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Gas Explosion is the worst I have ever seen

in my 50 + years:

1. Huge gas-line explosion rips through San Francisco suburb
    YouTube/The Associated PressA huge fireball erupted in a San Francisco suburb Thursday night, destroying nearly 40 homes by one count and killing at least four people. The explosion, which triggered a fireball that filled an entire street, was apparently caused by a ruptured high-pressure natural gas line operated by Pacific Gas and Electric, although company officials cautioned that the cause of the blaze hadn't been determined. [u][color=#0000ff]The New York Times (free registration)/The Bay Citizen (San Francisco)[/color][/u] (9/10) , [u][color=#0000ff]Google/The Associated Press[/color][/u] (9/10) , [u][color=#0000ff]YouTube/The Associated Press[/color][/u] (9/10)

Today they stated that a weld may have come apart. very unusual as all welds on a 1,000 lb pressure transmission lines are x-ray tested at time of welding.

Someone Smelled Gas?

The way the earth shift in that region of the U.S. I wouldn't be surprized if the pipe ripped from earth quake movement. i thought I heard somewhere where someone mentioned smelling gas hours before ignition. Hmm?

There has also been a mention

of some sewer work having been done in the area. I am sure when all this settles down they will come up with a cause. The NTSB handles these investigations along with DOT. That is because gas travels interstate through large high pressure transmission lines. They actually in this case built houses to close to the transmission line.


As you travel you will notice right of ways with electrical transmission lines above ground. In those same areas gas transmission lines are below ground in these so called "right of ways". Most states have strict requirements as to how close you can build to these and even for farmers how close they can plant crops.

Many years ago we had a farmer in Mass shear of the top of a blow off on one of these lines fortunately it did not cause any explosion or fire just scared the farmer half to death.

Here is some more info

• PG&E ordered to inspect all gas lines following California blast
• 
  Regulators have ordered Pacific Gas & Electric to inspect its entire natural gas pipeline network following a huge explosion that ripped through a San Francisco suburb last week, killing at least four people. The instruction came as investigators found unusual welds on a section of pipe in the rubble from the blast, a discovery that could raise questions over PG&E's pre-blast inspection protocols.
• [u][color=#0000ff]The Wall Street Journal[/color][/u] (9/13) , [u][color=#0000ff]Los Angeles Times[/color][/u] (9/12)

Xray

What's the protocol on the welds. I thought the state has a rep xray each weld before signing off.

That is correct all

welds are x-rayed and a number is assigned to each weld and they are kept by the transmission company.

testing is very stringent

as well as the xray procedure the entire line would have been hydrotested as well. As Tim states each weld is recorded on a weld map that includes location and welder that did the procedure. I would also give some consideration to changing ground conditions that can cause corrosion; the weld fill material acts like an anode (gives up ions) and the pipeline acts like a cathode (receives the ions). If the cathodic protection failed then the first failure point is the weld.

Some more information:

• States wait for results of inquiry into San Bruno, Calif., incident
  The natural gas blast in San Bruno, Calif., has raised questions about the safety of other states' gas grids, but regulators say they won't be rushing to order expensive overhauls. Instead, state officials plan to continue regular inspections and wait for the results of an inquiry into the causes of the San Bruno disaster. "Right now, we have a very thorough inspection process, and we'll continue with that," said one pipeline-safety official. [u][color=#0000ff]Yahoo!/The Associated Press[/color][/u] (9/16)

Age

Pipe was installed in 1956. What is protocol for inspection? Pressure test sections? Not feasible to dig it up and inspect it all the way from end to end. What will happen here do you suppose?

All gas lines are

subject to a survey inspection on a pre-determined schedule. In addition this is why odorant is added so that the general public can become part of the survey. If you smell gas you never enter a building and you call the gas company or fire department.

Most piping is also corrosion protected with anodes which are also monitored on a frequent basis to insure the integrity of the piping.

There is no control however over out side construction damaging piping and failing to report the damage.

This particular pipe is also in an area that has frequent earthquake activity so I would hope a more intense survey schedule would be carried out.

When you look at all of the pipe in the ground carrying all kinds of volatile substances we have a fairly good safety record here in North America.

More information

• PG&E gas-line inspection is questioned in explosion's wake
  Pacific Gas and Electric's inspection method for natural gas lines may be faulty, according to experts. California officials have requested data from PG&E on its gas-pipeline network after an explosion in San Bruno. The state wants to eliminate weak spots before another accident occurs. The Sept. 9 line rupture killed four people and ruined at least 37 homes. [u][color=#0000ff]San Francisco Chronicle[/color][/u] (9/18) , [u][color=#0000ff]The Wall Street Journal/Dow Jones Newswires[/color][/u] (9/18) , [u][color=#0000ff]Reuters[/color][/u] (9/18)

The latest information

• California pipeline "unpeeled," says Stanford University expert
  Photos of the failed section of pipeline blamed for the San Bruno, Calif., natural gas explosion suggest that a weak spot along a seam or weld line could have split the pipeline open like a banana peel, experts say. "This pipe basically unpeeled and failed catastrophically," said Stanford University mechanical engineering professor Tom Bowman. There's little sign of corrosion in the photos, another expert said, perhaps suggesting that overpressure might have placed too much strain on the pipe's weld lines. [u][color=#0000ff]San Jose Mercury News (Calif.)[/color][/u] (free registration) (9/30)