finishing.com logo
    HOME / sitemapFAQsBOOKSHelp WantedsAdvertiseContact   you are here: Hotline/Forum => Letter 43834
most fun in metal finishing

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  

Ken received a special
"Contributor of the Year" award
from finishing.com for his numerous
helpful and well researched responses


+++++++

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

ADD a Q or A to THIS thread START a NEW THREADView This Week's HOT TOPICS

disclaim

 seek

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & DevicesUsed & Surplus


©1995-2014 finishing.com     -    Privacy    -    Search