The Department of Transportation (DOT) has issued an advisory warning owners and operators of natural gas and hazardous liquid pipelines of the potential that high-grade line pipe used in recent projects may have been substandard.
"During pipeline construction in the late fall of 2008, several recently installed natural gas transmission pipeline systems experienced field hydrostatic test failures or excessively expanded pipe joints of large-diameter, microalloyed high-grade line pipe. Metallurgical, mechanical and chemical composition tests of the line pipe in these cases have shown pipe to have yield strengths, tensile strengths and/or chemical compositions that did not meet the requirements of the American Petroleum Institute [API]," the DOT's Pipeline and Hazardous Material Safety Administration (PHMSA) said in the advisory, which was published in the Federal Register Thursday.
"PHMSA was made aware that some of the line pipe that was installed in these projects had yield strengths that were up to 15% below the listed API 5L specification requirements for the specific pipe grade," the agency said.
"Pipeline owners and operators should closely review the manufacturing procedure specifications for the production and rolling of the steel plate or coil that is to be used in the production of new microalloyed high-strength line pipeline to ensure that pipe steel was properly rolled into steel plate or coil prior to the pipe mill rolling process."
Owners and operators also "should request detailed manufacturing procedure specifications from the pipe manufacturers as a basis for ensuring that critical steel processing parameters such as the detailed rolling schedule [rolling temperature, heating temperature and temperature uniformity] are controlled throughout the steel rolling process," the PHMSA said.
The PHMSA advised owners and operators of in-service pipelines to conduct thorough examinations to ensure that inconsistent mechanical and chemical properties are not inherent in microalloyed line pipe grades on all API 5L--PSL 2, X70 and X80 line pipe installed in recent construction projects.
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