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Phased Array Ultrasound as a Replacement for Radiography


An example of carbon steel pipe corrosion that can be mapped using a scanner

Summary

In nondestructive evaluation (NDE), or nondestructive testing (NDT), many codes allow inspectors to substitute one inspection method with another, as long as certain requirements are met. Additionally, non-code-based inspection methods are constantly being reviewed to improve processes and reduce costs. Ultrasonic methods have become a popular and accepted substitute in inspections that previously employed radiographic methods.

Introduction

Radiography and ultrasound are complimentary NDT techniques. Both can volumetrically inspect welds and components for defects like cracks, lack of fusion, porosity, etc. The choice of one over the other often depends on external process decisions or small differences in the detection capability for a particular test. However, ultrasound has gained momentum as a replacement for radiography both in practice and in the codes of major organizations such as ASME (American Society of Mechanical Engineers) and API (American Petroleum Institute). Although most codes do not specify the ultrasonic method, phased array (PA) ultrasound, in particular, has become the most popular replacement method in inspection processes. PA is often also combined with time-of-flight diffraction (TOFD) when inspectors use acquisition units and scanners that can accommodate both methods simultaneously. In the past, code-based inspection processes typically followed code cases or appendixes. However, after increasing use and acceptance in industry, ultrasonic inspection processes are being added directly to the main body of major codes, for example, ASME Sec. V. Art. 4 from 2010 onwards. Phased array ultrasonic equipment is becoming more portable, affordable, and easier to use, making ultrasound a practical, safe replacement for radiography.

Typical Advantages of Ultrasound (over Radiography):

  • High probability of detection (POD), especially for cracks and lack of fusion:
    • Ultrasound tends to detect planar flaws better than radiography in most studies.
  • Accurate sizing of defect height and fewer rejects or repair using Engineering Critical Assessment:
    • Ultrasound permits defect height measurement, which enables volumetric consideration of flaw severity (instead of only flaw type and length).
  • Does not emit radiation, does not cause hazards, and does not require additional licensing or personnel.
  • Does not require screened-off areas. Work in proximity to ultrasonic testing can continue uninterrupted.
  • Does not generate any chemical or waste material (as opposed to film-based radiography, which does).
  • Real-time ultrasonic analysis of welds can provide instant evaluation and feedback to a welder.
  • Setup and inspection reports are in electronic format (as opposed to film format in radiography).

Examples of Codes with Ultrasound Replacing Radiography

  • ASME Code Case 2235
  • ASME Code Case 179
  • ASME Code Case 168
  • ASME Code Case N-659
  • ASME Code N-713
  • API 620/650 App. U
  • ASME Sec. V Mandatory Appendixes

Typical Ultrasonic Equipment and Inspection Requirements

  • An acquisition unit with full, raw A-scan data retention and position-encoding ability (for example, an OmniScan® flaw detector or FOCUS PX instrument).
  • A scan plan and procedure that documents the inspection strategy and essential parameters (for example, parameters that are set up using the NDT SetupBuilder software).
  • An industrial scanner (with position encoder) that can repeatedly scan a weld or component (semiautomatically or automatically):
    • The choice of scanner model is based on the number of welds, pipe diameter, and other application variables.
  • Deliverable data:
  • Demonstrated performance of equipment, procedure, operator, and inspection process.
  • Alternative acceptance criteria, as required.
  • Probes, wedges, couplant delivery equipment, and other accessories.
  • Proper training and certification of personnel.

An example of carbon steel pipe corrosion that can be mapped using a scanner
The OmniScan MX2 (multi-group capable) [left] and OmniScan SX (single group) flaw detectors.

Using the RollerFORM scanner to inspect flat bottom holes
Amplitude C-scan using the OmniScan flaw detector


Fully automatic WeldROVER scanner (left) and semiautomatic HSMT-Compact scanner with an OmniScan MX flaw detector.

Conclusion

The replacement of radiography with ultrasound has become an industry trend, as well as a code-accepted practice. Easy-to-use and affordable portable phased array equipment and associated software are accelerating the use of ultrasound. The main reasons for this continuing trend include savings in process cost and time, improved safety of operators and others in surrounding areas, and the use of alternative acceptance criteria. The increased use of ultrasound has led to a decrease in part rejection and repairs.

Olympus IMS

Products used for this application


Industrial Scanners

The capacity to accurately position probes according to the surface being inspected greatly influences inspection quality. Olympus offers a wide range of industrial scanners and accessories to assist inspectors in their work. Scanners come in various configurations including one or two encoded axes with manual or motorized motion.

NDT SetupBuilderNEW

NDT SetupBuilder is a new PC-based software allowing to create inspection setup and visualize beam simulations. This software presents multiple features for easy, fast, and comprehensive inspection strategy elaboration that can directly be imported in the OmniScan MX2.

OmniPC Software

This new software is the most efficient and affordable option for OmniScan data analysis, and features the same analysis tools provided in the OmniScan onboard software, with the added flexibility of running on a personal computer.

OmniScan MX2

The OmniScan MX2 now features a new phased array module (PA2) with a UT channel, and a new two-channel conventional ultrasound module (UT2) that can be used for TOFD (Time-of-Flight Diffraction), as well as new software programs that expand the capabilities of the successful OmniScan MX2 platform.

OmniScan SX

The single group, lightweight OmniScan SX features an easy-to-read 8.4 inch (21.3 cm) touch screen and provides cost-effective solutions. The OmniScan SX comes in two models: the SX PA and SX UT. The SX PA is a 16:64PR unit, which, like the UT-only SX UT, is equipped with a conventional UT channel for P/E, P-C or TOFD inspections.

Phased Array Probes

Phased array application-specific probes have a range from 0.5 MHz to 18 MHz and may come with 16, 32, 64, or 128 elements. Special probes may have up to hundreds of elements.

TomoView Software

TomoView is a powerful and flexible PC-based software used for design, data acquisition, visualization, and analysis of ultrasonic signals.
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