Question of the week:
A fairly large, 24 inch I believe, natural gas transmission pipeline recently failed here in Pennsylvania, and I was surprised that it did not ignite. I thought when natural gas pipelines ruptured they normally catch fire. Can you tell me why this one didn’t?
I think you are referring to the recent William’s Transco failure in Lycoming County, Pennsylvania that is described in a newspaper account here. We can’t really tell you why that one did not ignite, because few specifics are known about that failure at this time, but it is not unusual for gas transmission pipeline to rupture or leak without igniting. It all really depends whether the gas coming out finds an ignition source, which normally in an open area such as where this rupture occurred would be from sparks from the pipeline and rocks flying around due to the pressure of the escaping gas, or even static caused by the rapidly escaping gas.
We took a quick look at all the significant natural gas transmission pipeline incidents in the past 5 years and came up with this graph that shows for the various types of pipeline incidents whether they ignited or not. As you can see more often than not pipelines do not ignite when there are incidents, even when the lines completely rupture. We suspect that part of the reason people think they ignite more often is that when they do the incidents are quite spectacular and tend to make the news, whereas when they don’t ignite people hear much less about them.
It is not unusual for these types of gas transmission pipelines to be operating at 800-1000 psi or more. Compare that to your car tires that operate at 30-35 psi and you get a sense of how much pressure is in these pipelines. Even just the pressure of the gas escaping can cause some impressive damage as the picture below shows. This picture shows a similar pipeline rupture in Washington State where there was no ignition. The crater is just from the force of the gas escaping. Notice the piece of pipe in the upper right hand corner of the picture. That is how far the force of the escaping gas threw that piece of heavy pipe.
Hope that helps answer your question.