I received two 7x15 stainless ports today. When I ordered them I was
assured they were 316 ss. So today I thought I would see if a magnet
would stick on one. The magnet stuck. When I called the supplier about
another issue I mentioned that my magnet was sticking to the 316 ss
port. I was told the polishing process was to blame and the 316 had
"picked up a slight magnetic" charge.

Is that true?

Are there simple NDT methods to determine if a stainless alloy is 304
or 316?
Bob

Your supplier is handing you a bunch of crap. You might want to try and
get your money back.

Magnetic property is not a valid test for determining the difference between
304 and 316 stainless. There are test kits but they cost more than your
hatches. The "official" test is to put a drop each of concentrated
hydrochloric and nitric acid on the sample. After 3 or 4 minutes move them
to a slide and add 2 drops of potassium thiocyanate. Add a little 25%
sodium thiosulfate and stir. If the final color is violet it contains
molybdenum and is 316. (Aren't you sorry you asked.) :-)

Both can become slightly magnetic when cold worked. If a stainless casting
is then cold forged to finished dimensions or milled it can gain a little
magnetic permeability. The only way you can be assured of quality is to be
sure of the manufacturer. The name brand people like Hood, Bomar, Lewmar
and New Found Metals can't afford to use anything less than they advertise.
The difference in price between 304 and 316 casting ingots is not enough
compared to the fabrication costs.

OTOH, magnetism induced during polishing is something I would think about.
That can be an indication that free iron molecules were left on the surface
and unless it is passivated or electropolished you can get some rust
staining. The stain will come off with a little work and usually does not
leave pitting

Welds are another place where the alloys can migrate and leave free iron
ions unless it is passivated after welding. That can cause real problems.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Bob" wrote in message
oups.com...
I received two 7x15 stainless ports today. When I ordered them I was
assured they were 316 ss. So today I thought I would see if a magnet
would stick on one. The magnet stuck. When I called the supplier about
another issue I mentioned that my magnet was sticking to the 316 ss
port. I was told the polishing process was to blame and the 316 had
"picked up a slight magnetic" charge.

Is that true?

Are there simple NDT methods to determine if a stainless alloy is 304
or 316?
Bob

Take your magnet with you the next time you go to the auto store and test
the stainless hose clamps. Some will be completely non-magnetic, some just
the band will be non-magnetic and some will be completely magnetic. But they
all claim to be stainless! I only buy the completely non magnetic versions,
especially for the boat!
Gordon


"Glenn Ashmore" wrote in message
news:46hAf.11411$Dh.5793@dukeread04...
Magnetic property is not a valid test for determining the difference
between
304 and 316 stainless. There are test kits but they cost more than your
hatches. The "official" test is to put a drop each of concentrated
hydrochloric and nitric acid on the sample. After 3 or 4 minutes move
them
to a slide and add 2 drops of potassium thiocyanate. Add a little 25%
sodium thiosulfate and stir. If the final color is violet it contains
molybdenum and is 316. (Aren't you sorry you asked.) :-)

Both can become slightly magnetic when cold worked. If a stainless
casting
is then cold forged to finished dimensions or milled it can gain a little
magnetic permeability. The only way you can be assured of quality is to be
sure of the manufacturer. The name brand people like Hood, Bomar, Lewmar
and New Found Metals can't afford to use anything less than they
advertise.
The difference in price between 304 and 316 casting ingots is not enough
compared to the fabrication costs.

OTOH, magnetism induced during polishing is something I would think about.
That can be an indication that free iron molecules were left on the
surface
and unless it is passivated or electropolished you can get some rust
staining. The stain will come off with a little work and usually does not
leave pitting

Welds are another place where the alloys can migrate and leave free iron
ions unless it is passivated after welding. That can cause real problems.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Bob" wrote in message
oups.com...
I received two 7x15 stainless ports today. When I ordered them I was
assured they were 316 ss. So today I thought I would see if a magnet
would stick on one. The magnet stuck. When I called the supplier about
another issue I mentioned that my magnet was sticking to the 316 ss
port. I was told the polishing process was to blame and the 316 had
"picked up a slight magnetic" charge.

Is that true?

Are there simple NDT methods to determine if a stainless alloy is 304
or 316?
Bob

SS hose clips are not necessarily better than zinc plated ones. They
will still look fantastically shiny on the outside, meanwhile
underneath they are about to fail due to crevice corrosion. ZP ones at
least get rusty all over when they are getting old.

I think that both alloys can be made magnetic and may be magnetic unless
they are annealed after working. I am just guessing but polishing should
not cause magnetism. You could have parts that are 304 or 316 that have
become magnetically sensitive by forming and not being annealed afterward.
Both 304 and 316 have similar Fe content ( 65%+). Also guessing, 300 series
ss that exhibits magenetism might tend to spot with rust stains if magnetic?
In out area there are labs that can verify the alloy for not too much $.
Look in your Yellow pages under Laboratories-Testing ,otherwise you'll be
just guessing the actual alloy. If it turned out that it was 316ss and was
magnetic , I don't know how concerned I would be about that? So after my 2
cents you just have more questions, no answer.

--
Ron White
Boat building web address is
www.concentric.net/~knotreel

Bob,

It isn't cheap ($390), but standard test kits are available. See below:

http://www.koslow.com/1499.html

Keith Hughes

Bob wrote:

I received two 7x15 stainless ports today. When I ordered them I was
assured they were 316 ss. So today I thought I would see if a magnet
would stick on one. The magnet stuck. When I called the supplier about
another issue I mentioned that my magnet was sticking to the 316 ss
port. I was told the polishing process was to blame and the 316 had
"picked up a slight magnetic" charge.

Is that true?

Are there simple NDT methods to determine if a stainless alloy is 304
or 316?
Bob

On 2006-01-21 16:29:42 +0100, Keith Hughes said:

Bob,

It isn't cheap ($390), but standard test kits are available. See below:

http://www.koslow.com/1499.html

Keith Hughes

Bob wrote:

I received two 7x15 stainless ports today. When I ordered them I was
assured they were 316 ss. So today I thought I would see if a magnet
would stick on one. The magnet stuck. When I called the supplier about
another issue I mentioned that my magnet was sticking to the 316 ss
port. I was told the polishing process was to blame and the 316 had
"picked up a slight magnetic" charge.

Is that true?

Are there simple NDT methods to determine if a stainless alloy is 304
or 316?
Bob

Hey man why dont you just get out there in your boat and see if she sinks.
I am not being sarcastic sail the damn thing thats what its for!

Jules, Jules, Jules, ..... you don't understand. If we wanted a boat to
sail, we'd buy one of the many used ones available. It's cheaper and much
faster. We build because we want one done our way and we enjoy the process.

Roger

http://home.insightbb.com/~derbyrm

Julesverne wrote in message
...

snip

Hey man why don't you just get out there in your boat and see if she
sinks. I am not being sarcastic sail the damn thing thats what its for!

Hey man why dont you just get out there in your boat and see if she
sinks.
I am not being sarcastic sail the damn thing thats what its for!

Hey Jules:

Thanks for the advice. Before I go sailing I may want to plug the two
7x15 holes in my cockpit first. Most of us in the northwest tend to
avoid "free commnication with the sea."

Oh, I almost forgot................ GFY.
Bob