Shipbuilding and Offshore

Seawater is the most aggressive natural electrolyte: roughly 19,000 ppm chloride, plus wet–dry cycles and crevices. Here the first criterion is not strength — it is whether the material survives crevice corrosion.

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Typical parts and material selection

Part	Grade	Surface / size	Watch for
Deck railing / fittings	316L	Tube / profile, polished	Salt spray, post-weld passivation
Seawater piping	2205 / 6Mo	Seamless / welded tube	Pitting, flow erosion
LNG tank inner shell	304L / 304	Plate 8–50 mm	Low-temperature toughness, class approval
Accommodation / galley equipment	304 / 316L	8–2 mm, 2B/HL	Cleanability, fingerprint resistance
Fasteners / fixings	316 / 2205	Bar / forging	Stress corrosion cracking

These are the usual configurations.Actual selection depends on the medium, temperature and welding method— the same part may move from 304 to 316L or 2205. Describing the service conditions is more useful than naming a grade.

Three real constraints in this industry

Crevice corrosion is the dominant failure

Under joints and at support-to-hull contacts, 304 shows rust within a few months. Eliminate the crevice in the design (continuous welds, drain holes) and upgrade to 316L or 2205.

Confirm class approval from the start

DNV / ABS / LR / CCS each maintain their own approved material lists. A better grade that is not approved will still fail inspection — verify it at the quotation stage.

Weld distortion accumulates through to assembly

Thin equipment parts distort and the error accumulates in the final assembly. Prefabricate in sections with anti-distortion jigs and leave trimming allowance.