The Pennsylvania Public Utility Commission (PUC) recently wrapped up its investigation of an April 2017 leak of the Dragonpipe (Mariner East pipeline system) near Morgantown, PA. They concluded that a stretch of Mariner East 1 had rusted through, causing it to leak ethane and propane. If a local resident hadn’t spotted it bubbling up from the ground and sounded the alarm, someone could easily have been killed.

The Morgantown leak raises two critical questions:

  • How did it happen?
  • Can the same thing happen elsewhere along the pipeline?

The answer to the first question is “corrosion” (the pipe had rusted completely through). This was documented by the PUC, and I have summarized their findings here.

The answer to the second question is probably “yes, it could happen at almost any point along the pipeline,” and the PUC’s complaint against Sunoco provides the reasons for that answer. To quote the complaint: “[The PUC] alleges that there is a statewide concern with [Sunoco’s] corrosion control program and the soundness of [Sunoco’s] engineering practices….”

corroded pipe
An example of pipeline corrosion (not Mariner East). The corrosion of this pipe occurred in spite of the “cathodic protection” that was supposed to prevent it. From:

In this blog post, I will briefly describe three of the main reasons for the PUC’s concern. There are many more than three: the PUC found a total of 45 violations in its review of the Morgantown incident, and you can read about them by following the links in the preceding paragraph. Here, though, I will be focusing on just three. Two of them have to do with rust prevention.

Did Sunoco ignore its own maintenance plan? Sunoco is required to have a plan for keeping its pipelines in good condition. It is called an “Integrity Management Plan”, and Sunoco likes to mention it when telling the public how safe its operations are. I have not seen it—it has never been made public—but I am willing to assume for the purposes of this blog post that it is a good plan, at least on paper; but if so, Sunoco is not following it.

What we do know about the plan is that it depends on a technology called “cathodic protection” to keep its pipes from corroding. This technology involves making sure there is a small but steady electrical current flowing to the pipeline from the surrounding soil. I have provided a more detailed explanation of cathodic protection here, but for now there are only two important facts to bear in mind: the pipeline needs to be maintained at a specific voltage (at least -850 millivolts), and the current must flow toward the pipe, not away from it. If those criteria aren’t met, the pipeline is not protected.

In fact, the PUC found that Sunoco failed to meet those two criteria, and it also ignored another glaring indicator of a problem. These were all logged in Sunoco’s own records:

  • Sunoco was failing to maintain the right voltage, and knew it. Because of the chemistry involved in rust formation, the pipeline has to have a negative voltage of at least -850 millivolts for cathodic protection to work. Any less, and corrosion continues. According to Sunoco’s own records, the voltage of the pipeline near Morgantown was -628 millivolts in 2016 and -739 millivolts in 2017—insufficient to prevent rust in both cases.
  • Sunoco was failing to ensure that the current was actually flowing toward the pipeline, and knew it. The current flow can be disrupted by various factors, such as neighboring pipelines and overhead power lines. According to Sunoco’s own records, there were several locations near the Morgantown leak where the current was flowing away from the pipeline, not toward it. That meant the pipeline was not protected.
  • Sunoco knew that the pipeline was thinning, and failed to do anything about it. Although proper cathodic protection should keep pipes from corroding, pipeline companies still need confirmation that it is actually working. They periodically send an in-line inspection tool (a “smart pig” in industry parlance) through their pipelines. The smart pig uses a magnetic field to detect variations in the thickness of the pipeline wall. It can’t detect small cracks, but it can signal major problems, such as an area of significant corrosion. Sunoco sent one through the pipeline in early 2017, and it showed thinning of the metal in the Morgantown area. That should have been a serious warning signal.

Each of these three issues is a significant problem that should have triggered immediate corrective action by Sunoco. I assume that Sunoco’s Integrity Management Plan contained instructions for dealing with each of them. But if you want a plan to work, you have to make sure it gets followed. Sunoco failed to do that, and a potentially deadly leak resulted.

Mariner East 1 is probably rusting everywhere. If these issues happened at Morgantown, where else might they be happening? The PUC didn’t look at data for the rest of the pipeline, but there is every reason to suppose that if Sunoco is negligent in its maintenance in one location, it will be negligent elsewhere. There is probably serious rust at many points across the state. That’s why the PUC expresses “statewide concern with Sunoco’s corrosion control program” and why it asked Sunoco to propose a retirement date for Mariner East 1.

All across the state, Mariner East 1 is currently carrying highly explosive, highly volatile liquids at high pressure. And all across the state, more than likely, the pipe is gradually rusting out. Thousands of people are at risk. Sunoco tells us not to worry; everything is fine. That’s exactly what they said before the Morgantown leak.