On July 2, 2017, at 12:32 p.m. eastern standard time, a natural gas explosion and fire destroyed a single-family residence at 206 Springdale Lane, in Millersville, Pennsylvania. One person died, and three people were injured. Two nearby residences were severely damaged and condemned for demolition.
UGI Utilities, Inc. (UGI) supplied natural gas to the Millersville residences through a plastic natural gas pipeline (main) and service lines, which UGI operated at a pressure of 54 pounds per square inch, gauge. The main was 2 inches in diameter and made of Aldyl polyethylene; the 0.50-inch diameter service lines were made of polyethylene. Post-accident, the main and service lines at the accident site were pressure tested, which indicated that a PermaLock mechanical tapping tee assembly was leaking gas at the connection of the tee assembly to the main in front of the destroyed residence. UGI installed the tee assembly in June 1998; it had been in service for 19 years when the accident occurred.
The NTSB examination of the PermaLock tee assembly involved in the accident has revealed that the tee assembly was incorrectly installed. Although the cutter tool pierced a hole in the main, the locking sleeve did not progress down far enough into the tower to form threads in that hole. As a result, the locking sleeve was not attached to the main. The NTSB also found that two of the four Nylon bolts on the tee assembly were fractured in a manner consistent with slow crack growth. These findings indicate the likelihood of varying tee assembly installation techniques.
On June 25, the NTSB issued the following recommendations:
To the Pipeline and Hazardous Materials Safety Administration:
Work with state pipeline regulators to incorporate into their inspection programs, a review to ensure that gas distribution pipeline operators are using best practices recommended by the manufacturer in their distribution integrity management programs, including using the specified tools and methods, to correctly install PermaLock mechanical tapping tee assemblies. (P-18-1)
Reference the use of external sources of information for threat identification in your frequently asked questions for preparation of distribution integrity management programs. (P-18-2)
Update your PermaLock mechanical tapping tee assembly installation instructions to specify the exact tools that should be used during installation and explain what an installer should sense while using those tools throughout the installation process. (P-18-3)
Specify in your PermaLock mechanical tapping tee assembly installation instructions a not-to-exceed torque limit for Nylon bolts and have that value checked and adjusted with a torque wrench immediately after installation. (P-18-4)
If you have any questions about the NTSB’s safety recommendations for Installation of Permalock Mechanical Tapping Tee Assemblies, contact Nick Vandegriff, IAMU Gas Services & Compliance Specialist at firstname.lastname@example.org or by phone at 515.289.1999 (office), 641.919.8411 (cell).