Innovative approach of laser assistance in hyperbaric welding

Transcription

1 Innovative approach of laser assistance in hyperbaric welding Supriyo Ganguly, Lecturer in Welding Science Welding Engineering and Laser Processing Centre, Cranfield University Presented at the SMEA annual conference, 17 th June 2014, Sheffield

2 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

3 People involved.. Usani Unoh Ofem Supriyo Ganguly Prof Stewart Williams Welding Engineering and Laser Processing Centre, Cranfield University 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)

4 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

5 Resources MIG/TIG welding 250 bar max. pressure Laser welding 40 bar max. pressure

6 Previous research at Cranfield University

7 Arc stability in hyperbaric process 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 Richardson, IIW Doc. SCUW , 2003

8 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 Surface Plasma? SMA GMA / FCA GTA GTA Qualified FCA Qualified? GMA / FCA Proven Feasibility Any Practical Limit? 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 2500 m

9 The Gas Metal Arc Welding Process At high pressures, keep the arc short to prevent divergence and spatter spray Richardson et al. IIW Doc. SCUW , 1999.

10 Arc Length Self Adjustment ΔV ΔV ΔI ΔI 10 Nixon et al. ICAWT 2000.

11 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). Richardson, IIW Doc. SCUW , 2003

12 Some recent applications of processes developed at the Cranfield University

13 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

14 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

15 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

16 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

17 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

18 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.

19 Innovative application of laser in hyperbaric welding

20 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

21 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

22 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

23 Effect of hyperbaric pressure on cooling rate Thermal cycles Thermal cycles of the weld metal on 25 mm and 5 mm thick plates

24 Effect of hyperbaric pressure on thermal profile cooling time variation Cooling time variation t 8/2 (left) and t 8/5 (right)

25 Effect of hyperbaric pressure on thermal profile Cooling block calibration Experimental set-up Cooling curves Cooling time

26 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.

27 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

28 Comparative study of different advanced power sources 3 m.min -1 WFS/7 m.min -1 TS

29 Comparative study of different advanced power sources 8 m.min -1 WFS/0.42 m.min -1 TS

30 Comparative study of different advanced power sources Heat input and cooling time

31 Comparative study of different advanced power sources Macrographs WFS top row 4 m.min -1 / bottom row 8 m.min -1 GMAW Cold arc CMT GMAW Cold arc CMT

32 Comparative study of different advanced power sources Bead geometry

33 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

34 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

35 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

36 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

37 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

38 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

39 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.

40 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.

41 Study on moisture pick up for laser assisted GMAW Set up Schematic Set-up in the laboratory

42 Study on moisture pick up for laser assisted GMAW Experimental procedure Tests performed as stipulated by BS EN ISO : 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

43 Hydrogen concentration (ml/100g weld metal) Study on moisture pick up for laser assisted GMAW Results showing the reduction CMT LCMT (3 kw, 20 mm) LCMT (3 kw, 0 mm) LCMT (6 kw, 20 mm) Moisture level (ppm) Moisture level vs deposit weld metal hydrogen concentration for CMT and laser assisted CMT Hardness variation in CMT and laser assisted CMT

44 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

45 Future work Application of the advanced power sources within the hyperbaric chamber Application of laser at high pressure

46 Thanks for listening