Thermodynamic considerations of pore formation and hydrostatic pressure during underwater wet welding

Abstract

The pore and crack formations in the weld bead during underwater wet welding are the main cause of failure to reach the required mechanical properties of the weld metal. These defects are closely associated with the decomposition of the water molecule under electric arc conditions. In this paper, the thermodynamic calculations of the complex process of the water decomposition under the conditions of high electric arc temperatures at a pressure of 1 atm of steam are discussed. The values of the partial pressures of the five main products of the vaporizations and decomposition of the water (H₂O_(g), H₂, O₂, H and O) are calculated for temperatures between 1870 and 4000 K. Due to the fact that atomic hydrogen is mainly responsible for pore formation in the weld metal, its partial pressure as a function of partial pressures of atomic oxygen and steam (water vapour) is expressed. Hydrogen solubility values in the liquid metal under the conditions of underwater wet welding at depths of 50 and 100 m, and a comparison between the thermodynamic calculation and porosity measurement results at depths of 50 and 100 m, are presented.

Keywords:

• underwater wet welding
• pore formation
• thermal water decomposition

Acknowledgements

The authors of this work would like to thank CAPES (No. 038/08) and CNPq (No. 495130/2004–8) for the support provided in the execution of the investigation projects that made it possible to obtain the results presented here.

Notes

1. [email protected]

2. [email protected]

3. [email protected]

4. [email protected]

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Additional information

Notes on contributors

Rafael Quintana Puchol

1 1. [email protected]

Lorenzo Perdomo González

2 2. [email protected]

Alejandro Duffus Scott

3 3. [email protected]

Alexandre Queiroz Bracarense

4 4. [email protected]

Ezequiel Caires Pereira Pessoa

5 5. [email protected]