On Tue, 14 Dec 2010 21:15:02 -0600, Ignoramus21697
wrote:

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

Certainly. I visited a pipe plant in W. Java that made spiral welded
pipe ranging from 12 inch to 36 inch, with a maximum capacity of 48
inch. An Australian based company had built the plant and were in the
start up phases when I was there. All of their pipe was welded single
pass using a submerged arc system.

You could see the weld on both the inside and the outside and as I
recollect that was the first stage in inspection - look to see if it
was a continuous weld on both sides.
Cheers,

John D. Slocomb
(jdslocombatgmail)