Magnetic 316 wire
 

I have some new rigging on a boat which is supposed to be 316 but it is moderately attracted by a magnet and some individual strands are showing surface corrosion throughout the length of the stays.

Anybody come across this or got any clues?:confused:

It shouldn't
 

Hello,
While it is possible for 316 to be, or to become somewhat magnetic, doing so involves either complex or crappy metallurgy. Most likely the latter. You might simply be seeing the results of a little bit of impurities, but no way of knowing. Since you are paying for 316, and since it is supposed to be austenitic, it really should be non-magnetic.
Fair leads,
Brion Toss

Thanks Brion, That is what I suspected.

316 mildly magnetic
 

316ss can be made mildly magnetic by cold work. This happens in wire drawing. The corrosion spots can be contaminates from the drawing die. As Brion suggest the presences of rust spots could also be due to excessive inclusions (crap). On way to check the wire you have is ask vendor for production lot chemistry report and compare to ASTM specifications. Hope this helps some.

Goodwinds
DaveM

Barber Pole Look
 

Ahoy John ,,, getting good quality wire is harder than you think .

Each batch of raw wire before it is wound into 1 X 19 , can be suspect .

If you have only one outside strand showing corrosion , ( I think it is called , "Barber Pole" ) ,,, like rust corrosion , would you open up the strands to inspect the core wound wires , too , or would you assume that there may also be a corroded wire in the core windings , as well ?

I found that Barber Pole rusting effect on my 316 SS 1 X 19 rigging wire , too , but cleaning the outside with pickling paste (nitric / hydrofluoric/ phosphoric acid combos) that cleaning did not go into the core wires,,,,, eventhough the cable looked fine , ie: bright and no rust , on the outside ,,,, later I found out the inside core wires were v rusted , Ouch !

There is v good reason that knowledgable surveyors recommend to replace all SS structural fittings after 10 years , use , in warm salt water environments .

The Mill Certificates from the Chinese supplier show it is 316. We are going to send off samples for chemical analysis. I guess if that comes back normal the client will have to accept it.

Chemical Analysis Yourself
 

Ahoy John ,,, the difference between 304 SS and 316 SS , is , a small amount of Molybedum (sp-?) 2% or so , is added , to reduce rust pitting of the 316 SS .

I did find on internet searches , that SS can be tested chemically , to determine if it is 304 or 316 , and that can be identified .

The test suggests to use Hydrochorlic acid drops on the SS sample ,,, as that acid reacts with the molybedum ,,, if it shows present ,,, it is 316 , if not it will most likely be 304 , which in warm water salt water environments , show rusting then pitting corrosion on your 304 SS , heaps faster than with 316 .

It is hard to find useful info on SS ,,, you have to look in many places .

I have been told that SS from China , is not always up to Mil Spec or ISO standards ,,, but that Korean SS is more reliable . The bulk of our wire comes from either place , or so I am told !

Try this website for metal testing kits : http://sfiaust.com.au/search_results...-moly-drop-960 ,,, or this one ,,,,, http://www.koslow.com/metal_test_kits/1542c.html

BTW we purchased our new 316 SS 1 X 19 , in Phuket , from an Aussie owned shop , that inported all his wire from Oz ,,,, the printing on the spool said Sta-Lok , and Arcos (from Oz) and now less than a year in Singapore , we have "barber pole" rust showing up on one outside strand , Drats !

Results
 

Hi again,
I look forward to seeing the results of those tests. Be sure to keep us posted.
Fair leads,
Brion Toss

The yard (and their lawyer...) were presented with the evidence and have agreed to replace the faulty rigging regardless of the outcome of chemical testing. I will try to get the test results once they are done. Thanks for all the advice.