Golden frequency discovered for underwater welding: a breakthrough in durability of marine engineering equipment

Marine facilities including offshore wind piles, bridges and ships suffer from rust, cracks and other defects due to long-term service in harsh underwater environments. While underwater welding is often used for in-service repair, it has limitations such as poor weld formation, insufficient mechanical properties and weak corrosion resistance.

In a study published in the KeAi journal China Welding, a research team from South China University of Technology developed an improved local dry underwater laser welding method by introducing pulsed laser technology and optimizing pulse frequency. The new method enhances the performance of Q355B steel welded joints.

"Q355B low-alloy high-strength steel is widely used in marine engineering, but its underwater welding quality is difficult to guarantee under traditional processes," says Haipeng Liao, corresponding author of the study. "Local dry underwater laser welding combines the advantages of laser precision welding and compact local drying equipment, but the effect of pulse frequency on weld microstructure and performance has not been fully clarified."

To do that, the research team conducted a series of comparative experiments between pulsed laser welding (PLW) and continuous laser welding (CLW). "We found that pulsed laser welds have ripple patterns on the surface and significantly less spatter," shares Liao. "With the increase of pulse frequency, weld penetration depth and bead width show a downward trend, but both are larger than those of continuous laser welds."

The team also found that 80 Hz is the optimal pulse frequency. "At this parameter, the ferrite content in the weld metal reaches the maximum 39%, the elongation reaches 23.1% (93.9% of the base material), and the corrosion resistance reaches 67.0% of the base material, which is much higher than 47.3% of the continuous laser weld," says Liao.

The main innovation of the method lies in its usage of lamellar inorganic-like protection mechanism — pulsed laser periodic thermal cycle reduces molten pool cooling rate, promotes ferrite formation and suppresses martensite, thus balancing strength, plasticity and corrosion resistance.

"This new method solves two major pain points of underwater welding: poor weld formation and insufficient corrosion resistance," notes Liao. "The technology can be directly applied to the repair and manufacturing of offshore wind power, ships, cross-sea bridges and other major equipment, and provides theoretical and data support for the engineering application of local dry underwater laser welding."

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Contact the author: Haipeng Liao, School of Mechanical & Automotive Engineering, South China University of Technology, Guangzhou, China, liaohaipeng@scut.edu.cn

The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).

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