[C320-list] You guys are killing me!

[Stephen Cox]

> 
> Not sure I follow this discussion. Aren't the vinyl coated 
> lifelines stainless? I know that certain rules require that 
> the stainless be uncovered so that rust, etc. can be seen, 
> but the lifelines are otherwise identical . I thought the 
> real choice now was between metal (covered or uncovered) and 
> synthetic cord lines. 
> 

The covered stainless lines may well be a different grade stainless to
straight stainless lines.  The real issue is corrosion under the covering.
See this extract from http://www.vmrgladstone.org.au/metals.html, on
particular the last paragraph (Bolding added by me).


	What is Marine Stainless Steel?
	Marine stainless is composed primarily of iron (at least 50%), with
chromium (10%) and nickel added. Once exposed to the elements, the chromium
enables the alloy to form a tough oxide film and thus gives stainless steel
its unique resistance to rust. Marine grade lies within the 300 series and
for most boating applications, that means grade 304 and 316. The difference
between these two is the proportions of other elements added to the basic
iron.
	Grade 304. Is generally used for fasteners, rigging and fittings. It
is sometimes referred to as 18-8 because it's made by adding 18% chromium
and 8% nickel.
	Grade. 316.contains more nickel than 304, and 2% molybdenum. It is
the most corrosion-resistant of standard stainless steels, is more
expensive, and has about 85% the strength of grade 304.
	Finding increasing use in marine work, particularly for forming and
bending, is Grade 445M2, which has equal corrosion resistance to gr. 316 but
costs less. 

	Weak Points
	1. Crevice Corrosion. Stainless steel normally remains corrosion
free because the chromium in it oxidises (reacts with the oxygen in the
atmosphere) to form an inert skin that protects the metal. If stainless
steel is deprived of oxygen a destructive process called crevice corrosion
will soon begin and it can occur above the water line. Rust stains are a
sure sign. Stainless fastenings holding sea-cocks, struts or shaft logs
should be closely watched. Common problem areas are anywhere there is wet
wood or fibreglass, or there are stainless plumbing fittings that hold or
deliver sea water.
	2. Welding Stainless Steel.
	Weld migration, weld decay or carbide precipitation are all terms
describing failure when stainless steel is welded. It occurs when heat
drives certain elements out of the alloy adjacent to the weld bead, leaving
	a 1-2 mm, strip of mild steel along either side of the weld.
Obviously a weld is only as strong as the metal surrounding it, so be
cautious when welding stainless of unknown stock. Suitable product for
welding should include the suffix 'L' (e.g. 304 L or 316 Q meaning it has
low carbon content.
	
	Guarding against crevice corrosion within PVC jacketed stainless
steel lifeline is an important safety consideration. Brown staining around
the swaged end fitting is a classic sign that water has migrated between the
wire and the plastic cover. Once there in this oxygen depleted area,
corrosion sets in quickly by breaking down the oxide film on the wire and
swaged fitting. In this state, the integrity of the boat's entire lifeline
system is questionable. This is why the Australian Yachting Federation has
banned PVC jacketed lifelines. 

Hope this clarifies things, 


Stephen Cox
Tegwen #1141