Automated Hot Wire TIG with Positioner for High Productivity Quality Welding

Automated hot wire TIG with positioner for high productivity quality welding

Veris, Inc., a manufacturer of flow sensors in Niwot, Colorado, is using the automated hot wire GTA welding process to weld advanced technology differential pressure flow sensors. The company planned its welding system applications in collaboration with Arc Machines Custom Engineering to produce very high quality, high production welds of corrosion resistant materials. The equipment, which has proven to be very durable, functions in a “dirty” environment from an electronic point of view with hardly any down time in 5 years of operation. Hot wire TIG is an under-utilized technology that can pay big dividends in the right application and could be much more widely used in the nuclear and other industries requiring high quality, high productivity welding.

By Barbara K. Henon, Ph.D. Arc Machines, Inc.


Hot wire TIG welding set-up at Veris Inc. The Model 415 GTAW Power Supply/Controller
and Model 501 Hot Wire Power Supply and a Pandjiris Rotating Positioner are from Arc Machines, Inc.

Model 415 Power  Supply/Controller stores
weld programs and controls Model 501 Hot Wire Power Supply and Pandjiris  Positioner.

Weld on joint between flange and body. Unit is turned by a rotating positioner while the
Model 2 torch remains stationary (except for oscillation). The green hose delivers the ID purge of inert argon gas.

The addition of the second Pandjiris Rotary Positioner has dramatically increased productivity by performing welds at the second location while welds at the first location cool to interpass temperature.
 
 
In preparation for welding, an insert ring is precision tack welded in place to the flange.
The flange is mounted on a precision frame which provides identical accurate alignment
of each weld joint.

 


 

In 2007 Veris, Inc. won an Innovation Award for the year’s most compelling fluid handling technologies for their Extended Range Accelabar® Flowmeter. This innovative flowmeter combines two flow measurement technologies in a singlemeter. The Accelabar nozzle has a patented straight-run settling distance that accelerates, linearizes, and stabilizes the velocity profile. A Veris Verabar® averaging pitot tube located within the nozzle accurately measures and significantly increases the differential output to extend the operating range (turndown). Prior to the development of the Accelabar, flowmeters required long lengths of straight pipe while the Accelabar requires zero.

Older type systems could not handle the total flow rate range with a single meter. Thus, the combination of the two technologies, an averaging pitot tube within the special flow conditioning nozzle, produces higher accuracy over an extended turndown with no straight run requirements. The system can be flexible if sized for changes in future flow capacities, for example, by installing a six inch meter in a four inch pipe.

There are many applications for this technology. For example, it has enabled the University of Georgia to install flowmeters in steam piping that was not designed for flow meters and where there was no space to incorporate additional lengths of piping that would be required for conventional flowmeters. Another industrial application was to verify the accuracy of a custody-transfer turbine meter monitoring a propylene supply line in a large chemical plant. The Accelabar was installed between an upstream valve and a downstream tee where there was no straight run other than that built into the flowmeter.

The flowmeter can be equipped with aspecial mounting plate that allows two differential pressure (DP) transmitters to be directly mounted to the meter. Temperature sensors may be installed in the thermowell and connected to a transmitter. For steam applications, density can be calculated from temperature and pressure measurements.This advanced flowmeter technology has been used extensively in the natural gas industry providing flow measurement in all phases of operation from the producer to the consumer. The ability to provide accurate measurements at extremes of high and low flow rates has significantly translated into improved material accountability and lower operating costs with increased profitability for the customers.

Choice of welding process

Veris, which has been at their present site since 1997, initially used manual welding to manufacture their products, but they soon recognized the need for higher productivity and quality. They anticipated a large and growing demand for their new Accelabar product and wanted to plan for high production welding.

The weld joints are between a central casting containing the sensor with flanges on either side that connect with piping. The number of weld joints per unit varies from2 to 4 depending on whether reducers or other components are used.

The joint sizes range between 2 inch and 14 inches schedule 80 pipe. A variety of different materials including carbon steel, stainless steel, duplex stainless steel, chrome moly, and various nickel-based alloys are used depending on the corrosion requirements of the customer’s application. Typically, the type of weld joint on this assembly, 37 1/2 degree angle with a 0.060inch weld land, would be done with the MIG process because of the high rate of deposition. However, the MIG process does not provide the quality of welding that was desired for this product. Although the GTAW, or TIG process has a much lower deposition rate than MIG, the quality is generally superior. With the addition of Hot Wire technology, at least on the larger sizes, deposition rates can approach that of MIG while realizing GTAW quality.One reason for the need for quality is that the corrosion resistant materials used in manufacturing the sensors are costly, and aweld reject would significantly increase the cost of production. Because of the demand for high quality and the use of corrosion resistant materials, Veris Engineering Manager, Pat Kemp, selected the GTAW welding process. Pat was familiar with the Arc Machines Model 81 pipe weld headused by his previous employer and contacted Arc Machines, Inc.. Arc Machines is predominant in orbital GTA welding, but they had already configured several downhand welding systems for a nuclear component application using a Model 415 GTAW Power Supply/ Controllerand a Model 501 Hot Wire Power Supply, with a Model 2 Weld Head mated to a Pandjiris Positioner for the weld rotation. A similar system was developed for Veris and they purchased and installed the equipment in January, 2005.

Welding set up

The Arc Machines Model 415 is designed to be a versatile welding automation controland power supply system. The basic Model 415 includes a complete complement of welding controls, as well as water cooling and gas control. The Model 415 is a programmable Windows®- based powersupply/controller that provides up to 400 amps of welding current. The machine is easy to operate and almost all of its function ranges and modes can be defined by the user to exactly match the welding head or fixture being used. While most applications of the Model 415 involve the use of AMI orbital weld heads, additional optional closed-loop motor servos and/or open loop motor manipulator controls make it ideal for work cell manufacturing environments or for use with custom welding heads having unique functions. The Arc Machines Model 2 is a series of specialized durable, high precision components that are custom configured for a specific set of application requirements.

The Model 2uses a series of standardized motionstages for functions such as AVC (ArcVoltage Control, Torch Oscillation (weaving)together with onboard wire feeder andtravel, and several varieties of torches.

In the flowmeter application, the 415 Power Supply/Controller is the “brains” of the operation used to turn on and control the Pandjiris rotary positioner as well as the Model 501 hot wire power supply. Thepositioner rotates at a speed determined by the weld program that resides in the memory of the Model 415. The wire spool and torch assembly are mounted on a beam that positions the Model 2 system horizontally. Coarse movements of the Model 2 torch for location along the side beams are controlled by the positioner, (ormanually) while precision oscillation and arc gap (AVC) are controlled by the Model 415 power supply. The precision AVC motion is realized on the Model 2 vertical slide, while weaving motions are realized on the horizontal slide. Welding parameters include primary and background amps, rotation speed, pulse times, wire feed OFF/ON, wire feed speed, dwell, etc. The weld sequence is initiated by the welding operator from the remote operator pendant. The operator views the weld through the patented Heads Up Display® and can make minor adjustments to weld parameters during the weld.

Hot wire The key feature of the Arc Machines, Inc. Model 501 Hot Wire TIG (GTAW) Power Supply is the accuracy and repeatability of the wire heating. The wire is fed through a hot wire nozzle mounted on the Model 2 torch that heats the wire to near melting temperature as the wire enters the weld pool. Wire feed is initiated by the Model 415 which turns on the Model 501. The hot wire guide tube is aimed at the trailing edge of the weld puddle with a wire entry angle of 45 to 50 degrees which is typically steeper than is common with cold wire. Some trial and error is required to properly adjust the hot wire voltage setting and to establish a working wire feed speed. Four days of operator training and equipment installation was done by an Arc Machines, Inc. factory instructor. The Veris welding operator, Daniel Hemker, has been a welder for 30 years and has become adept at monitoring the welds and assuring complete penetration of each joint. Software for this application was developed by Arc Machines, Inc.

Hot wire efficiency relative to pipesize

The efficiency of hot wire TIG is highly dependant on the pipe diameter. The hotwire is not used on 2 inch pipe as this size is too small to benefit from the process.The travel speed is held constant between 2 and 2 - 1/2 inches per minute (IPM) on all pipe sizes. The hot wire is turned off for the root pass as a consumable insert ring of appropriate chemistry serves as filler. On as maller diameter pipe, the the hot wire feed can be in the range of 90 IPM, while on a 12 inch pipe the wire feed speed can be 160 to 170 IPM approaching MIG deposition rates with TIG quality.

Addition of second positioner and beam Recently, Veris added a second rotary positioner which has nearly doubled their productivity as this allows welding at the second location while the weld at the first location cools to interpass temperature. Fora 3 inch diameter weld joint, the first pass takes 5 minutes followed by cooling time, then another 5 minute pass. Veris says that work taking a week to complete manually without hot wire can be done in a single day when hot wire is used. A total of 8,300 welds have been completed over four years. Expecting over 4,000 welds for 2010, Veris is looking atadding another setup to meet the demand. The success rate of welds in this system has been amazing with only two weld rejections during the four years of operation.

Conclusions

The welding system which Veris developed in collaboration with Arc Machines Custom Engineering produces very high quality, high production welds of corrosion resistant materials. The versatile system is easily adapted to a complete range of pipe diameters and lengths. The equipment, which has proven to be very durable, functions in a “dirty” environment from an electronic point of view with hardly any down time in 5 years of operation. They trained their people and developed a precision weld joint which facilitates weld repeatability. The welding system has more than paid for itself. Hot wire TIG is an under-utilized technology that can pay big dividends in the right application such as the Accelabar production. It could be much more widely used in the nuclear and other industries requiring high quality, high productivity welding.

Photos by Richard Shilling, President RC International, LLC.