[opendtv] Re: Steel pipes for gas!
- From: John Willkie <johnwillkie@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 31 Oct 2006 13:04:21 -0800 (GMT-08:00)
I think that it's very much simpler to find a steel gas line using simple
technology than to find a plastic gas line.
John has a point about steel being more rigid than plastic (I was wondering
when that would come up), but it depends on the nature of the threat. Having
been through more than a few earthquakes (but never severly affected), I think
I like rigid. If a fissure opens in your front yard, I don't think it matters
much the form of the gas pipe. Fissures in front yards are somewhat rare.
As to steel corrosion, that is a factor of the conductivity of the soil and
other soil conditions like moisture content. The steel water mains that were
laid in San Diego in the late 1880's and early 1900's generally have 30-50 life
spans. We have thousands of miles of them, and they do give from time to time,
a problem that the city identified in the late 1970's, but has ignored.
Instead of replacing many, they just repair the many breaches. Some sections
of pipe, with good drainage, appear to last for more than 100 years. Others,
with bad drainage, seem to burst all the time. The city stopped permitting
steel and iron water mains about 50 years ago.
Last I heard, all new water mains were AC (asbestos concrete) with 75-100 year
life spans. That's probably been changed in the last few decades.
The real advantage of steel gas mains for broadband is the lack of a need to
coordinate frequency usage. Think of cable with a bigger shield.
John
-----Original Message-----
>From: Craig Birkmaier <craig@xxxxxxxxx>
>Sent: Oct 31, 2006 4:52 AM
>To: opendtv@xxxxxxxxxxxxx
>Subject: [opendtv] Re: Steel pipes for gas!
>
>At 5:24 PM -0800 10/30/06, John Willkie wrote:
>>We know that gas lines break during earthquakes (Northridge '94,
>>magnitude 7.1), and although it's been a few decades, I remember
>>attending San Diego City Council meetings where building code
>>upgrades were discussed, including keeping the requirement for steel
>>gas lines. Haven't paid much attention since then.
>
>Hmmmm...
>
>If I were concerned about the potential of breaking a gas line, I
>would probably prefer the plastic lines now being installed. There
>are three general problems that can cause gas leaks:
>
>1. Construction crews that do not properly locate utilities before
>digging. We've had two such incidents with gas lines in the past year
>or two here in Gainesville. I doubt that steel has any advantage over
>plastic when a back-hoe snags a line.
>
>2. Corrosion. Plastic is the hands down winner here. The
>installation procedure uses ultrasonic welding techniques, which make
>the joints as strong or stronger than the plastic pipe.
>
>3. Earthquakes, sinkholes, etc. When the ground starts to shift,
>which would you rather have, a pipe system that is flexible and can
>bend, or one that is rigid? We are not talking about plastic water
>mains or sewer pipes, which typically have segments that plug-in to
>one another with gaskets or glue. Gas mains are thick wall plastic
>with ultrasonic welds.
>
>Regards
>Craig
>
>
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