Date:         Thu, 22 Apr 2010 02:19:39 -0500
Reply-To:     Tom Hargrave <thargrav@HIWAAY.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tom Hargrave <thargrav@HIWAAY.NET>
Subject:      Re: Hose clamps..
Comments: To: David Beierl <dbeierl@ATTGLOBAL.NET>
In-Reply-To:  <4bcf3cc8.9453f10a.7911.69cf@mx.google.com>
Content-Type: text/plain; charset="iso-8859-1"

Stainless is made corrosion resistant by a thin oxidation layer on the
surface of the metal called passivation. Spot welding will destroy the oxide
layer protecting the SS from rust but it takes very little time, literally
seconds, for the weld area to re-passivate and protect the welded area from
corrosion.

The real issue is not "is the clamp spot welded", but what series stainless
steel is it made from? Good stainless steel clamps should be made of 304
series stainless steel.

From http://www.ssina.com/faq/index.html#6 web site:
"When the amount of chromium (in an iron matrix) exceeds 10 ½%, a complex
chrome oxide forms instantaneously that prevents the further diffusion of
oxygen into the surface and results in the "passive" nature of stainless
steel and its resistance to oxidation (or corrosion). A chemical "dip" into
10% nitric acid plus 2% hydrofluoric acid bath will enhance the development
of this "passive" oxide."


Tom
www.kegkits.com


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
David Beierl
Sent: Wednesday, April 21, 2010 12:53 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Hose clamps..

At 10:28 AM 4/21/2010, Don Hanson wrote:
>Besides having SS for all the parts, the marine clamps are a usually a 
>magnitude better built..but more costly, of course.

Two things to watch out for in SS clamps: first, is the screw also SS?
Second, is the clamp housing folded/crimped onto the band, or spot welded?
Spot welding destroys the rust resistance in that area and the clamp can and
does abruptly fail at the weld with no previous warning since the weld is
invisible when the clamp is installed.  Both issues are less likely in
clamps from a chandlery vs a FLAPS.

Yours,
David