By Seth Kovnat
The Pipeline and Hazardous Materials Safety Administration (PHMSA), which is the federal agency tasked with pipeline safety inspections, recently issued a Notice of Probable Violation to Sunoco concerning pipe damage during “field bending” last March. In this guest blog post, Seth Kovnat explains the engineering issues involved in field bending and why this violation is so disturbing.
Pipeline bends, often overlooked, are critical in any pipeline. It is not possible for a pipeline to be a straight line, so every pipeline must have bends. Some bends are pre-planned and done in a controlled production facility. Others are made in the field.
Sunoco’s proposed Mariner East 2, designed to carry hazardous and highly volatile liquids, is no different and has many bends, especially as it navigates through our densely populated areas. It is critical that bends are structurally sound as they must take large flow forces and surges in momentum that are caused by the presence of the bend itself. The problems associated with bends, coupled with the inherent hazards of the highly volatile liquids that it is designed to transport, make one recent Mariner East 2 Notice of Probable Violation especially alarming.
Last week, PHMSA issued a Notice of Probable Violation to Sunoco that is directly related to the construction practices it is using for the Mariner East Pipeline. While Sunoco has been cited for many violations at both the state and federal level, this one in particular is very troubling.
“During the inspection, the PHMSA inspector observed pipe being installed in a trench near the Markwest Hopedale Cryogenic Plant off Jewett Hopedale Road near Hopedale, Ohio. Just east of the pipeline installation, pipe segments were strung out in a linear fashion in the pipeline right of way. Upon inspecting the pipe that was strung out, the PHMSA inspector observed numerous coating scrapes on at least 5 segments of pipe. Several segments of pipe had severe coating damage, and at least one joint of pipe had a gouge that extended into the wall of the pipe. Markings on the pipe identified the segments as having been subjected to field bending.“
The problem here has many layers but what it comes down to is:
- Damage to the pipe reduces its strength; and
- Any damage to the protective coating provides a path to accelerated corrosion
That there were “several segments of pipe” with this problem indicates that the problem is likely systemic and not an isolated incident. The fact that Sunoco was in the process of installing this unsatisfactorily finished pipeline means they have probably been installing pipe to this same unsatisfactory standard elsewhere. The fact that Sunoco’s own quality inspector had signed off on the damaged pipe means that similar damage has probably been accepted in other cases. The timing of this probable violation (March 2017) is troubling as it coincides with the very beginning of Mariner East 2 construction. And the fact that this Notice was not issued until just now only increases the likelihood that a lot of pipe already in the ground has been installed with similar defects.
Why the 10-month delay? Part of the reason for the delayed response to this violation is that PHMSA simply doesn’t have enough inspectors to do more than spot-checking paperwork and occasional field inspections. The shortage is so great that each inspector is, on average, responsible for pipeline that is equivalent to the distance from Miami to Seattle. It is unlikely that PHMSA has been able to effectively monitor the construction of Mariner East 2.
And Sunoco has previously been caught cutting corners. Sunoco recently received federal enforcement action for using uncertified welders on another hazardous materials pipeline. That pipeline ruptured not long after going into service, failing “at or near a girth weld”.
Bending damage is just as problematic as improper welds. In fact, it is even more of a concern because while welds receive a lot of attention (in theory at least), bends do not—and damage from the bending process is difficult to inspect.
Big pipes are a big challenge. The type and size of the Mariner East 2 pipe adds significant risk to the bending process. The reasons are as follows:
- Larger diameter pipe is stiffer
- Steel that is heat treated for added strength is less ductile (more susceptible to cracking)
- The thinner wall thickness, made possible by the heat-treated steel, increases the likelihood of buckling and other local damage.
The pre-planned bends in the route are not the problem. These bends are made at a production facility using methods that are designed to protect the pipe. These production bends are “hot-formed”, locally heating the bend site to relax the steel so that it can stretch without buckling or damaging the pipe. After bending, the pipe is heat treated to relax it, a process that not only removes latent stresses that could cause it to spring back but also restores its increased strength properties. At the factory, coating is applied after bends are made, eliminating the risk of coating damage during bending.
The problem of bending in the field. Field bends are a different story entirely. Field bends are made at the construction site. By the time the pipe is at the construction site, it is already coated. Bending pipe on-site risks damaging the coating. Field bends are “cold-formed” meaning that the steel is not relaxed.
- The “cold-forming” process has many consequences that make detailed inspection exceedingly important:A cold pipe requires more force to bend than a hot pipe. “Cold-forming” is therefore much more likely to cause cracks in the coating and buckling in the pipe. This damage can be overlooked (as Sunoco’s inspector did in this case). It is sometimes inspectable (as evidenced by PHMSA’s inspection in this Notice). However, many times the damage is at the microscopic level and is not visible to the naked eye. Corrosion can occur even with the slightest bare steel exposure.
- Since the steel is not heat treated after bending, the pipe retains significant internal stress from the “cold-forming” bending process, far more than in the more gentle “hot-forming” factory bending process. As a result, the pipe will eventually relax on its own by springing back over time. The time required for the pipe to fully relax is measured in days. In projects that are rushed, as ME2 appears to be, sometimes the pipe doesn’t sit long enough and is welded up with adjacent pipe while it is still in a stressed state. Eventually, even after installation, the pipe will relieve itself by springing back. If this occurs, the pipe can literally buckle itself (see image below).
For these reasons and more, field bends are often the cause of pipeline failures and must be fully inspected. The fact that Sunoco was caught in the act of installing pipe with damaged bends is very concerning. The lack of enough PHMSA inspectors to hold Sunoco accountable on every bend means that it is likely there are damaged bends already buried. This needs to be rectified, as the public and PHMSA have now lost all confidence in Sunoco’s credibility.
The public safety risks with highly volatile liquids are too high to risk a leak that can cause mass casualties. Governor Wolf should insist that Sunoco uncover the pipe that is already installed and prove it is satisfactory. Otherwise, we may learn of their deficiencies the hard way—and no one wants that to happen.