MWRA Break Caused by Stud Failure

According to a report released yesterday by the Massachusetts Water Resources Authority (MWRA), a progressive stud failure caused a water main break on May 1, 2010, which affected more than 2 million residents in Massachusetts, including Brookline

The report was authored by an independent panel, comprised of Zorica Pantic, chairman of the panel and President of the Wentworth Institute of Technology; Ronald G. Ballinger, a professor of nuclear science and engineering and material science and engineering at the Massachusetts Institute of Technology; and John H. Bambei, Jr., Chief of Engineering at Denver Water.

The panel wrote that it considered two scenarios, a "vertical displacement" scenario and the progressive stud failure scenario, but dismissed the former, writing "the panel judged the first scenario is not consistent with the evidence retrieved from the break."

The progressive stud failure scenario blames two aspects of the studs: The first, progressively increasing water pressure that exceeded limits for the studs; and the second, questions about the installation of the studs and the effects of rushing water over time that affected the reliability of the studs.

The report found the problem began with the initial installation of some studs on the main. The studs' initial installation led to some cracks at the thread roots.

At the same time, the studs became overloaded, going over the acceptable limits defined by the American Society of Mechanical Engineers (ASME). The overload led to more cracks and some studs failing, which put even more pressure on the remaining studs.

All this led to complete stud failure, which in turn forced a so-called "blow out" of the O-rings present.

"Once the O-Rings became free, the leak rate—up to this point minimal—increased almost instantaneously to the rate observed," wrote the authors in the report.

Pictures in the report of studs found after the break show them to be rusted and damaged, and the authors write that all of the studs recovered show small cracks at the top and thread roots.

The studs were provided by Victaulic, a pipe system company, and the authors of the report write that not only had the studs come in with pre-existing cracks, the MWRA staff felt the installation process did not go as smoothly as they would have liked.

The authors wrote the installation process for the studs, which was provided to the MWRA staff with a video from Victaulic, is "very specific" and does not mention double-nutting anywhere. Studs that were located after the break were found to be double-nutted.

In addition, "log books describe a stud tightening process that occurred AFTER the initial installation which is allowed by the procedures but would have put an additional, and unknown, load on the studs. All of this suggests that additional load may have been applied to the studs that would not normally have been applied had the installation procedures been followed exactly," wrote the authors.

The Globe reported earlier this month that the MWRA is preparing to sue several companies for the main break.

Victaulic released a statement to the Globe at the time saying that the company has "consistently and openly communicated to the MWRA that the system failed due to multiple factors—factors that were under the planning, control and management of the MWRA."