On June 25, the National Transportation Safety Board (NTSB) issued two safety recommendations each to the Pipeline and Hazardous Materials Safety Administration (PHMSA) and Honeywell regarding Permalocktm mechanical tapping tees. The recommendations stemmed from a July 2, 2017 natural gas explosion and fire that destroyed a single-family residence in Millersville, Penn. One person died, and three people were injured. Two nearby residences were severely damaged and condemned for demolition. Post-accident investigation found that a Permalocktm mechanical tapping tee assembly was leaking gas at the connection of the tee assembly to the main in front of the destroyed residence. The tapping tee had been in service for 19 years when the accident occurred.
Examination of the Permalocktm tee revealed that the tee 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.
On June 25 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 Permalocktm 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)
To Honeywell:
Update your Permalocktm 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 Permalocktm 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 your utility currently installs Permalocktm or similar mechanical tapping tees APGA urges you to ensure that your installation procedures and training for installers include using the correct tools and methods to correctly install these fittings. If you have installed such tees in the past APGA encourages you to take this potential threat into account when you next update your integrity management plan. The APGA Security and Integrity Foundation will revise its Simple, Handy, Risk-based Integrity Management Plan (SHRIMP) program to include this threat.
The full NTSB report can be found on the APGA website. For questions on this article, please contact John Erickson of APGA staff by phone at 202-464-0834 or by email at
jerickson@apga.org.