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Enhanced Surface Tension Transfer for Pipe Welding
Harry Sadler
Manager Military and Shipbuilding Sales
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Conventional Short Circuit Transfer
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Traditional Short Circuit Transfer
click on picture to run video
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STT Process
Research Began
July,1985
• Purpose
– Develop a semi - automatic “short
circuiting” welding process which
eliminates spatter when using 100%
CO2 shielding gas.
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STT Process
Working Prototype
January,1987
• Major Achievements
– Reduced spatter in 100% CO2
– Developed capability to use larger
diameter electrodes
– Reduced fumes
– Ability to control the welding current
independent of the wire feed speed.
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STT Process
Working Prototype
January,1987
• Results
– The spatter reduction feature of the
technology also produced a very stable
arc, especially at low currents. This is a
big advantage when welding the open
root on pipe in the 5G position
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STT Process
STT Welding Arc
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STT Process
• Background current
– Arc current level prior to shorting to the weld
pool.
– Contributes to the overall heat input
– Keeps arc lit
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STT Process
• Initial Shorting
– Response to the “arc voltage” detector
sensing that the arc has shorted
– Current is reduced even further at
actual ball/weld puddle contact
– Extremely low current promotes ball
wetting instead of repelling
– Reason for lower spatter in STT
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STT Process
• Pinch Current
– High current is applied immediately after the
initial short
– Current increases, causing the molten droplet to
separate from the electrode
– STT electronically calculates when droplet
separation is to occur and reduces the current
before this happens, eliminating the explosive
spatter.
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STT Process
• Second Current Reduction
– Current is quickly reduced before electrode
separates, eliminating spatter
– STT circuitry
re-establishes the welding arc at a low
current level
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STT Process
• Peak Current
– High current is applied immediately after the
arc is reestablished
– Arc is momentarily broadened, producing
high heating of the plate, insuring good
fusion and setting the proper arc length
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STT Process
• Tailout
– Current is reduced from peak
to background level
– Reduces agitation of the weld puddle
– This control is a coarse heat control
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Surface Tension Transfer
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STT Process
• High speed video of
arc
STT
click on picture to run video
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STT Process
• High speed video of
arc
click on picture to run video
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STT
STT Process
Sheet Metal Welding With STT
Traditional CV
Short Arc Welding
Welding with STT
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STT Process
Commercial System
Introduced at Essen
1993
• Process Requires
–
–
–
–
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Current and Voltage Sensing
High Speed Switching System
Rapid Control of Output
Rapid Response Power Source
Basic Transformer Design
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Reactor
Inductance Coil
Selects Output
Welding Current
Smoothes / Filters
DC Output
Transformer
Bridge Rectifier
Single Phase Input
High Volts
High Amps
Low Amps
Low Volts
Changes AC to DC
Inverter Technology
DC - Smooth
Low Voltage
High Amperage
DC - Smooth AC - 20,000+ Hz
High Voltage
High Voltage
Low Amperage Low Amperage
AC - 50/60 Hz
DC - Rippled
High Voltage
High Voltage
Low Amperage Low Amperage
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AC - 20,000+ Hz DC - Rippled
Low Voltage
Low Voltage
High Amperage High Amperage
Analog Power Source with Analog Feeder
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Digital Power Source and Digital Feeder,
Software Controlled
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Build it Yourself
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STT Process, Analog Control
• Controls
– Wire feed speed
Adjusts deposition rate
– Peak Current
Controls the arc length
– Background Current
Fine heat input control
– Tailout
Coarse heat input control
– Hot Start
Controls the starting heat
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STT Process, Non-Synergic Digital Control
• Controls
– Wire feed speed
• Adjusts deposition rate
– Peak Current
• Controls the arc length
– Background Current
• Fine heat input control
– Tailout
• Coarse heat input control
– Hot Start
• Controls the starting heat
– Start/End Options
• Preflow, Run-in, Start Time,
Crater, Burnback, Postflow
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STT Process, Synergic Digital Control
• Controls
– Wire feed speed
• Adjusts deposition rate
– Trim
• Adjust ball size and arc energy
– Weld Mode/Arc Control
• Dynamically modifies Hot Start,
Peak, Background, and Tailout
Current
– Start/End Options
• Preflow, Run-in, Start Time,
Crater, Burnback, Postflow
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STT Process
STT open root (viewed from inside
of pipe)
click on picture to run video
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STT Process
Open Root Welding With STT
• Benefits
– Welded open root
ligament or
thickness is large
~ 0.22” (5.6mm)
– Large ligament
eliminates burn
0.22”
(5.6mm) through on next
weld pass.
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STT on Pipe
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With Good Root Fusion
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STT Process
Process Advantages
STT Replacing TIG
– 4 Times Faster
– Vertical Down Welding
Possible
– Consistent X-ray Quality
Welds
– Shorter Training Time
– Welds Stainless, Nickel
Alloys and Mild Steel
– 100% CO2 (on mild steel)
– Various gas mixtures
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STT Replacing Short-arc
– No Lack of Fusion
– Good Puddle Control
– Consistent X-ray Quality
Welds
– Shorter Training Time
– Low Fume Generation &
Spatter
– 100% CO2 (on mild steel)
– Various gas mixtures
STT Process
Open Root Welding With STT
Single-sided
welding
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STT Process
Open Root Welding With STT
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PROCESS CERTIFICATION
STT Process
STT process may
be used in the
following variants
of pipe welding:
•Root pass & basic
coated electrode
for other passes
•Root pass, semiauto welding with
Innershield for
other passes
•For root, fill & cap
passes of pipe up
to 10 mm wall
thickness
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Dual Process Capabilities
• Optimize Quality and Productivity by allowing
process changes in same station
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U.S. Based Organizations with PUBLISHED Rules
for qualification of Short Circuit Transfer Modes
•
•
•
•
•
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American Welding Society
American Bureau of Shipping
American Society of Mechanical Engineers
American Petroleum Institute
Any other code that references ASME SEC IX for
Procedure and Operator Qualification
Welding Cost Analysis, Assumptions
• Labor and Overhead--$70/hr
• Operating Factors
– GTAW—35%
– SMAW—30%
– STT—40%
– FCAW—35%
• GTAW Root Pass at 1.7 ipm
• SMAW Root Pass at 4.4 ipm
• STT Root Pass at 5.5 ipm
• Same Net Material Costs
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Eight Inch Schedule 40 A106B Pipe, 5G
Position
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Process
Time at 100%
Time at
Operating
Factor
Net Labor Cost
per Joint
GTAW Root,
Fill, and Cap
54.35 Minutes
155.3 Minutes
$181.18
GTAW Root,
Balance
SMAW
36.2 Minutes
113.7 Minutes
$132.65
STT Root,
Balance
FCAW
17.0 Minutes
46.9 Minutes
$54.72