The choice of re-qualification testing method for portable cylinders is based on a variety of factors. In most cases, DOT regulations offer choices.
This 5 part article discusses the different choices when it comes to re-qualification testing methods for portable cylinders. Each part will identify the type of re-qualification testing method and provide a brief description of each. These choices include such methodologies as:
- Visual Examination Method
- Hydrostatic Testing Methods
- Water jacket method
- Direct expansion method
- Proof pressure method
- Acoustic Emission Method
- Ultrasonic Examination Methods
- Automated ultrasonic examination
- Hand-held ultrasonic examination
- Other Test Methods
Part 1 addressed the Visual Examination Method, Part 2 addressed Hydrostatic Testing Methods, Part 3 addressed Acoustic Emission Method, Part 4 addresses Ultrasonic Examination Methods and Part 5 will address Other Test Methods.
Ultrasonic Examination Methods
Automated ultrasonic examination – An automated ultrasonic examination system examines the entire cylindrical surface of a cylinder with multiple transducers that simultaneously measure thickness with a straight beam and detect discontinuities using several angle beams inspecting the cylinder wall from different directions. Automated ultrasonic examination is a mandatory re-qualification method for DOT UN cylinders specifically with a tensile strength greater than or equal to 950 MPa. Increasingly, ultrasonic examination is being used as the preferred re-qualification method, particularly for cylinders transporting high purity, flammable or toxic gases. Ultrasonic examination is a direct measurement and assessment of cylinder integrity, which is not the case for hydrostatic methods. Ultrasonic examination permits are written for both 5-year and 10-year re-qualification cycles.
Hand-held ultrasonic examination – Hand-held ultrasonic examination is not a re-qualification method by itself. It must be accompanied by either Acoustic Emission or automated ultrasonic examination. Hand-held ultrasonic examination is paired with Acoustic Emission to characterize and size flaws that emitted acoustic emissions during pressurization and, ultimately, determine whether or not the cylinder is suitable for continued service. Hand-held ultrasonic examination can use both straight beam and angle beam testing techniques to measure wall thickness or detect discontinuities.
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