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W6KWF > TECH 30.09.21 07:30l 52 Lines 3020 Bytes #999 (0) @ WW
BID : 2455_N0ARY
Read: GUEST
Subj: Scattergood-Olympic Line 4/7
Path: IW8PGT<LU4ECL<HR1PAQ<CX2SA<N6RME<N0ARY
Sent: <10930/0231 2455@N0ARY.#NCA.CA.USA.NOAM [San Jose, CA] $2455_N0ARY
Every vault also has a nipple which allows sampling of the pipe oil.
They said you withdraw the oil through a thick membrane with a syringe
(?). This happens monthly on all feeders in the LA area. The samples are
analyzed downtown by a staff of chemists who can relate the presence of
things like acetylene, butane, and benzene in the oil to arcing,
coronas, and so forth. Apparently the oil chemistry is a very good
indicator of the health of the segments.
One of their worst fears, after they open up the pipe, is having a
blowout of the freeze plugs. If they ever run out of nitrogen during the
repair process they'll lose one side of the pipe (or both). Right now
they've got the pipe on each side of the fault dropped down to 80 PSI.
They are afraid that if they go any lower in oil pressure any gas in the
oil will come out of solution and cause an explosive expansion. Not only
that, but since there is so much oil embedded in the paper insulation,
any sort of gas bubbling (oil foaming) would shred the insulation,
rendering the entire feeder useless. They say it could take months to
safely let the pressure off to zero. (That is the other reason ($13k/hr)
they cannot afford to drain the whole pipe.)
Even at 80 PSI, if they lose a freeze plug they will have a really big
mess outside the pipeline. The holes they've dug cannot hold 100K
gallons and they're operating on a hill near the beach anyway... (Big
pollution threat for LA basin.) Potentially fatal for anyone around.
Right now they have LN-2 companies on call from San Diego to San
Francisco with contingency plans of all sorts in case there is a major
traffic problem with trucks getting in.
They say the repair could take weeks or more, depending on what they
find when they get inside. They believe the cause of the fault was the
inner conductors slipping downhill inside the pipe and shorting against
a metal flange. Even if that's true they wonder where it slipped to, and
hence, where it may be bunched up down hill.
Finding the fault was a problem in itself. Since this was all new to
them they really didn't know how to start. They tried time-domain
reflectometry equipment but got inconclusive information. They tried
ultrasound and radar but that didn't work. Then they got a thing called
a "thumper" shipped in which got them pretty close. The thumper sends
mondo-amp pulses into one end of the cable. The electromotive force
tends to cause physical displacement of the conductors which you can
hear from the street level. The place where the clicking stops is where
the problem usually is. This got them to the defective segment.
What pinpointed the problem in the end was a bunch of car batteries and
some millivoltmeters. (From one technology extreme to the other.) They
hooked up car batteries to both ends, tapped the cable at several points
(maybe there are taps in the vaults?) and, knowing the drops and
resistance of the cable, got within a few feet of the fault. (I used to
use the exact same technique on memory boards.)
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