Posts: 1332
Threads: 53
Registered: July 25th, 2009
Member Is Offline
Location: Sydney
Theme: UltimaBB Pro Blue ( Default )
Mood: Getting hands dirty stripping the bug down
posted on December 9th, 2012 at 07:51 PM
Just to clear up one point surgical stainless is 316L,the "L" indicating low carbon.
nils
Fahrvergnugen
Posts: 971
Threads: 65
Registered: January 11th, 2008
Member Is Offline
Location: central coast
Theme: UltimaBB Pro Blue ( Default )
posted on December 10th, 2012 at 05:04 AM
Now THAT makes sense to me, thanks for that bit of info peter.
Quote:
Originally
posted by modulus
When 304 and 316 grade stainless steels are held at elevated temperatures for long periods (say 500C for 100 hrs or so), the crystalline structure can
change to a form referred to as "martensitic". This structure is much more brittle than the original and can lead to cracking failures which are
sometimes experienced in e.g. oil refinery column trays which operate under exactly these conditions.
If a 304/316 stainless exhaust is of adequate thickness and properly supported, it would be unlikely to experience such a failure in a reasonable
exhaust lifetime; however, some systems are made of very light materials and (especially on air-cooled VWs) are poorly supported. In such
circumstances, martensitic embrittlement failures would be expected.
I have no experience testing 409 grade SS, so I don't know how that grade would react to long-term elevated temperatures. No direct equivalent
embrittlement process exists for mild carbon steeels, though as noted by other posters it is prone to rusting, which will determine the effective
lifetime of a carbon steel exhaust earlier than anything else.
A decent quality stainless or carbon steel system will give an acceptable lifetime if properly supported, and *that* is the big issue with air-cooled
VWs, of far more importance than the choice between SS and CS.
