The Texas Railroad Commission (TRRC), Safety Division, initiated a study into the use of compression couplings in natural gas distribution systems as a result of three incidents involving mechanical type compression couplings. In addition to the recent incidents in Texas, there is history within other states of significant incidents related to coupling failures.
While the leading cause of incidents in Texas is third party damage (77%), these recent incidents involving compression couplings has raised the level of concern. Each of the incidents involved different type couplings and different operational characteristics, yet they all involved compression type couplings that were installed more than twenty years ago. Of specific concern is the continued safe operation of natural gas distribution systems that contain compression type couplings. While there have been improvements in materials and manufacturing methods over the years, the basic design concept has not changed. The applicable sections that cover the installation of mechanical type couplings are found in 49 CFR Part 192, with specific sections §§192.161 (e), 192.281, 192.283, 192.285, and 192.287.
In researching the use of compression couplings across the U.S., two prevailing types of failures of compression couplings were identified: pullout of pipe from a compression coupling, and leakage through the sealing surface between the coupling and the pipe. It also may be important to consider other contributing factors can lead to incidents. With the requirement for distribution integrity management (DIMP) expected within this calendar year, it is important to review the operating history of distribution pipelines. PHMSA is looking at how DIMP can help to identify leading and lagging indicators, and what actions PHMSA and the States can take to help assure DIMP effectiveness. No previous or present PHMSA Research and Development is directly addressing the coupling issue. The Safety Division staff has been in contact with the NTSB during the course of the study. PHMSA and NTSB have also met to discuss this issue.
On October 9, 2007, TRRC adopted the first directive as a result of this study. The directive required all operators that find compression couplings leaking to replace the coupling or repair the coupling by welding over a protective sleeve. TRRC is working on a rule proposal to require all pipeline operators to report all repaired leaks on their pipeline system. The report will include information on the type of leak, the cause of the leak, and the leak repair method.
In November 2007, TRRC approved a rulemaking to address two of three recommendations, and adopted the third as a directive:
- The first recommendation is for each operator to create a risk based model for scheduling and conducting leak surveys of their pipeline system based on established risk factors. The leak survey model suggested as part of this rule will go in hand with the DIMP rules being developed by the federal Office of Pipeline Safety.
- The second recommendation was a leak grading and repair proposal. This second proposal provides a consistent application of what a “graded” leak is in Texas.
- The third recommendation involves the replacement of certain compression couplings.
For a complete copy of the report, including TRRC’s path forward, contact Jessica Roger.