"Ignoramus21697" wrote in message
...
On 2010-12-14, Steve B wrote:

"Erik" wrote in message
...
Hi all,

Sorry for the long URL.

http://latimesblogs.latimes.com/lano...sections-of-se
am-on-exploding-san-bruno-pipeline-were-welded-only-on-outside.html

Erik

I copied and pasted this url, and it worked for me. The second one you
posted said OOPS, broken.

This is interesting.

VERY FEW pipelines are welded both inside and outside. Most are just
welded
on the outside, that being a confusing term. They are welded FROM the
outside, but the root pass penetrates into the inside of the pipe a tiny
bit, and joins the root of the two pieces together. Very few pipelines
are
welded on the inside because it interferes with the cleaning devices run
through them. That would be for the welds that join the two pieces of
pipe
together.

The article was about the absence of longitudinal welds, that is the
welds
running from end to end, made when the pipe was rolled into a tube, and
the
edges joined along their two longitudinal edges. The welds are then
finished so fine that it is difficult to find the weld. Apparently, the
sections of pipe had longitudinal welds that had inside and outside
welding,
but some were missing the internal half of the weld. There would be
major
inconsistencies if they were present in some sections, and not in others,
or
were intermittent, as from a malfunctioning welding machine. I would
suggest that they were made with an automated welding device, perhaps
using
the SAW technique. (Submerged Arc Welding)

It will be interesting to follow this. This particular fact of the
investigation is one that I would have never guessed. I always said I'd
wait for the final report, and this isn't even the final report, but it
DOES
provide some of the actual facts of the metallurgical forensic
investigation.


Steve, this is very useful to know. DO you know if that one "outside"
weld that leaves a root inside, is done with one pass?

i

No, I really don't. What I find fascinating is inspecting small square or
rectangular tubing. A welding crown is clearly visible on the inside, but
how in the world do they get it in such a small space? I'd like to see it
on How It's Made, or go to a factory for a tour.

Steve