Sonomatic has 30 years of experience with pressure vessel inspections for HTHA, including validation through metallography. We continue to invest a lot of time and energy into the development of HTHA inspection. The approach we adopt involves fine-tuning the ultrasonic set-up to the material, utilising the highest frequency the material will support. We look for changes in the acoustic scatter caused by changes in the metallurgical structure. The current Sonomatic experience level concerning HTHA includes:

  • Evaluation of 80 x 12.7 mm to 25 mm thick pipework and heat exchanger samples with selected metallography.
  • 8x UT Level 2 and 3 personnel have participated in the Lavender International HTHA course, all with high pass marks - up to 98%.
  • Technicians are trained, assessed for competency and certified internally.
  • Multiple pressure vessel and associated pipework HTHA projects are conducted every year worldwide.
  • Extensive experience has been obtained in the inspection of longitudinal seam welds in pipework.
  • A high temperature capability has been qualified for the detection of HTHA macro-cracks.
  • Techniques have been developed for the inspection of various geometries, including flanges of various sizes, nozzles and weld-o-lets.
  • Indications detected in the field have been extensively validated by metallography.

Techniques for HTHA

    A common feature of Sonomatic’s techniques for HTHA is ‘image recognition'. Our view has always been to finely-tune the ultrasonic set-up to image acoustic scatter from the material structure, and to observe changes in the images of scatter patterns.

    Off-line data analysis performed by Sonomatic includes frequency filtering and advanced contrast techniques. Frequency filtering is a useful capability that is unique to us. Our Microplus instrumentation was developed specifically for the TOFD technique and incorporates features that are not available in most other systems.

    We recommend semi-automated (encoded) TOFD and TFM scanning of both parent material and butt welds where dual-sided access is available. Additional back-scatter techniques are applied at the discretion of the analyst team.



Sonomatic Field services in combination with RAIS support were asked to turn conduct an HTHA assessment on three off Texas Towers on behalf of a client. The scope of work included weldment and base material coverage along circumferential, longitudinal and nozzle weld...


Sonomatic were approached to conduct an extensive HTHA survey on a clients Ammonia plant. The scope of work required inspection of 175 inspection “windows” covering nine pressure vessels and five piping systems. Preparation was carried out from at least 4 months ahead with tricky overseas mobilisations for both personnel and equipment...