Guided Wave / LRUT is primarily a screening technique used to identify areas that may require additional examination. A reported indication should not automatically be considered fully characterized or sized based on the screening response alone. Follow-up examination should be selected based on the specific condition or engineering question that must be resolved, such as physical location, remaining wall thickness, feature extent, morphology, interaction, or suitability for assessment.

The main question after a Guided Wave indication is not "which follow-up technology is best," but "what information must the next examination provide?"

Start with the inspection objective

Before selecting the follow-up method, define what must be confirmed. Review the Guided Wave location, direction, reported CSC or classification, signal quality, test range, and nearby geometric features. Then determine whether the follow-up examination needs to:

  • determine whether a corresponding damage condition is present;
  • determine remaining wall thickness;
  • define axial and circumferential extent;
  • characterize localized versus distributed corrosion;
  • separate geometry from actual damage;
  • provide dimensions suitable for engineering assessment;
  • or determine whether additional access or excavation is required.

The follow-up technique should be chosen to answer that specific question.

Screening versus characterization

Guided Wave provides long-range screening coverage, but screening results do not by themselves provide the same localized dimensional information as a direct wall-thickness or corrosion-mapping examination. Some follow-up technologies may also function primarily as screening tools depending on how they are configured and qualified. Using one screening method after another can provide useful supporting information, but it should not automatically be described as full prove-up or sizing. Where engineering assessment requires actual wall-loss dimensions, the selected examination should be capable of producing measurements suitable for that assessment.

Localized UT and corrosion mapping

Conventional UT, encoded UT, C-Scan, PAUT, or another qualified localized ultrasonic method may be appropriate when the goal is to measure actual wall thickness or define the profile and extent of a condition. The examination should cover the reported Guided Wave location and enough surrounding area to account for datum tolerance, signal spread, nearby features, and the possibility that the reported reflector does not represent the full extent or only condition within the examination area. Document the inspected area, calibration, surface condition, minimum readings, scan resolution, excluded regions, and any limitations that could affect confidence in the result.

SRUT

Short-range UT may be useful in specific areas where localized ultrasonic coverage is required around supports, attachments, welds, or other restricted geometries. Its role should be defined by the written procedure and the specific inspection objective. Depending on the application, SRUT may provide localized screening or limited examination coverage depending on the technique, configuration, and qualified procedure, but it should not automatically be treated as equivalent to a full corrosion map or direct dimensional prove-up. Document the actual coverage, limitations, calibration, scan direction, inaccessible regions, and what conclusions the data can support.

EMAT

EMAT can be valuable in selected applications where material, surface condition, temperature, geometry, and equipment configuration make the technique appropriate. Its role can vary significantly depending on the examination setup. It may be used for screening, detection, or more localized examination depending on the qualified procedure. The report should clearly state what the EMAT examination establishes, what area was covered, what sizing capability was used, and whether additional direct measurement is required.

QSR

QSR may also be used in selected applications where the equipment, qualified procedure, personnel, geometry, and inspection objective support its use. Its role should be described precisely. If the application is screening, call it screening. If the qualified procedure supports localization, characterization, or sizing, state that specifically. Do not assume that the term QSR by itself establishes equivalent capability to direct wall-thickness measurement or corrosion mapping.

Match the method to the decision

The correct follow-up method depends on the information needed. If the goal is only to determine whether an area warrants further examination, a screening technique may be appropriate. If the goal is to determine actual remaining wall thickness, corrosion dimensions, morphology, or dimensions for engineering assessment, use a technique qualified to provide those measurements. The Guided Wave / LRUT reporting workflow should preserve the original shot, reported location, follow-up examination, photos, inspection coverage, limitations, and final result so the full inspection history remains traceable.

Questions inspectors ask

Is another screening method automatically considered direct confirmation of a Guided Wave indication?

No. A second screening method may provide useful supporting information, but it should not be treated as equivalent to localized characterization or dimensional confirmation unless the applicable procedure and method capability support that use.

What should be used when actual wall-loss dimensions are needed?

Use a qualified localized examination capable of producing the measurements required for the inspection or engineering decision, such as direct UT, encoded corrosion mapping, PAUT, or another suitable technique.

Can SRUT, EMAT, or QSR still be useful after Guided Wave?

Yes. Their usefulness depends on the pipe configuration, access, expected damage, procedure, coverage, and the specific question that must be answered.

Does follow-up eliminate engineering review?

No. The follow-up examination improves the physical evidence available for review. Qualified inspection and engineering personnel still determine whether monitoring, additional examination, assessment, repair, or other action is required.