a control unit (10) operably connected to each other.
The welding unit includes a welding carriage (60), a control box (52), a wire feeder (56), a welding spool holder (57), and a trolley drive (motor/gear box) (62). A vertical slide (64), a weaving slide (42), an ACC slide (44) and a welding torch (40) are mounted on the welding carriage (60). The welding carriage (60) is suitable for aluminium rigid guide track of any diameter above 3m. A toggle clamping system is provided to load the vertical slide (64) onto the welding carriage (60). This provides an easy to do set up for a single operator. The welding carriage (60) can be used for overlay over patch of length 5 m and height 1.5 m in single set-up. The welding torch (40) is an air cooled welding torch provided with a separate liner, current cable, and gas supply hose.
The welding power source (30) provides current for welding. The welding power source (30) is a fully digitized and microprocessor-controlled synergic power source suitable for metal inert gas (MIG) welding, metal active gas (MAG) welding, Tungsten inert gas (TIG) welding and manual metal arc (MMA) welding. The welding power source (30) of any make can be integrated with the system (100). The welding power source (30) offers a synergic database in which synergic line is provided for different materials with different wire diameters and modes (Pulsed, Standard, and Manual). Welding parameters such as wire feed rate, ALC (Arc Length Correction), PCF (Pulsing Correction Factor) are stored as job number. So that it can easily be called through PLC instead manual setting. Pulsed GMAW is modified spray transfer mode in which current is varied between peak and background current with rate about 70-150 Hz. With the help of pulsed mode, higher deposition is achieved with less heat input and least spatter compared with manual mode (Constant Voltage).
The welding power source (30) is provided with a sensor (not shown) for monitoring the welding current. In an embodiment, the sensor is a Hall Effect sensor mounted in the welding power source (30) for monitoring the welding current (I). The welding current is used as input for maintaining constant stickout during overlay welding over the bulged surface. The stick-out refers to the length of the welding wire that extends outside the contact tube. The correct and constant wire stick-out is important to ensure that the weld has the proper penetration. The lower current limit and the upper current limit of the welding current are calculated using defined ACC current and ACC band. Welding current value changes with a change in the stickout, which is sensed by the sensor.
The human-machine interface unit (20) is provided with a communication port and a graphical interface, and operably connected with the control unit (10) in wired or wireless manner to accomplish the input and display of welding parameters. The human machine interface (20) is used to monitor and control all the parameters including but not limited to welding mode, travel direction, travel distance, welding travel speed, vertical offset after each pass, weaving speed, oscillation dwell time, carriage stroke, ACC current, ACC current band, weaving width, weaving speed, the on-delay timers of arc, carriage trolley motion, and arc current control, sampling time, correction speed for ACC module and like. The welding mode can be selected from Manual/Auto, Dry/Arc-On, Weaving/Without weaving, etc. Using the human-machine interface unit (20), the user can select the job number that stores welding parameters such as wire feed rate, ALC (Arc Length Correction), PCF (Pulsing Correction Factor). In an embodiment, the human-machine interface unit (20) is a programmable pendant for operating the system (100).
The control unit (10) is operably connected to the human machine interface (20) and to the welding unit. The control unit (10) is a PLC controlled unit that executes welding process through the welding unit as per the welding parameters/job numbers received from the human machine interface (20). The control unit (10) includes a stepper motor control module (12) (hereinafter referred as “the SMC module (12)”), an arc current control module (14) (hereinafter referred as “the ACC module (14)”) and a welding control module (16). The welding control module (16) controls ON/OFF function of the welding unit; the SMC module (12) controls movement of the welding carriage (60), the vertical slide (64), the weaving slide (42), and the ACC slide (44) within predefined start and end point; and the arc current control module (14) controls in and out movement of the welding torch (40). To maintain the constant stick out, the welding torch (40) is moved in by the arc current control module (14), when the average welding current is less than the lower current limit and the welding torch (40) is moved out by the arc current control module (14) when the average welding current exceeds the upper limit.
Referring to figure 2, the welding carriage (60) is capable of moving along Axis 1 in horizontal direction and the vertical slide (64) is capable of moving along Axis 2 in vertical direction. The movement of the welding torch (40) is controlled by the ACC module (14) depending upon the welding current, to maintain constant stick-out along the bulged surface. The welding torch (40) is oscillated in the direction of welding to achieve low dilution and better surface finish. This is achieved by moving the weaving slide (42) along Axis 3 and moving the ACC slide (44) along Axis 4.
Referring to figure 3, process flowchart of the system (100) is shown. For carrying out overlay welding on a bulged patch, start points and end points for weld overlay of the bulged patch are defined on horizontal axis (Axis 1). The welding parameters such as wire feed rate, ALC (Arc Length Correction), PCF (Pulsing Correction Factor) are stored in welding powers source as job number. The job numbers, other welding parameters, start points and end points for weld overlay of the bulged patch are fed into the human machine interface (20) and communicated to the control unit (10). The control unit (10) receives input from HMI (20) to process, analyze and send command to the welding power source (30) and welding carriage (60). The welding parameters include but not limited to:
? the travel speed of welding carriage (60);
? vertical offset after each pass;
? direction of up and down movement of the vertical slide (64) and direction of left and right movement of the welding carriage (60);
? sampling time and correction speed in ACC unit (14);
? control speed of manual mode axis 1, 2, 3 and 4;
? welding carriage axis delay after each start;
? travel speed of vertical slide (64) after each pass;
? lower limit (Lower set value, LSV) and upper limit (upper set value, USV) of welding current and arc voltage analog signal;
? welding current value for enabling ACC module (14);
? weaving width, Auto/Manual Mode, Dry/ Weld on Mode, and
? weaving ON/OFF.
The system (100) is operable in any of the Auto and manual mode. In auto mode, the movement of the welding carriage (60), the vertical slide (64), the weaving slide (42) and the ACC slide (44) along the horizontal and the vertical axis is carried out automatically by the control unit (10) as per the program installed in the system (100), while in manual mode the movement of the welding carriage (60), vertical slide, the weaving slide (42) and the ACC slide (44) is controlled during set up prior to start of actual welding.
Before starting the actual welding process, welding operator can ensure working of system in dry run mode. Emergency button is provided to stop operation immediately in case any malfunction ensuring safety.
In auto and arc-on mode, after axis delay time, welding is ON and the welding carriage (60) starts from the defined start point (position 1) and moves along Axis 1 in predefined direction with predefined travel speed. Once the welding carriage (60) reaches the defined end point (position 2) the welding is OFF and the vertical slide (64) travels by vertical offset distance along the Axis 2 with predefined vertical slide travel speed. After vertical offset, the vertical slide (64) stops and starts cycle again in opposite direction along Axis 1 with welding ON and continues with predefined travel speed.
In Weaving ON mode, the welding torch (40) oscillates along Axis 3 with defined weaving width and weaving speed.
The ACC module (14) is activated when the welding current value exceeds ACC enable value. The ACC module (14) enables in and out movement of the welding torch (40) along the Axis 4, for maintaining the constant stick-out during welding.
Referring to figure 4, an average welding current is measured for a defined sampling time. When the average welding current exceeds the upper current limit, the welding torch (40) is moved out by the ACC module (14) with correction speed and when the average welding current is less than the lower current limit, the welding torch (40) is moved in by the ACC module (14) with correction speed to maintain constant stickout.
The method of overlay welding of the present invention is further illustrated by the following example. The example is given by way of illustration and should not be construed to limit the scope of present invention.
Welding Procedure Qualification for Bulge Overlay Repair using Inconel Overlay
For procedure qualification, the base metal used is LAS SA 387 GR 11 CL2 and thickness is 40mm. Inconel 625 overlay is carried out by ERNiCrMo-3 filler wire using Automatic GMAW overlay system using TBW. Shielding gas used is Argon (99.997%). Initially, weld deposition against base metal is done by preheating base metal to 1000C in horizontal position. It is followed by subsequent layer by increasing heat input from 0.47 kJ/mm in barrier layer to 0.63 kJ/mm. The ratio of heat input in subsequent layer to barrier layer is 1.34. Welding parameters used are shown in table 2 below:
Table 2
Welding Parameter Barrier Layer Subsequent Layer
Electrode diameter (mm) 1.2 1.2
Welding Current (A) 195-205 225-235
Voltage (V) 23-25 24-27
Travel Speed (mm/min) 650 600
Electrode stick out (mm) 15-20 15-20
Gas Flow rate (lpm) 20-25 20-25
Overlap 50% 50%
Mode of Metal Transfer Pulsed Spray Pulsed Spray
Weld Metal Thickness 4-4.5 mm 5.5-6 mm
Base Metal Carbon Equivalent (CE): 0.65
After overlay, plate is subjected to ultrasonic examination wherein no unsound region was noticed.
For the evaluation of mechanical properties, bending and hardness tests were performed, as required by the procedures used for qualification. Also, four guided side-bend tests with angle of bend 180° were performed at room temperature on test specimens removed transversely to the weld deposits, in accordance with ASME IX (QW 451). Vickers hardness measurements with a 10 kg load were taken across the weld metal, heat affected zone, and base metal with permissible location and orientation of hardness traverses suggested in QW-462.12 of ASME Sec IX.
Using temper bead welding method, average value of hardness in HAZ achieved is less than 287 VHN that met customer requirements.
Chemical analysis was carried on weld metal at different positions from the fusion line, by means of optical emission spectroscopy using ASTM E-3047-16 Method. The undiluted chemistry is met at distance of 3 mm from fusion line.
Advantages of the invention:
• The system (100) is technologically superior which helps in achieving the required mechanical and metallurgical properties stipulated as per codes, standards and project specification
• The system (100) performs welding with a fully automatic pulsed GMAW process intruder to achieve superior quality welds
• The system (100) facilitates deploying the temper bead technique thereby eliminating the requirements for post weld heat treatment (PWHT)
• In temper bead welding technique, the HAZ of the barrier layer against base metal is tempered by a subsequent layer with 25-35% higher heat input.
• The system (100) can be used for overlay over area with bulges about 200 mm in single set up.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the claims of the present invention.

,CLAIMS:We claim
1. An automated system (100) for bulge overlay welding, the system (100) comprising:
a welding unit including a welding carriage (60) having a vertical slide (64), a weaving slide (42), an ACC slide (44) and a welding torch (40) mounted on the welding carriage (60);
a welding power source (30) providing current for welding, the welding power source (30) provided with a sensor for monitoring the welding current, wherein the lower limit and the upper limit of the welding current are calculated using defined ACC current and ACC band;
a human machine interface (20) provided with a communication port and a graphical interface for receiving welding parameters as input; and
a control unit (10) operably connected to the human machine interface (20) and to the welding unit, wherein the control unit (10) executes welding process through the welding unit as per the welding parameters received from the human machine interface (20), the control unit (10) including:
a welding control module (16) for enabling and controlling ON/OFF function of the welding unit;
a stepper motor control module (12) for enabling and controlling movement of the welding carriage (60), the vertical slide (64), the weaving slide (42), and the ACC slide (44) within predefined start and end point; and
an arc current control module (14) for enabling and controlling in and out movement of the welding torch (40) depending upon the average welding current, wherein to maintain constant stick out during welding, the welding torch (40) is moved in when the average welding current is less than the lower current limit and the welding torch (40) is moved out when the average welding current exceeds the upper current limit.
2. The automated system (100) for bulge overlay welding as claimed in claim 1, wherein the human-machine interface (20) is a programmable pendant operably connected to the welding unit and to the control unit (10) either in wired manner or in wireless manner.
3. The automated system (100) for bulge overlay welding as claimed in claim 1, wherein the sensor for monitoring the welding current is a Hall Effect sensor.
4. The automated system (100) for bulge overlay welding as claimed in claim 1, wherein the welding parameters include but not limited a travel speed of welding carriage (60), vertical offset after each pass, direction of up and down movement of the vertical slide (64) and direction of left and right movement of the welding carriage (60), sampling time and correction speed in ACC unit (14), welding carriage axis delay after each start, travel speed of vertical slide (64) after each pass, lower limit value and upper limit value of welding current and arc voltage, welding current value for enabling ACC module (14), weaving width, Auto/Manual Mode, Dry/ Weld on Mode, and weaving ON/OFF.
5. The automated system (100) for bulge overlay welding as claimed in claim 1, wherein the welding torch (40) is an air cooled welding torch provided with a separate liner, current cable, and gas supply hose.
6. A method for carrying out overlay welding on a bulged patch, the method comprising the steps of:
defining start points and end points for weld overlay of the bulged patch on horizontal axis and defining welding parameters for weld overlay of the bulged patch in a human machine interface (20);
communicating the welding parameters and the start and end points for weld overlay of the bulged patch to a control unit (10);
defining ACC enable value, ACC Current and ACC Band to calculate an upper current limit and a lower current limit of a welding current, wherein the welding current is monitored by a sensor mounted in a welding power source (30);
carrying out a dry run with predefined welding parameters by the control unit (10) to insure proper working of the system;
activating a welding control module (16) and a stepper motor control module (12) by the control unit (10), wherein the welding control module (16) controls the ON/OFF function of the welding unit and the stepper motor control module (12) controls movement of a welding carriage (60), a welding torch (40), a vertical slide (64), a weaving slide (42), and an ACC slide (44) within the predefined start and end points;
activating an arc current control module (14) by the control unit (10) when the welding current value exceeds a predefined ACC enable value, wherein a constant stick out is maintained by the arc current control module (14) by moving out the welding torch (40), when the welding current exceeds the upper current limit value and moving in the welding torch (40) when the welding current is less than the lower current limit value.
7. The method for carrying out overlay welding on a bulged patch as claimed in claim 6, wherein the welding parameters include but not limited to a travel speed of welding carriage (60), vertical offset after each pass, direction of up and down movement of the vertical slide (64) and direction of left and right movement of the welding carriage (60), sampling time and correction speed in ACC unit (14), welding carriage axis delay after each start, travel speed of vertical slide (64) after each pass, lower limit value and upper limit value of welding current and arc voltage, welding current value for enabling ACC module (14), weaving width, Auto/Manual Mode, Dry/ Weld on Mode, and weaving ON/OFF.
8. The method for carrying out overlay welding on a bulged patch as claimed in claim 6, wherein the SMC module (12) is activated after axis delay time, the ACC module (14) is activated after ACC delay time and the welding control module (16) is activated after weld on delay time in auto and arc-on mode.
9. The method for carrying out overlay welding on a bulged patch as claimed in claim 6, wherein the human-machine interface (20) is a programmable pendant operably connected to the welding unit and to the control unit (10) either in wired manner or in wireless manner.
10. The method for carrying out overlay welding on a bulged patch as claimed in claim 6, wherein the sensor for monitoring the welding current is a Hall effect sensor.
11. The method for carrying out overlay welding on a bulged patch as claimed in claim 6, wherein welding torch (40) is an air cooled welding torch provided with a separate liner, current cable, and gas supply hose.
Dated this on 19th day of October, 2022

Ashwini Kelkar
(Agent for the applicant)
(IN/PA-2461)