Innovative approach of laser assistance in hyperbaric welding

Supriyo Ganguly, Lecturer in Welding Science Welding Engineering and Laser Processing Centre, Cranfield University

s.ganguly@cranfield.ac.uk 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

6

8

10

12

14

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