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 customer’s 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. Working Prototype January,1987
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. Working Prototype January,1987
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. Sheet Metal Welding With STT
STT Process
Sheet Metal Welding With STT
Traditional CV
Short Arc Welding
Welding with STT

19. Commercial System Introduced at Essen 1993
STT Process
Commercial System Introduced at Essen 1993
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
Transformer
Single Phase Input
High Volts High Amps
Low Amps Low Volts
Bridge Rectifier
Changes AC to DC

21. Inverter Technology DC - Smooth High Voltage Low Amperage
AC - 20,000+ Hz
High Voltage
Low Amperage
DC - Smooth
Low Voltage
High 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. Open Root Welding With STT
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 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
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

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

34. Open Root Welding With STT
STT Process
Open Root Welding With STT

35. 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, 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
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

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