Evaluating API-5L Steel of Varying Heat Treatments Through Mechanical and Ultrasonic Testing

Open Access
- Author:
- Martin, Jared
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Clifford Jesse Lissenden, III, Thesis Supervisor
Gary L. Gray, Thesis Honors Advisor - Keywords:
- Fracture Toughness
Mechanical Testing
Tensile Testing
Charpy Impact
Nondestructive Evaluation
Pipeline Steel
Material Characterization - Abstract:
- Fracture toughness is an important material property in metals such as steel alloys. Important infrastructure, like oil and gas pipelines, use such steel alloys, in their construction. Signaling a resistance to crack growth, a high fracture toughness is an important indicator of structural integrity and structural health. As such, it is crucial that essential infrastructure like pipelines are regularly monitored for changes in fracture toughness due to repetitive, cyclic use. A lower fracture toughness can be an important indicator of imminent failure. However, there is currently a severe absence of nondestructive test methods for determining fracture toughness values in situ. To this end, a nondestructive method is essential to support pipeline design and operations. The ultimate solution to this need is a “correlation curve” that relates ultrasonic nonlinear to mechanical properties like fracture toughness. The result would allow pipeline operators to evaluate fracture toughness based on a nondestructive ultrasonic pulse. In this project, we strive to replicate API-5L steel grades using a quench and temper heat treatment process at ten different tempering temperatures. Using Charpy impact testing and tensile testing, the material characteristics of the steels are quantified, including strengths and elastic moduli. Using these characteristics and the result of compliance fracture toughness testing, fracture toughness values are determined for each tempering temperature. The expansion of these results includes the completion of nonlinear ultrasonic tests on the same API-5L steels, and the correlation of said results to the subsequent nonlinear parameters for operational and maintenance use.