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Enhanced Surface Tension Transfer for Pipe Welding

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Title: Enhanced Surface Tension Transfer for Pipe Welding


1
Enhanced Surface Tension Transfer for Pipe Welding
  • Harry Sadler
  • Manager Military and Shipbuilding Sales

2
Customer Assistance Policy
The business of The Lincoln Electric Company is
manufacturing and selling high quality welding
equipment and consumables, and cutting equipment.
Our challenge is to meet the needs of our
customers and to exceed their expectations. On
occasion, purchasers may ask Lincoln Electric for
advice or information about their use of our
products. We respond to our customers based on
the best information in our possession at that
time. Lincoln Electric is not in a position to
warrant or guarantee such advice, and assumes no
liability, with respect to such information or
advice. We expressly disclaim any warranty of
any kind, including any warranty of fitness for
any customers particular purpose, with respect
to such information or advice. As a matter of
practical consideration, we also cannot assume
any responsibility for updating or correcting any
such information or advice once it has been
given, nor does the provision of information or
advice create, expand or alter any warranty with
respect to the sale of our products. Lincoln
Electric is a responsive manufacturer, but the
selection and use of specific products sold by
Lincoln Electric is solely within the control of,
and remains the sole responsibility of, the
customer.
3
Conventional Short Circuit Transfer
4
Traditional Short Circuit Transfer
click on picture to run video
5
STT Process
Research Began July,1985
  • Purpose
  • Develop a semi - automatic short circuiting
    welding process which eliminates spatter when
    using 100 CO2 shielding gas.

6
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.

7
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

8
STT Process
STT Welding Arc
9
STT Process
  • Background current
  • Arc current level prior to shorting to the weld
    pool.
  • Contributes to the overall heat input
  • Keeps arc lit

10
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

11
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.

12
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

13
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

14
STT Process
  • Tailout
  • Current is reduced from peak to background
    level
  • Reduces agitation of the weld puddle
  • This control is a coarse heat control

15
Surface Tension Transfer
16
STT Process
  • High speed video of STT arc

click on picture to run video
17
STT Process
  • High speed video of STT arc

click on picture to run video
18
STT Process
Sheet Metal Welding With STT
Traditional CV Short Arc Welding
Welding with STT
19
STT Process
Commercial SystemIntroduced at Essen1993
  • Process Requires
  • Current and Voltage Sensing
  • High Speed Switching System
  • Rapid Control of Output
  • Rapid Response Power Source

20
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
21
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
22
Analog Power Source with Analog Feeder
23
Digital Power Source and Digital Feeder, Software
Controlled
24
Build it Yourself
25
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

26
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

27
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

28
STT Process
  • STT open root (viewed from inside of pipe)

click on picture to run video
29
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)
30
STT on Pipe
31
With Good Root Fusion
32
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

33
STT Process
Open Root Welding With STT
  • Single-sided welding

34
STT Process
Open Root Welding With STT
35
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

36
Dual Process Capabilities
  • Optimize Quality and Productivity by allowing
    process changes in same station

37
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

38
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

39
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
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