Aluminum Welding for Marine & LNG

What marine & LNG service asks of the filler

Marine structures operate for years in seawater, salt spray and the splash zone, where corrosion is the weld's principal failure mode. Al-Mg 5xxx-series alloys and their matching wires offer good corrosion resistance in seawater and contain no copper, markedly reducing the tendency toward pitting and crevice corrosion. They are therefore widely used on superstructures, decks, hull plate, fast craft and aluminium boats, with a mature process and broad adaptability.

LNG (liquefied natural gas) is stored and transported at temperatures down to about −163°C. Aluminium alloys have a face-centred-cubic lattice with no ductile-to-brittle transition of the kind steel exhibits at low temperature, so they retain good toughness and ductility in deep cold. 5xxx Al-Mg welds are therefore widely applied in LNG tanks, cryogenic piping and related inner shells; deep cold is not a process limitation but rather a well-suited service regime for these welds.

Key field-welding considerations

• Pre-weld cleaning: remove the surface oxide film with a stainless-steel brush, then clear oil, salt and moisture with a dedicated solvent to markedly reduce porosity and inclusions. Marine and cryogenic joints are particularly sensitive to cleanliness; proper pre-weld preparation is the basis for joint quality.
• Low-temperature performance: Al-Mg welds retain good toughness in deep cold and deliver stable cryogenic mechanical properties without preheat, suiting LNG tanks and cryogenic piping.
• Shielding gas & wire feeding: use high-purity argon or an argon-helium mix with generous gas coverage to exclude the damp air of marine work, reducing oxidation and porosity. The wire pays off evenly and feeds smoothly, running stably in both manual and mechanised welding and helping to reduce feeding stoppages and downtime.
• Service temperature: 5xxx welds with more than about 3% Mg can sensitise and become susceptible to stress-corrosion if held above 65°C for extended periods. This limit does not apply to LNG cryogenic service, where deep cold is in fact a well-suited operating range for these welds.

The above reflects general field experience. Actual welding parameters, joint design and classification/code requirements should follow your project drawings, the applicable classification-society rules and your qualified procedure (WPS/PQR). For assistance with filler selection or WPS direction, please contact our technical team.