E9-11815. Pipeline Safety: Potential Low and Variable Yield and Tensile Strength and Chemical Composition Properties in High Strength Line Pipe

AGENCY:

Pipeline and Hazardous Materials Safety Administration (PHMSA); DOT.

ACTION:

Notice; Issuance of Advisory Bulletin.

SUMMARY:

PHMSA is issuing an advisory bulletin to owners and operators of natural gas pipeline and hazardous liquid pipeline systems. This bulletin advises pipeline system owners and operators of the potential for high grade line pipe installed on projects to exhibit inconsistent chemical and mechanical properties. Yield strength and tensile strength properties that do not meet the line pipe specification minimums have been reported. This advisory bulletin pertains to microalloyed high strength line pipe grades, generally Grade X-70 and above. PHMSA recently reviewed metallurgical testing results from several recent projects indicating pipe joints produced from plate or coil from the same heat may exhibit variable chemical and mechanical properties by as much as 15% lower than the strength values specified by the pipe manufacturer.

FOR FURTHER INFORMATION CONTACT:

Alan Mayberry by phone at [phone] or by e-mail at [e-mail].

SUPPLEMENTARY INFORMATION:

I. Background

The Federal pipeline safety regulations in 49 CFR Parts 192 and 195 require operators of natural gas transmission, distribution pipeline systems, and hazardous liquids pipeline systems to use pipe manufactured by a listed specification in the design of pipelines in accordance with §§ 192.7, 192.55(a), 192.105, and §§ 195.3, 195.106, and 195.112.

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, Specification for Line Pipe—5L, (API 5L), 43rd edition for the specified pipe grade. API 5L, product specification level (PSL 2), specifies material requirements in Section 6 and inspection and testing standards in Section 9. Even though the pipe supplier provided the pipeline owner or operator with documentation that the pipe that was delivered to the owner met these minimum standards, substandard pipe properties were found in some pipe joints. Specifically, 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.

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 pipe to ensure that pipe steel was properly rolled into steel plate or coil prior to the pipe mill rolling process. Pipeline owners and operators should request detailed manufacturing procedure specifications (MPS) from the pipe manufacturer as a basis for ensuring critical steel processing parameters such as the detailed rolling schedule, including, but not limited to rolling temperature, heating temperature and temperature uniformity, are controlled throughout the steel rolling process.

Mechanical property and chemical composition tests should be conducted throughout the steel making, steel rolling and pipe manufacturing process to ensure uniformity of chemical and mechanical properties of the pipe prior to being shipped from the steel and pipe rolling mills. Low yield and tensile strength test results are defined as any test results below the minimum specified yield strength ordered, and tensile strengths below those specified for the specified grade. An example of pipe standard and grades includes API 5L, PSL 2, X70 and X80; where X-70 corresponds to steel achieving a specified minimum yield strength of 70,000 psi; and so on.

II. Advisory Bulletin ADB-09-01

To: Owners and Operators of Hazardous Liquid and Natural Gas Pipeline Systems.

Subject: Potential Low and Variable Yield and Tensile Strength and Chemical Composition Properties in High Strength Line Pipe.

Advisory: The Federal pipeline safety regulations in 49 CFR Parts 192 and 195 require operators of natural gas transmission, gas distribution, and hazardous liquids pipeline systems to use pipe manufactured by a listed specification in the design of pipelines in accordance with §§ 192.7, 192.55 (a), 192.105, and §§ 195.3, 195.106, and 195.112.

PHMSA has identified an integrity issue with respect to microalloyed high grade line pipe. Tests that have been conducted on line pipe that has been installed in pipeline systems have shown that some of the pipe material has yield strengths, tensile strengths, and/or chemical compositions that do not meet the requirements of the American Petroleum Institute, Specification for Line Pipe—5L, (API 5L), for PSL 2 and the specified pipe grade. Pipe joints produced from plate or coil from the same heat may exhibit variable chemical and mechanical properties. Yield strengths below the minimum specified yield strength have been reported and yield strengths up to 15% lower than the strength values on the pipe manufacturer produced mill test report have also been reported. In some cases, the affected pipe may successfully pass strength testing methods contained in current specifications but may lead to a future pipeline integrity issue. The presence of low yield strength line pipe installed in a pipeline system may result in increased susceptibility to excessive pipe expansion or rupture during the pre in-service field hydrostatic strength test.

PHMSA wants to ensure that owners and operators of recently constructed pipeline systems are aware of the need to investigate whether their pipelines contain joints of pipe that do not meet minimum specification requirements. Pipeline owners and operators should review all MPS mill test reports and other appropriate documentation with their pipe suppliers to determine if all specification requirements have been met. Pipeline owners and operators should be aware that small deviations in steel rolling schedule parameters can have a pronounced effect on final mechanical properties. The MPS should provide adequate information concerning process details and inspection methods to ensure that the materials are uniform and will meet all specification requirements.

PHMSA advises pipeline owners and operators of in service pipelines to review their pipe specifications, pipe steel making and rolling MPS, pipe mill test reports, deformation tool results and all hydrostatic test failure results for both mill and in place hydrostatic tests 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 during recent construction projects.

Pipeline owners and operators should conduct technical document reviews on all high strength microalloyed line pipe installed during this period, review hydrostatic test failures that occurred on pipelines installed during this period and consider using methods to detect pipe expansion such as running deformation tools that detect expanded pipe in these systems if they have any knowledge, findings or pipe history that lead them to believe their newly constructed high grade line pipe systems contain line pipe joints that do not meet specification requirements. Should a pipeline owner or operator have knowledge of other high grade pipe vintages supplied at early dates that are in their operating systems that may have this problem, they should consider conducting reviews as described above with these operating pipelines to ensure that operating pressures and anomaly repair procedures are not being conducted outside of their 49 CFR Parts 192 and 195 Code parameters.

Authority: 49 U.S.C. chapter 601 and 49 CFR 1.53.

Issued in Washington, DC, on May 14, 2009.

Jeffrey D. Wiese,

Associate Administrator for Pipeline Safety.