Evaluation of pre- and post-laser treatment effects of welds in maritime industry
Väisänen, Inka (2025-03-28)
Evaluation of pre- and post-laser treatment effects of welds in maritime industry
(28.03.2025)
Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
avoin
Julkaisun pysyvä osoite on:
https://urn.fi/URN:NBN:fi-fe2025041527444
https://urn.fi/URN:NBN:fi-fe2025041527444
Tiivistelmä
Corrosion heavily impacts maritime industry as it has very often welded structures, and they are the especially prone to the effects of corrosion This may lead to mechanical failure, as the welds are vulnerable to the damage. Compared to conventional cleaning methods that are used in maritime industry, such as sand blasting or grinding, laser cleaning is a method where the laser beam removes dirt, oil or other unwanted component from surface without damaging the substrate material below it. Laser polishing can decrease the surface roughness as a post-process by melting the surface layer of the metal with a laser pulse. The melted metal smoothens with surface tension and hardens quickly to form an even surface.
The aim of this thesis is to research if the laser cleaning as a pre-processing method and laser polishing as a post-processing method are beneficial when welds in material EH36 are used in maritime industry. Laser polishing was also tested as a post-processing method for 316 L stainless steel manufactured by laser bed powder fusion method (PBF-LB/M).
The laser processes were executed with an IPG YLPN nanosecond pulsed fiber laser with a maximum average power of 100W The wavelength is minimum 1055 nm and maximum 1075 nm (typically 1064 nm). The samples were first laser cleaned and conventionally cleaned with a cylindrical grinding setup, and then laser polished from the top and bottom sides of the weld. The PBF-LB/M samples were only laser polished. A Gamry instruments surface corrosion system and an Ivium electrochemical analyser were used to test and analyse the corrosion properties. The roughness values were obtained with Bruker Alicona Infinite Focus G6 along with the surface inspection.
The laser power was varied between 25 W – 100 W and the pulse width was varied between 25 – 100 ns The best results for laser cleaning were achieved with the average power of 25 W and pulse width of 75 ns. The optimal parameters for laser polishing were with the average power of 75 W and pulse width of 25 ns. The process speed was 450 mm/s and the pulse frequency was set to 10 kHz for both laser processes. The number of treatment rounds were set to six.
From the results it can be concluded that visually the laser cleaning was successful when compared to the conventionally cleaned sample as no rust or oil can be seen in the microscopic images. The surface roughness of the laser cleaned sample was also reduced, when compared to the conventionally cleaned sample, as the areal average roughness Sa was decreased 36 %. When laser polishing was studied as post-treatment for welds, laser polishing improved the Sa 22 % compared to the laser cleaned sample. The corrosion rate was lowered in the laser polished sample 68 %, when compared to the laser cleaned sample. Laser polishing also improved the surface roughness of 316L as the Sa value lowered 66 % compared to the non-laser polished 316 L sample. Additionally, the corrosion rate was reduced in the laser polished 316 L PBF-LB/M sample, it was 31 % less than the non-laser polished sample.
As corrosion has such high impact on maritime industry, improving the materials is vital. The results in this thesis indicate that the laser cleaning is a reasonable option to conventional cleaning methods. Material surface could be modified with a laser to be more resistant to corrosion without any additional materials or coatings.
The aim of this thesis is to research if the laser cleaning as a pre-processing method and laser polishing as a post-processing method are beneficial when welds in material EH36 are used in maritime industry. Laser polishing was also tested as a post-processing method for 316 L stainless steel manufactured by laser bed powder fusion method (PBF-LB/M).
The laser processes were executed with an IPG YLPN nanosecond pulsed fiber laser with a maximum average power of 100W The wavelength is minimum 1055 nm and maximum 1075 nm (typically 1064 nm). The samples were first laser cleaned and conventionally cleaned with a cylindrical grinding setup, and then laser polished from the top and bottom sides of the weld. The PBF-LB/M samples were only laser polished. A Gamry instruments surface corrosion system and an Ivium electrochemical analyser were used to test and analyse the corrosion properties. The roughness values were obtained with Bruker Alicona Infinite Focus G6 along with the surface inspection.
The laser power was varied between 25 W – 100 W and the pulse width was varied between 25 – 100 ns The best results for laser cleaning were achieved with the average power of 25 W and pulse width of 75 ns. The optimal parameters for laser polishing were with the average power of 75 W and pulse width of 25 ns. The process speed was 450 mm/s and the pulse frequency was set to 10 kHz for both laser processes. The number of treatment rounds were set to six.
From the results it can be concluded that visually the laser cleaning was successful when compared to the conventionally cleaned sample as no rust or oil can be seen in the microscopic images. The surface roughness of the laser cleaned sample was also reduced, when compared to the conventionally cleaned sample, as the areal average roughness Sa was decreased 36 %. When laser polishing was studied as post-treatment for welds, laser polishing improved the Sa 22 % compared to the laser cleaned sample. The corrosion rate was lowered in the laser polished sample 68 %, when compared to the laser cleaned sample. Laser polishing also improved the surface roughness of 316L as the Sa value lowered 66 % compared to the non-laser polished 316 L sample. Additionally, the corrosion rate was reduced in the laser polished 316 L PBF-LB/M sample, it was 31 % less than the non-laser polished sample.
As corrosion has such high impact on maritime industry, improving the materials is vital. The results in this thesis indicate that the laser cleaning is a reasonable option to conventional cleaning methods. Material surface could be modified with a laser to be more resistant to corrosion without any additional materials or coatings.