Dry hyperbaric welding of HSLA steel up to 35 bar ambient pressure with CMT arc mode

  • Ivan BunazivEmail author
  • Ragnhild Aune
  • Vigdis Olden
  • Odd M. Akselsen


Hyperbaric welding plays a significant role in subsea pipeline installations and repairs for transport of oil and gas from the offshore field to the market. The effect of ambient pressure, from 1 to 35 bar, on penetration depth and microstructure evolution in dry hyperbaric welding of X70 pipeline steel has been investigated. It was found that penetration depth is increasing with increased ambient pressure due to enhanced melt flow by using the cold metal transfer (CMT) arc mode. Increase ambient pressure lowered process stability causing more spattering strongly affecting current/voltage characteristics of the arc. Numerical simulation showed very fast cooling rate regardless ambient pressure effect causing hard microstructure. Application of lower alloyed wire provided lower hardenability and higher fraction of the allotriomorphic ferrite with high acicular ferrite volume fraction. Chemical analysis revealed positive effect of low oxygen/nickel with high silicon containing wire for acicular ferrite nucleation in weld metal at any process parameters due to higher activity of inclusions.


Dry hyperbaric welding Cold metal transfer Numerical simulation Microstructure HSLA steel Non-metallic inclusions 



Specific heat (J kg−1 °C−1)


Electromagnetic force (N m−3)


Mass proportion of molten material


Standard acceleration due to gravity (9.8 m s−2)


Enthalpy (kg m2 s−2)


Latent heat of fusion (230,000 J kg−1 °C−1)


Heat transfer coefficient for convection (50 W m−2 °C−1)


Arc current (A)


Thermal conductivity (W m−1 °C−1)


Characteristic length which is approximated by 1/8 of weld pool width (m)


Length of weld pool (m)


Outward normal vector of top surface


Power of the Gaussian surface heat source (W)


Arc pressure (N m−2)


Heat input of the volumetric heat source model (kJ/mm)


Total heat flux of the heat source (W m−3)


Radius of the Gaussian surface heat source (m)


Radius of arc at welding electrode (m)


Radius of arc at weld pool surface (m)


Ambient temperature (20 °C)


Liquidus temperature (1512 °C)


Solidus temperature (1472 °C)


Arc voltage (V)


Momentum diffusitivity or kinematic viscosity (m2 s−1)


Characteristic (or maximum) melt velocity in weld pool (m s−1)


Volumetric heat source travel speed (mm/min)

Greek symbols


Thermal diffusivity (m2 s−1)


Thermal expansion coefficient (1.0 × 10−5 m m−1 °C−1)


Temperature difference of maximum temperature in weld pool and solidus temperature (°C)


Thermal gradient of surface tension (− 0.35 × 10−4 N m−1 °C−1)


Emissivity rate (0.5)


Arc efficiency (0.8 for GMAW process)


Permeability in a vacuum (1.257 × 10−6 N A−2)


Dynamic viscosity of the liquid metal (N s m−2)


Viscosity of the liquid metal (3 × 10−2 kg m−1 s−1)


Magnetic permeability (1.26 × 10−6 N A−2)


Density of the liquid metal (6800 kg m−3)


Density of the solid metal (7800 kg m−3)


Stefan-Boltzmann constant (5.67 × 10−8 W m−2 °C−4)



SINTEF Molab AS is appreciated for oxygen content measurements. Sigurd Wenner (SINTEF Industry) is appreciated for SEM and EDS data.

Funding information

The authors received funding from the Research Council of Norway through the Petromaks 2 Programme, Contract No. 234110/E30. The financial support was also received from Statoil Petroleum AS, Gassco AS, Technip Norge AS, EFD Induction AS, and Pohang Iron and Steel Company Posco.


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Copyright information

© Springer-Verlag London Ltd., part of Springer Nature 2019

Authors and Affiliations

  • Ivan Bunaziv
    • 1
    Email author
  • Ragnhild Aune
    • 1
  • Vigdis Olden
    • 1
  • Odd M. Akselsen
    • 1
  1. 1.SINTEF IndustryTrondheimNorway

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