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Cadmium coated bolts / nuts vs. stainless steel bolts for seawater exposure


We are trying to determine the best / longest lasting materials for metallic hardware items (nuts, bolts, washers) in an underwater sea-water / salt water exposure (a pipe line).

Will a cadmium coated steel perform better or worse underwater than will a stainless steel material? Should the stainless steel material be coated as well?

Kenneth R. Martin
Aquatic Design & Engineering, Inc. - Oakland, Florida, USA


Much worse. Cadmium plating 0.0005" thick, yellow chomated, may last 1 week before white rust and 1-6 months before red rust. Somewhat illegal due to toxicity.

No, use a suitable grade of stainless. For fasteners, 2205 (UNS S31803) is better than 316 with respect to strength and resistance to crevice & pitting corrosion & SCC. What is the pipeline material -- coated steel, stainless, reinforced plastic...? Galvanic compatibility may be an issue.

The best long-term material for both pipeline and hardware is probably titanium.

Ken Vlach
- Goleta, California honored Ken for his countless helpful
& well researched responses. He 'disappeared' in
2008, never answering our several inquiries about
his situation. But we believe that this is his obit
and would greatly appreciate hearing from anyone
who knew him. Thank you Ken, and rest in peace.


Cadmium plated steel bolts are not suitable for seawater usage, and neither are most stainless steels. The proper choice of fastener depends a great deal on what is being joined (geometry, materials, stresses, etc.). Nickel-based alloys like MONEL K-500 or INCONEL 686 or Titanium alloys like TIMETAL 5111 are the most resistant to corrosion and offer high strength and toughness. However, if the stresses are not too high, a duplex stainless steel grade like 254SMO (UNS S31254) may be acceptable.

Toby Padfield
Automotive module supplier - Michigan

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