Guided Wave Ultrasonic Testing Approved for Gas Pipeline Assessments

Zeki Gokce

Director, Technical Sales, Americas

The Pipeline and Hazardous Material Safety Administration, or PHMSA, has revised the Federal Pipeline Safety Regulations in order to further improve the safety of onshore gas transmission pipelines. Given the success with Guided Wave Ultrasonic Testing (GWUT) for evaluating the integrity of gas transmission lines over the last decade, PHMSA has recently made a substantial concession to how this technology may be deployed.

A win for pipeline operators, it will be much simpler to specify the use of Teletest instruments for the inspection of pipe segments including road or railroad crossings and other difficult-to-access locations. Pipeline operators will now be able to test using guided wave without notifying the regulator as long as they apply all 18 criteria defined in a new Appendix F reference in 49 CFR § 192.921.


If an operator applies guided wave ultrasonic testing technology in a manner that does not conform with all the guidelines listed in Appendix F, it would be considered “other technology” and operators would need to seek approval from PHMSA as before.

The document becomes effective on July 1, 2020. We outline the key points here and recommend viewing this article for more information.

Wave Frequency

A minimum of three frequencies must be run for each inspection to determine the best frequency. These frequencies must be documented on the final report.

Signal and Wave Type

Both torsional and longitudinal waves must be used and documented during the inspection.

Distance Amplitude Correction (DAC) Curve and Weld Calibration

A DAC curve must be established using welds for calibration. This method takes into account the signal attenuation along with the time based on the test signal. Accessible welds must be used to set the DAC curve. A conservative estimate of the predicted amplitude for the weld is 25% CSA (cross-sectional area) and can be used when welds are not accessible.

Dead Zone

The dead zone is defined as the area adjacent to the collar where the transmitted signal interferes with the received signal. It is not possible to obtain reliable results in the dead zone. It is important to note that PHMSA requires 100% inspection of the line. The dead zone can be inspected with use of B-scan UT equipment, movement of the collar location, and visual inspection of the external surface.

Coating Types

Coating types can have an effect on the signal quality. If an inspection is done and the required sensitivity is not achieved, another type of assessment method must be utilized.

Operator Training

Only individuals who have been qualified by the manufacturer or a third-party certification scheme that is similar to ISO 9712 may conduct operator training. The training must include equipment operation, field data collection, data interpretation on cased and buried pipes.

Calibration Onsite

The GWUT equipment must be calibrated for performance in accordance with the manufacturer’s requirements and specifications including frequency of calibrations.

The structural integrity of onshore gas transmission lines depends on a robust risk management program that employs reliable test equipment to understand pipeline conditions. Eddyfi Technologies offers the Teletest Focus+™ and related GWUT technology—all fully compliant with the new rules. We are available to support our customers with implementing these changes as needed. Contact us today and stay Beyond Current.

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