Spring Material for sea water

Sorry for asking a different question. ( I dared to ask this since
this group cosists of very knowlegable application Engineers).

Can you help me deciding the spring material for sea water application?
.. The spring will be always in contact with the trapped sea water.

Thanks in advance.

 

SS 316 comes to mind but is not very good as spring material, 302/304 will
make better spring but than there is corrosion issue
HTH
Eric

 

If you're going to have the spring actually sitting in a salt water and air
environment, almost anything you use will is going to corrode....I used to
design twistlocks for Cargo shipping containers constantly being exposed to
a salt water environment, and about the only way to keep a serviceable life
of a couple years on the equipment was for any body (housings, ect) to be
heavily hot dip galvanized and internal springs made from 302/304 and coated
(almost encased) in a lot of grease...

Scott

 

Copper Berylium?

 

If there is accessability, you might consider the addition of a
sacrificial annode of some sort ( zinc comes to mind ), mounted in the
vicinity. Regardless of what material is chosen for the spring, the proper
annode will greatly slow the galvanic coorosion.

 

In addition to everything else, keep your eye on what is coming down
the technology pipeline over the next few years.

There are nanotechonology based replacement coatings that are
supposedly better than chromium, particularly in a sea water
environment, according to notes I've read.

The issues of galvanic corrosion will never go away, though as long as
there are conductors in contact with eacy other. When I used to design
sailboats (decades back), we would deliberately use insulator bushings
and pads to isolate direct contact to eliminate as much galvanic action
as possible.

http://www.nanotechwire.com/news.asp?nid=2954&ntid=122&pg=1

Bo

 

"Trapped" sea water is a big problem for 302-304 SS as it is subject to
crevice crack corrosion when Oxygen is eliminated from its environment,
as in a tight sealed, but salt water filled structure.

There are books on the subject, but I don't have mine with me at the
moment. I know they are easy to find online.

Bo

 

Titanium is used extensively for seawater wetted parts. It is pretty
expensive and doesn't necessarily make a good spring though. It all
depends on your application.

 

I don't have any real experience in this area, but I know that stainless
steel is not usually thought of as a good choice for sea water contact.
Bronze seems to be the material of choice for nautical types, so Phosphor
Bronze might be a good starting point for a spring. You have to make the
whole system work together, so your choice may be forced by the other
materials you are using, or you may have to change the other materials to
work with your spring material.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

For use in sea water, I would recommend the following

Assuming spring is cold formed-
Phosphor Bronze Wire ASTM B159/B159M-05
Copper wire ASTM B134
Stainless steel 420 SAE 51420 - least recommended for corrosion, in
comparison to above, although still better than 316, 302 or 304.

Plus an anode and grease

Although, it's hard to recomend anything without seeing the design.

John Layne
www.solidengineering.co.nz

 

I do wonder how much any SS is subject to crevise crack corrosion even
if covered with grease, where salt water actually contacts a high load
end coil with another metal part or where water gets through the grease
somehow.

I haven't revisited this subject in a long time, and this question has
piqued my curiosity.

Bo

 

Could you use an elastomeric "spring" (i.e., urethane or other polymer
shape)?

 

Do you remember what the best grease to use was?

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Mine as well Bo...It's been a few years since I was designing products for
the Maritime environment, and since it had been my first job, my designs
were largely based on the experience of the older engineers experiences who
had been there since the beginning. It'd be interesting to see the advances
in materials and/or practices that can be applied (should I ever go back to
doing that type of work again)...

Scott

 

What greases work best?


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Jerry, when I worked in the Sailboat field designing virtually
everything (keels, rudders, shaft assemblies, rigging, plumbing) we
never used grease on the propeller shafts.

Some people wanted to pay big bucks for Monel as I recall, since it was
a premium product developed for the Navy, if I remember right.
Everyone use sacrificial Zinc anodes on the propeller shaft and the
bottom cleaning guys would replace them as needed.

Then in the late 60s a company came up with a version of SS that was
more resistant to crevice crack corrosion and production boat builders
immediately switche to it as a cost effective and good option.

It was well known however that if you put a fastener through objects
underwater and sealed it up with Polyurethane sealant, that you risked
eventual corrosion where there was no water flow, which has the Oxygen
needed to keep the Chromium Oxide layer on the Stainless Steel. Hence
the desire to have grades of metals not subject to fast crevice crack
corrosion.

Worse than crevice crack corrosion was actual galvanic corrosion from
dissimilar metals or metal grades and worst of all, an electrical leak
that ran from boat to marina, or boat to boat out through a shaft or
through-hull fitting which could destroy a fitting in a few days and
sink a boat.

Those were interesting times.

Bo