Summary for cadmium coated bolts seawater Discussion
Cadmium coated bolts vs stainless steel for seawater exposure is answered pretty bluntly in the thread: cadmium-plated steel is a poor choice for submerged saltwater service. Ken Vlach says cadmium plating is much worse than stainless in seawater, may show white rust in about a week and red rust within 1-6 months, and is also problematic because of toxicity. He recommends using a suitable stainless grade instead, noting that 2205 duplex stainless is better than 316 for strength and for crevice, pitting, and stress-corrosion resistance, while also warning that galvanic compatibility with the pipeline material matters and that titanium may be the best long-term option. Toby Padfield adds that cadmium-plated steel bolts are not suitable for seawater and that many stainless steels are also inadequate; he suggests higher-performance alloys such as Monel K-500, Inconel 686, titanium alloys, or possibly 254SMO if stresses are modest. A later question about aluminum structures in submerged saltwater raises galvanic concerns and asks for alternatives to stainless, zinc, titanium, and nickel.
Q. 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
2007
A. 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 [deceased]
– Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007
A. 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
2007
Q. Hello, I am also considering using cadmium coating threaded rods for anchoring into concrete in submerged saltwater application. Per your previous comment, cadmium is no good for saltwater. Also, looked at Aluminum-Bronze but very expensive. My base material as aluminum, as well as all other existing metal framing. Galvanic action has been huge issue in the past and we must eliminate all stainless steel and zinc materials. Titanium and Nickel also on the wrong end of the spectrum for Aluminum. Do you have any other recommendations or I just bite the bullet with AL-Bronze?
Tirrell Day
Engineering – Tampa, Florida, United States
October 28, 2019