Innovative approach of laser assistance in hyperbaric welding · Innovative approach of laser...
Transcript of Innovative approach of laser assistance in hyperbaric welding · Innovative approach of laser...
Innovative approach of laser assistance in hyperbaric welding
Supriyo Ganguly, Lecturer in Welding Science Welding Engineering and Laser Processing Centre, Cranfield University
[email protected] Presented at the SMEA annual conference, 17th June 2014, Sheffield
About this work…
This work was performed with the following funding: Group sponsored project with TWI
Petrobras, Brazil BP and TWI
PhD studentship sponsored by Petroleum Technology Development Fund (PTDF), Nigeria
People involved..
Usani Unoh Ofem Supriyo Ganguly Prof Stewart Williams Marcello Consonni of TWI and Neil Woodward of Isotek Oil & Gas Ltd. The presenter has shown here some work of Statoil in the Asgard Subsea Compression project (ASCP)
Welding Engineering and Laser Processing Centre, Cranfield University
Presentation outline
A brief history and research outcome on the previous research on dry hyperbaric welding at Cranfield
The innovative idea of applying laser in hyperbaric application
Resources
•MIG/TIG welding •250 bar max. pressure •Laser welding
•40 bar max. pressure
Previous research at Cranfield University
Hyperbaric arcs behave like electromagnetic plasma jets
Stability deteriorates with increasing pressure due to gas flow conditions and arc root contraction
Electrode erosion increases with pressure due to rising energy density
Details are often highly condition specific
Arc stability in hyperbaric process
Richardson, IIW Doc. SCUW-202-03, 2003
Depth feasibility for different arc welding processes
Approximate depth ranges for different arc welding processes
GTA / plasma –
enforced arc stability GMA / FCA –
controlled arc instability
0 m
50 m
100 m
150 m
200 m
250 m
300 m
350 m
400 m
450 m
500 m
550 m
600 m
650 m
700 m
1000 m
GTA
GMA / FCA
Plasma
SMA
Surface
GTA Qualified
FCA Qualified?
?
GMA / FCA Proven
Feasibility 2500 m
Any Practical Limit ?
At high pressures, keep the arc short to prevent divergence and spatter spray
The Gas Metal Arc Welding Process
Richardson et al. IIW Doc. SCUW 176-99, 1999.
10
Nixon et al. ICAWT 2000.
ΔV
ΔI
ΔI
ΔV
Arc Length Self Adjustment
. . . . At high pressures (below about 800 m, 2,625 ft), the arc is
dominated by metal vapour and voltage is almost independent of
pressure.
Process control requirements and process behaviour are
independent of pressure
Process is insensitive to water depth; hence no depth limitation -
proven to 2,500 m (8,200 ft), expect process will be stable well
below 5000 m (16,400 ft).
Arc Length Self Adjustment
Richardson, IIW Doc. SCUW-202-03, 2003
Some recent applications of processes developed at the Cranfield University
Remote Hyperbaric GMA Welding - Beyond Diver Depths
• 2 Applications:
– Pipeline Sleeve Repair
– Remote Hot Tap
• Dry Hyperbaric GMA Weld Procedures developed and tested in the
Cranfield Lab. have been tested Offshore in Deep Water Tests
– 370msw and 980msw for Pipeline Sleeve Repair
– 270msw and 350msw for Remote Hot Tap
Applications: Sleeve Repair
Weld Sleeve Repair Application Fillet Weld Build-Up 157 passes and 22hrs Arc-On
Time for 42” Åsgard Transport 121 passes for 30” Ormen Lange
with 11.7 hrs Arc-On Time
APPLICATIONS: REMOTE HOT TAP
• Retrofit Tee to provide full flexibility & independence when selecting tie-in location
• Cost effectiveness • Utilize spare transport capacity
in pipeline systems • Remote = beyond diver depths
Remote (Diver-less) Welding Equipment
Equipment
• Remote Hot Tap Cutting (through a Valve Module)
• Remote Hot Tap Cutter previously used at 145msw for the Tampen Link project and at 960msw for the Ormen Lange project
Remote (Diverless) Welding Equipment - First Retrofit Tee
•Welding system contains all functions for making
and monitoring the internal weld
•Remote installation of a structural
reinforcement clamp containing the
branch pipe
•Pressure barrier made by internal weld
inside the branch pipe
Goals: Retrofit tee
Reduced cost for future infrastructure development Increased depth and pressure capability
Åsgard Subsea Compression Project to improve recovery from the Mikkel and Midgard reservoirs by around 280 million barrels of oil equivalents.
Innovative application of laser in hyperbaric welding
Context
Offshore hyperbaric welding is susceptible to compromise in weld metal integrity due to very high cooling rates that may give rise to;
• Shear transformed phases which are hard and susceptible to cracking • Moist environment may lead to hydrogen assisted cracking
The present research is focussed on how application of laser would be beneficial towards reduction of cooling rate and hydrogen diffusion in order to improve weld metal integrity
Outline of the present research
Determine the effect of incumbent pressure on cooling rate for different thicknesses
A comparative study of different advanced GMAW power sources to understand the heat input (carried out at normal atmospheric pressure)
Study on the effect of laser towards changing the cooling conditions
Study on the effect of laser on moisture removal
Effect of hyperbaric pressure on cooling rate – experimental set-up
The study was carried out in two different thicknesses 25 mm and 5 mm
Also a cooling block calibration was done to understand the convective heat loss to generate data for modelling
Effect of hyperbaric pressure on cooling rate – Thermal cycles
Thermal cycles of the weld metal on 25 mm and 5 mm thick plates
Effect of hyperbaric pressure on thermal profile – cooling time variation
Cooling time variation t8/2 (left) and t8/5 (right)
Effect of hyperbaric pressure on thermal profile – Cooling block calibration
Experimental set-up Cooling curves Cooling time
Summary – effect of hyperbaric pressure on thermal cycle
• In thicker sections, conduction is the principle mode of cooling. The incumbent pressure does not play a major role in the cooling profile in thicker sections • In thinner sections pressure is important in determining the cooling rate and thereby would influence metallurgical phase formation • Since hyperbaric welding is done in thicker sections, it is less likely that the depth of welding would have any significance on the cooling cycle.
Comparative study of different advanced power sources - Method
Welding parameters 3 m/min – 8 m/min WFS 0.42 m/min travel speed CTWD - 10 mm 15 l/min gas flow rate
Equipment: Fronious TPS CMT, EWM ColdArc and ESAB LUD 450 Power Sources, and ABB Robot
Materials: X65 pipeline steel, G4Si1 filler wire and 100% Argoshield Heavy shielding gas
Comparative study of different advanced power sources – Waveforms @ 3 m.min-1 WFS/7 m.min-1 TS
Comparative study of different advanced power sources – Waveforms @ 8 m.min-1 WFS/0.42 m.min-1 TS
Comparative study of different advanced power sources – Heat input and cooling time
GMAW Cold arc CMT
GMAW Cold arc CMT
Comparative study of different advanced power sources – Macrographs WFS top row 4 m.min-1/ bottom row 8 m.min-1
Comparative study of different advanced power sources – Bead geometry
Summary – Comparison between different power sources
• The CMT process distinctively showed lower heat input and thereby cooling time through the critical temperature range • Both the advanced power sources, generated defect free welds, however, lower heat input in CMT process even resulted in lower spatter generation
Laser assisted GMAW – Set up
Fronius TPS power source and IPG YLR-8 kW fibre laser
Welding parameters - constant WFS (5 m/min) and travel speed (0.42 m/min) and variable laser parameters -
Beam diameter – 10 mm, 15 mm and 20 mm Laser power – 1 kW, 3 kW and 6 kW Process distance – 0 mm, 5 mm, 10 mm, 15 mm and 20 mm
Laser assisted GMAW– Results with 20 mm φ and 6 kW power, 0 mm process distance
Thermal cycles of CMT and laser plus CMT
Effect of process distance
Laser assisted GMAW– Results: Effect of process distance (constant power 6 kW) and specific point energy (constant process distance 5 mm)
Specific point energy = Power density (p/A) × interaction time (d/v) × Area (A) Where p – power, d – beam diameter, v – travel speed and A – area of laser beam
Laser assisted GMAW– Macrographs
CMT bead with WFS 5 m.min-1 Laser assisted CMT bead WFS 5 m.min-1 and laser power 6 kW, beam φ 20 mm and process distance 20 mm
Laser assisted GMAW– Hardness variation : CMT, CMT + Laser (20 mmφ, 20 mm process distance)
CMT - WFS 5 m.min-1 CMT - WFS 5 m.min-1+ laser power 3 kW & 5 kW
Summary – Laser assisted GMAW
• Laser assistance can be a useful to control the heat input and therefore, the cooling rate and hardness of the resulting microstructure • Application of laser also re-shaped the bead with a smoother transition between the bead and the substrate • Laser energy and the spatial resolution of its application area can be controlled to a very high degree which may be of specific interest for this application.
Study on moisture pick up for laser assisted GMAW
The aim of this study is to investigate the effectiveness of using a laser to reduce or minimise the diffusible weld metal hydrogen content.
The objectives are as follows:
• To analyse the weld metal hydrogen content during GMAW (CMT) and laser assisted GMAW (CMT) welding by introducing varying levels of moisture into the shielding gas and
• Evaluate the influence of laser processing conditions on the removal of diffusible hydrogen from the weld metal.
Study on moisture pick up for laser assisted GMAW – Set up
Schematic Set-up in the laboratory
Study on moisture pick up for laser assisted GMAW – Experimental procedure
Tests performed as stipulated by BS EN ISO 3690-2001: Welding and Allied Processes-Determination of Hydrogen Content in Ferritic Steel Arc Weld Metal
Welding parameters - constant WFS (7 m/min) and travel speed (0.42 m/min) o Beam diameter – 10 mm, and 20 mm o Laser power –3 kW and 6 kW o Process distance – 0 mm and 20 mm o Moisture levels: 300 (dry gas), 3000, 6000, 10000
Moisture level vs deposit weld metal hydrogen concentration for CMT and laser assisted CMT
Study on moisture pick up for laser assisted GMAW – Results showing the reduction
0
2
4
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10
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0 3000 6000 9000 12000
Hyd
rog
en
co
nce
ntr
ati
on
(m
l/1
00
g w
eld
me
tal)
Moisture level (ppm)
CMT
LCMT (3 kW, 20 mm)
LCMT (3 kW, 0 mm)
LCMT (6 kW, 20 mm)
Hardness variation in CMT and laser assisted CMT
Summary – Study on moisture pick up
• The study showed a systematic increase in weld metal hydrogen content with rise in moisture in the shielding gas
• Laser is useful in reducing the diffusible hydrogen
• Increase in laser heat input is more effective in removal
Future work
• Application of the advanced power sources within the hyperbaric chamber
• Application of laser at high pressure
Thanks for listening