Bad weld caused San Bruno pipeline explosion?

Whatever it was, there was quite an explosion. According to news reports the pipe line was buried 4 feet deep.

The blast, which erupted just after 6 p.m. on Sept. 9, threw a section of pipe 100 feet away?a section that National Transportation Safety Board investigators said might hold clues to what caused the blast that left a 167-by-26-foot crater.

The 28-foot length of pipe consisted of several smaller segments that were welded together in an unusual configuration. It also contained a long seam that ran the length of the pipe, the NTSB said.

Any air ordinance types that know how big a [fuel/air?] bomb would be required to blow a crater 167 X 26 X 4? foot deep and blast a piece of 30 inch steel pipe 28 feet long over

100 foot? Something rotten here....

Also does anyone know for sure what the line pressure was and how thick the pipe was? Some back of the envelope hoop stress calculations show there was little safety factor at even 600PSIG, if this was indeed 3/8 wall, and particularly if it has been buried for 50 years w/ no anti-corrosion coating/treatment. Was the line pressure recently increased?

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

"Ignoramus478" wrote

Pipeline failures and ruptures mostly start at some weld point, and then like a weak spot in the paper, a tear follows along that. You will notice that all the photos seem to suggest a failure along a joint rather than out in undisturbed metal.

That is what is the problem. There are no real close ups, to show where failures occur in the adjacent metal, and the actual weld metal holds. In a real world, in a real weld, the weld is stronger than the surrounding metal, as proven again and again and again by destructive testing.

Steve

IIRC, high demand does not cause the supplier to increase pressure. The pressure is static.

Steve

fjo.124711$ snipped-for-privacy@en-nntp-08.dc.easynews.com...

Certainly, here in the UK, the pipeline network is used as a variable high pressure storage container ...

Certainly, here in the UK, the pipeline network is used as a variable high pressure storage container ...

reply: Then I did not recall correctly.

Steve

I own some property that has one of these high pressure gas pipeline running along the very back of the property. When talking to the owner of a construction company I had doing some work who happened to have been the town fire chief some years earlier he told me that that pipeline had a blowout a 1/4 mile or so from my property one winter. The gas did not ignite in that case, however the blowout blew open a ~10' crater from just the gas pressure alone.

The pipeline company that dropped the line through the upper end of our fire district has a seminar yearly on what we should do if there is a problem. One of the things they ask every year at the start of the meeting is "So what will you do if you discover a problem with the pipeline in your area?" My usual answer is "Drive like hell the other way....."

They show films of best and worst case stuff along with what we should do in each case. The Va. blast was in the last one I attended. The video they had and the close up shots of the effects from the blast get your attention.

Scrith, perhaps? Hard to find, really hard to weld....& is it DOT-approved?

Traditionally, service lines are 0.5 {yes one half) psi. More recently, they may be 40 psi with a regulator at the meter. In house is still 0.5.

A transmission line such as this is 1000-2000psi.

You can be sure it was there decades before the subdivision. Pipelines stay put; the suburbs grow...

And other schemes.

Further, it would be wrapped to insulate it from ground, and cathodic protection current applied. IOW, there's a DC source, a sacrificial anode, and electroplating. Any place scraped SHOULD be protected by that, at least short term.

Steve -

Remember this is California - the place that refuses to build another power line through a bottle neck and run the wires almost to melting. The sag is measured and then they start to blackout someone.

The gas line from Texas goes through southern Ca. Another line was refused to be allowed to be built - the first one wanted all and more money.

So another line wasn't brought in to help in the usage.

I highly suspect that these local branch lines into a high use area are to small and as you pointed out to old. Some of these areas are power base politics - e.g. don't dig up my street...

So all they can do on electric - raise voltage to get more power through and with gas - raise pressure. The higher pressure fills the local storage tank (those with floating tops) and keeps them filled as needed.

Infrastructure racked by side slips and bending lands must be maintained at all times else failure is to be expected.

Mart>> Just had a thought.

>>

The pipe may have ruptured along the heat-affected zone of a buttweld. The HAZ is typically more brittle and prone to failure than either the base metal or the weld itself. That could leave a pretty clean fracture line right along the toes of that old weld.

>>>

Still not enough zoom to get a good look at the weld or the structural failure zone.

Steve

IMHO, this post by Leo L and earlier post by Erik show considerable insight regarding what may have actually happened. I also previously assumed that a substantial mass accumulation of NG + air mixture that subsequently encountered an ignition source would have been required to result in an "explosion" adequate to eject the pipe section and create the observed crater. In this scenario, if the NG + air mixture was in a confined space (e.g., underground cavity), the "explosion" could have been a detonation, which creates a shock wave and very substantial overpressure. Otherwise, the "explosion" would have been a deflagration, which usually produces a milder overpressure.

But, I have a question for you welding experts: Is welded-seam pipe such as this gas transmission line usually installed (i.e., laid in the trench) seam up or seam down?

If it is seam-down, then perhaps the sequence of events was simply: pressure acting on weakened welded pipe seam causes section of pipe to split along seam (see photos); reaction forces associated with ~375 psi gas (latest PG&E estimate) escaping through rupture forces pipe up through 3 feet of dirt and breaks off at welded joints; huge mass of escaping gas mixes with air, a large region is in flammable range and eventually encounters ignition source (TBD), mixture ignites and flashes back; a huge escaping gas jet fed flame (torch like) persists for over an hour untill PG&E is able to shut off the gas (and it obviously persists somewhat longer as the pressure bleeds down).

Does this make sense?

IMHO, this post by Leo L and earlier post by Erik show considerable insight regarding what may have actually happened. I also previously assumed that a substantial mass accumulation of NG + air mixture that subsequently encountered an ignition source would have been required to result in an "explosion" adequate to eject the pipe section and create the observed crater. In this scenario, if the NG + air mixture was in a confined space (e.g., underground cavity), the "explosion" could have been a detonation, which creates a shock wave and very substantial overpressure. Otherwise, the "explosion" would have been a deflagration, which usually produces a milder overpressure.

But, I have a question for you welding experts: Is welded-seam pipe such as this gas transmission line usually installed (i.e., laid in the trench) seam up or seam down?

If it is seam-down, then perhaps the sequence of events was simply: pressure acting on weakened welded pipe seam causes section of pipe to split along seam (see photos); reaction forces associated with ~375 psi gas (latest PG&E estimate) escaping through rupture forces pipe up through 3 feet of dirt and breaks off at welded joints; huge mass of escaping gas mixes with air, a large region is in flammable range and eventually encounters ignition source (TBD), mixture ignites and flashes back; a huge escaping gas jet fed flame (torch like) persists for over an hour untill PG&E is able to shut off the gas (and it obviously persists somewhat longer as the pressure bleeds down).

Does this make sense?

reply: I am busy and have far far far too many other things to do, so I'll just be lazy and wait for the reports from the people who are actually touching the evidence, examining it, and who know about such things.

I could be spending all that time analyzing fishing.

Steve

I think it does make sense. Except that I suspect more corrosion occurs at the bottom of a gas transmission pipe regardless of where the seam is located.

I can remember my father telling about a part time gas line inspector who was inspecting a gas line on a Sunday. He called in and reported that there was a right smart leak in the pipe. The dispatcher was not sure what the inspector meant by a right smart leak. Was it worth getting a crew out to fix it on a Sunday? Or was it something that could wait until Monday? The inspector kept saying it was a right smart leak and he reckoned they might want to get a crew out there. When the crew arrived at the location of the leak, they found that the leak had blown out three joints of pipe. But there was no fire.

I can not recall how big the pipe was or the pressure, but think it may have been something like a 12 inch pipe and 600 lb pressure.

Dan

"over-oaked" wrote: If it is seam-down, then perhaps the sequence of events was simply: pressure acting on weakened welded pipe seam causes section of pipe to split along seam (see photos); reaction forces associated with ~375 psi gas (latest PG&E estimate) escaping through rupture forces pipe up through 3 feet of dirt and breaks off at welded joints; huge mass of escaping gas mixes with air, a large region is in flammable range and eventually encounters ignition source (TBD), mixture ignites and flashes back; a huge escaping gas jet fed flame (torch like) persists for over an hour untill PG&E is able to shut off the gas (and it obviously persists somewhat longer as the pressure bleeds down). (clip) ^^^^^^^^^^^^^^^^ If my conjecture about leaking water producing an underground cavity us correct, then let me add some thoughts to what you have said here. If water leakage washed away the soil around the gas pipe, it would have left it unsupported, so it would sag under its own weight. This would create bending stress in the pipe shell, superimposed on the hoop stress due to pressure. This combination of stresses would be acting on a pipe which is already near the end of life from corrosion. This could be the reason for the gas leak which many people smelled, and which ultimately led to the explosion.

IOW, it's likely not a coincidence that the leakage happened just where the cavity was.

I find it really hard to understand that PG&E could not turn off the gas. I heard the valve was to close to the fire... But what about the next one.

There should have been one on each end - isolation valves as they call it.

Sounds as if they didn't want to cut off another neighborhood but just burn the gas until the main regulator tank pressure dropped.

If I was there and in charge or semi-so - cut off the far end to cut off the local - get the fire off and then get PG&E re-light the pilots on the ok section.

Now just who will pay for the gas ? - I bet the customers in the long run.

Mart> "over-oaked" wrote: If it is seam-down, then perhaps the sequence of events

My logic says there is some sort of a device that, whenever there is a drastic drop in pressure, which would happen in a rupture, that there are automatic shutoffs on the pipeline.....................? No one needs to "shut it off". Just like happens with an electric grid. When there is something way amiss sensored by the monitors, it just shuts itself off.

Steve

'I was not there', and I have no information to contribute. I have learned to wait for the investigation report before forming an opinion as to the real cause of any incident/accident or of the completeness or reliability of the investigation.

However speculation can sometimes be fun and an interesting exercise, if nothing else it requires us to have an open mind and to resist jumping to conclusions as often times 'things are not what they first appear'.

[snip]

Good luck with that. The people doing the scraping may be unaware that they've nicked it (to a backhoe, it feels like a rock). And some people may not want to admit it. Or be aware of the consequences.

Back in my days with the power company, we'd share a right of way with a number of pipelines. And the off roaders loved the rights of way as well. There were a few places where people had rutted the roads down to the pipes and continued to drive over them until the wrapping was completely gone. To them, its just like crawling their Jeep over a log.