Enhanced Surface Tension Transfer for Pipe Welding

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Enhanced Surface Tension Transfer for Pipe Welding

• Harry Sadler
• Manager Military and Shipbuilding Sales

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equipment and consumables, and cutting equipment.
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and remains the sole responsibility of, the
customer.
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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 STT arc

click on picture to run video
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STT Process

• High speed video of STT arc

click on picture to run video
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STT Process
Sheet Metal Welding With STT
Traditional CV Short Arc Welding
Welding with STT
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STT Process
Commercial SystemIntroduced at Essen1993

• Process Requires
• Current and Voltage Sensing
• High Speed Switching System
• Rapid Control of Output
• Rapid Response Power Source

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Basic Transformer Design
Reactor Selects Output Welding Current
Inductance Coil Smoothes / Filters DC Output
Bridge Rectifier Changes AC to DC
Transformer Single Phase Input High Volts High
Amps Low Amps Low Volts
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Inverter Technology
DC - Smooth Low Voltage High Amperage
DC - Smooth High Voltage Low Amperage
AC - 20,000 Hz High Voltage Low Amperage
AC - 50/60 Hz High Voltage Low Amperage
DC - Rippled High Voltage Low Amperage
AC - 20,000 Hz Low Voltage High Amperage
DC - Rippled Low Voltage High Amperage
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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 through on next
  weld pass.

0.22 (5.6mm)
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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 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 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 Process
Open Root Welding With STT

• Single-sided welding

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STT Process
Open Root Welding With STT
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STT Process
PROCESS CERTIFICATION

• STT process may be used in the following variants
  of pipe welding
• Root pass basic coated electrode for other
  passes
• Root pass, semi-auto 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

• 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

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Welding Cost Analysis, Assumptions

• Labor and Overhead--70/hr
• Operating Factors
• GTAW35
• SMAW30
• STT40
• FCAW35
• 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
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