The potential for dramatic and costly pipeline failures continues to be a top concern for regulatory agencies, pipeline operators and energy providers due to the risk to human life and the environment (something like that). In 2017, the Pipeline and Hazardous Materials Safety Administration (PHMSA) issued a Final Rule that mandates several preventative and documentation processes designed to standardize the measurement, testing and assessment of pipeline inspection procedures. Non-Destructive Testing (NDT) methods are invaluable when performing field tests on existing oil and natural gas pipeline, but in some cases, Destructive Testing (DT) methods are needed to reveal more in-depth structural analysis.
The primary methodology of Destructive Testing involves carrying out physical test methods to the point of a specimen’s failure. The results of these methods can illustrate how a material’s characteristics and microstructure react to controlled stressors of tension, time, torque, and temperature.
These DT methods include:
- Tensile strength test: Tensile testing involves clamping a sample into a fixture, then imparting controlled and sustained tension until failure occurs. The results of this test provides data to assist in the selection of appropriate materials for the application.
- Fracture Toughness: One of the most critical properties of pipe material, this test involves creating test specimens from the pipe wall that include a simulated crack. The specimen is then subjected to cyclic stresses that cause the crack to grow. The toughness of the material is determined by measuring the number of cycles at different stresses the material can withstand.
- Bend testing: Bend testing tests the flexibility of a material. Test material samples are placed in a holding fixture, and caused to bend, but not fracture. The ductility of a metal is an important component in tensile, compression and fatigue characteristics.
- Charpy impact test: This method determines the toughness or impact strength of the material in the presence of a flaw or notch. A controlled weight pendulum is swung from a set height into a standard notched specimen. The force of the impact absorbed by the sample provides material characteristics important to the final product.
To maintain compliance to the Final Rule, terminal and pipeline owners are obligated to operate their pipelines safely, requiring an effective inspection, maintenance and repair program. To be in compliance, operators are accountable for the development, documentation, implementation, execution and assessment of pipeline inspection methods. Meeting these requirements means a safer energy grid for both owners and the public, and saves operators from potential disasters to their corporation’s goodwill, finances and personnel.