Published on 16-Mar-2024

Flange Inspection PAUT

Flange Inspection PAUT

Phased array gives the ability to inspect flanges without having to take them apart, resulting in quicker and cheaper inspections

Flanges are found everywhere in all industries connecting pipes, vessels and other components together. They are often exposed to corrosive fluids and challenging environments that can cause damage over time, potentially leading to failure. Accordingly, it is vital that any degradation is identified during inspections to maintain the asset and avoid leakage or catastrophic failure.

Visual inspection is a common method for inspecting flanges but this means having to shut down the plant and open the flanges which costs time and money. Phased array allows the inspection of flanges, in service, without having to take them apart, resulting in quicker and lower cost inspections.

Inspection information:

  • The inspection was performed from the bolt face as shown in the image below:

  •  A 5MHz, 32 element PAUT transducer was used for this inspection, smaller probes may also be used to get a greater amount of coverage
  • For best results the inspection should be encoded, specific scanners can also be used when applicable
  • Between 50% and 70% coverage of the flange face is achievable when inspecting from the bolt face
  • The flange being inspected has a grove for the gasket (can be seen in above image) this can be suspectable to corrosion and pitting, images below show results of inspection on this area:

When detecting defects on the flange face the extractor box position is moved so that it cover between the grove and the inside corner of the flange, the image below shows full Top view as well as the S-Scan view looking at a good area.

Defect shown in Fig. 1

Defect shown in Fig. 2


Phased array has shown to be an efficient and fast way to inspect flange faces. By using the Veo3, quick easy reporting is available at a touch of a button, with also the capability to insert specific logos and project information etc.

Full coverage of the flange face is not possible using this method as some area will be blocked by the bolt holes however sufficient is provided to confirm that the flange is sound or identify a problem which may then require further investigation.

Further research is going to be completed using FMC, this will appear on a separate application note.

For further information or support, please contact the Sonatest Applications Team:


  • Oil & Gas
  • Power Generation
  • Water Sanitisation
  • Petrochemical

Typical Parts

  • Refinery
  • Chemical plants
  • Oil & Gas platforms

Inspection Techniques

  • Manual Phased Array
  • Sectorial Scanning
  • Encoded Phased Array

Features & Benefits

  • Faster inspection speeds, lowers the cost of inspection
  • Less downtime as the flanges do not need to be taken apart to check the faces visually
  • Better resolution images can be achieved by using FMC/TFM, if required
  • The Veo3 has a 128 Gb memory allowing many scans to be recorded without having to store externally

Recommended Tool Package

  • Veo3
  • DAAH 5MHz 32E (different probes can be used depending on size of flange)
  • N57s Wedge (different wedges can be used depending on size of flange)
  • Encoder
  • Sonagel W-01


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Application Notes