Ultrasonic and Automated Ultrasonic Testing (UT / AUT)

Ultrasonic Testing (UT) is a specialist inspection discipline that can be used for detection of surface and internal flaws in a range of materials (typically carbon steel and alloys, but also concrete, composites and even wood). It is also very common for UT to be used to gauge the thickness of materials with parallel surfaces (such as pipe wall thickness).

Ultrasonic Testing is a key part of corrosion assessment surveys and our asset integrity management system, quality control of site welding (see our news and projects pages) and Marine Classification Surveys.

ConocoPhillips Judy Platform – Axiom staff have just completed an Ultrasonic Testing (PCN II 3.1, 3.2) project supporting the annual fabric maintenance campaign on this platform.

Judy OIE, Forbes Scott-Lodge provided this feedback:

“Just a quick note to say how happy I have been with the attitude and professionalism of your technicians. They have carried out their duties diligently and have actively participated in the platform Safety initiatives.”

How it works..

Manual (Pulse Echo) UT works by sending a short ultrasonic pulse wave, from a single transducer (probe crystal) into the item to be tested. This energy is reflected back into the transducer (as a pulse echo) by either the back wall of the item or by a discontinuity within it. Amplitude and arrival time of pulse echo can be used to gauge thickness or presence of flaws.

Automated UT (Time of Flight Diffraction – TOFD –  and Phased Array-PAUT) refers to  extremely advanced methods of inspection that can provide an alternative to traditional radiographic inspection (of butt welds for example).

TOFD works by using a pair of probes (typically mounted on a buggy) – receiver and transmitter – emitting two ultrasonic waves. In undamaged materials both waves are detected by the reciever, one travelling along the surface and the other along the back wall.  A defect in the material causes diffraction of the wave from the crack tips, allowing size and location of defect to be established by trigonometry and known time of flight (of surface wave).

Phased Array UT utilises a single probe composed of multiple small ultrasonic transducers (as opposed to the single transducer used by manual UT) that can be pulsed independently to, in effect, generate directional beams from a single location. This provides a visual image, showing a slice through the material under test. Phased array is very efficient both in terms of defect detection and speed of test.

Company Background and Competency

Axiom personnel were at the forefront during the early development of ultrasonic and eddy current testing (see below)and this innovative approach continues today with the adaptation of existing technology to meet new challenges (testing through TSA coating using Eddy Current or Ultrasonic Testing of stainless steel mast bolts in the renewables industry, for example).


Former Technical Director, Benny Donnelly, here shown demonstrating Ultrasonic Plate Testing to HM the Queen in the mid-sixties, was heavily involved in the early development of this discipline (via Babcock and Wilcox).



A key member of the team that introduced the first ultrasound machines to hospitals, equipment developed by Benny is on display at museums in Glasgow.

Axiom has many years experience with Ultrasonic Testing disciplines and the current inspection team continue to look for new applications of the technology

Our senior technicians are qualified to PCN II in both Pulse Echo (3.9) and AUT and can draw upon a vast range of experience of testing welded fabricated assemblies, pile welds, oil & gas related forged and clad parts, pressure vessel welds, crane structure welds, bridge structure welds, boilers, forgings & castings.

We are able to write procedures for most site applications of UT and are able to provide a high degree of support to our clients regarding remedial action advice, suitable test specifications and risk based inspection criteria


Marine Classification Society (LLOYDS EMEA) Vessel Surveys

Axiom provide a specialist vessel survey service for local ship repair and marine engineering company Garvel Clyde Ltd.

To date in 2013 we have completed Ultrasonic (UT) hull thickness measurement surveys on Caledonian MacBrayne vessels ‘Isle of Arran’, ‘Clansman’, ‘Loch Portain’ and ‘Caledonian Isles’.

We pride ourselves on offering an integrated service to the marine industry and operate worldwide from our offices in Glasgow and Aberdeen.

Our marine offering includes:

Hull Inspection and Ship Surveys (marine classification hull thickness measurements)

  • A full range of Non-Destructive Testing (NDT) and inspection services applicable to the marine environment (Eddy Current, Ultrasonic and Magnetic Particle Inspection – e.g. structural inspection of cranes / davitts)
  • Tank / Vessel inspection
  • Crane and Lifting Equipment (fixed and loose) Examination (under LOLER / ICHCA regulations)
  • Rigging and Lifting Services (from personnel supply to full service package)

Commitment to Training and staff Development

Axiom recognise that there is a looming skills shortage in the UK offshore industry and by providing a structured career development path for our staff, alongside an apprenticeship scheme for new entrants, we aim to meet the challenges ahead.

Qualifications gained by our staff so far in 2013 range from Magnetic Particle Inspection (trainee) through PCN II Plate Testing (Apprentice) to Time of Flight Diffraction / AUT (Senior Engineer).

In between offshore projects, our  Team Leaders are often kept busy running onshore inspection projects – we believe that the range of techniques (and defects found) within the onshore infrastructure and fabrication industries makes them ideal proving grounds for NDT technicians with offshore aspirations and all of our core team have cut their teeth in this way, on our own projects.


Axiom  use portable UT sets for manual UT that can be easily operated by rope access technicians or in  confined spaces, allowing its use in complicated and hard to access areas (module pipework, wellhead bays, wind turbines, internal bridge sections etc..).

Automated (computerised) UT equipment is bulky and although it can be used from ropes, consideration needs to be given to the operators comfort and ability to access all areas.

UT sets are not intrinsically safe (i.e. control measures and a ‘hot work spark potential permit’ may be required in explosive atmospheres), but the technique itself is non-hazardous to the operator, passers-by or machinery.

Visit our Resource Area to find out about or buy British Standards applicable to Ultrasonic Testing



Advantages are:

  • UT is a sensitive technique and has real time accuracy in determining wall thickness and its capability for estimating size, orientation and shape of defects deep within a weld/material. For example UT wall thickness assessment is a staple part of corrosion assessment programmes for offshore high pressure cement & mud pipework.


  • A potential drawback is the high cost of equipment and training, as well as the need for a greater degree of competency in the operator.

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