Quote:
Originally Posted by Bowdrie
Perhaps I was unclear.
No, the base metal did fine.
It was the welding/welds.
Perhaps poor technique, perhaps wrong choice of filler rod, perhaps choice of shielding gas for the welding, (gas on both sides of the bead as it moves along IS superior,) whatever, (I'm not a welder,) but any sulfuric acid formed attacked the welds, and fuel back then had a lot more sulfur than today's stuff.
"Back in the old days"?
Ok, maybe ancient in the way many might think. 
In the '50s>'60s, although I've seen tanks from Tiawan boats that were built in the '70s that had leaky welds. I'll grant that the Tiawan SS was not always up to par compared to US product.
Anyway, SS tanks got a bad rap for diesel usage, perhaps undeserved, but there was a learning curve.
As an aside, a friend of mine, (pro welder,) runs a welding/fabrication crew on the North Slope, he says they always run gas on both sides of the welds. When they're joining pipe and fittings there is always some gas being bled thru the interior, keep the oxygen away from the molten metal on the back side.
A company up in the PNW, that builds custom tanks does the same, even in aluminum.
When the tanks were built for "Tally Ho", the guy who welded them pointed out that gas was kept on both sides for the welding. |
No, you were perfectly clear. I think it was me that was less clear.
Given the dates you are talking about, then what i was saying applies. I don't
recall exactly when, but I believe it was in the 1990's there advances in the production of stainless steels, especially the austenitic stainless steels. The stainless alloys of 304 and 316 in the time period you are talking about would commonly be 304 or 316 but you had to pay a premium for 304L and 316L. The L designation means a lower carbon content in the base alloy and those were developed precisely for the problem of sensitization occurring in welded structures.
In the '90's (thereabout), smelting techniques had advanced to the point where it was equally easy to produce these alloys with a chemistry to comply with the L designation as not. Hence all
current 304 and 316 stainless is produced such that it can be what is called "dual certified". Within the ASTM standard for the raw material the carbon content requirement is listed as a maximum permitted - hence 304L and 316L carbon levels actually allow that material to be certified as complying with the requirements for 304 or 316 as well as the requirements for 304L and 316L.
There are some subtile repercussions of this base metal processing change, but for the
current discussion the main impact is on welding. The problem of sensitization in the welded joint has been, for all practical purposes, eliminated. Sensitization in the welded joint is the likely reason for the weld chemistry to not have the same
corrosion resistance as the base metal. Of course as you point out, if someone used the wrong welding rod then you can still have a problem but I put that in the category of incorrect welding technique rather than a concern in base material selection.
Sensitization is the term used for the precipitation of chromium carbides along the grain boundaries of the austenite grains within the base metal, most commonly found in the heat affected zone of welded joints. It can also occur for other heat treat related
mistakes but that is also beyond the
scope of this discussion.
As far as your comment on Taiwanese stainless being inferior, there was a short time period -in fact during the years you reference- where there was a problem in the way they handled revert (recycled metal) that did compromise the quality. However that has long been eliminated and stainless alloys produced there for the past several decades is world class product. I only mention this as often this comment comes up and it's really not the case at all today nor has it been in a pretty long time.
dj
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