Inspection Technique

Inspection of steel through coatings such as composite repairs, corrosion protection tapes and subsea insulation, is not possible with standard ultrasonic inspection methods.

In many situations, other inspection techniques such as Pulsed Eddy Current and Radiography cannot achieve the necessary sensitivity or measurement accuracy. To address this requirement, Sonomatic developed Dynamic Response Spectroscopy (DRS™); an innovative ultrasonic inspection technique for mapping corrosion through challenging coatings. Low-frequency ultrasound (<1 MHz) penetrates the coating and excites the steel, causing it to vibrate at its natural frequencies.

Using advanced signal processing algorithms, these frequencies are extracted and used to determine the steel wall thickness profile. The thickness measurement accuracy is typically ±0.5 mm.

The DRS™ technique is also used to evaluate the integrity of coatings, specifically composite repairs. Flaws such as disbondment contain small air pockets which block transmission of the ultrasound into the steel. DRS™ detects these flaws where the steel response signal is lost. Flaw acceptance criteria and QA test software have been developed by Sonomatic based on Finite Element models.

HTHA is a damage mechanism caused when steel is subjected to atomic hydrogen under elevated temperatures and pressures. Under certain conditions hydrogen atoms can dissolve into methane, forming bubbles that interconnect to generate micro-fissures along the steel grain boundaries. These micro-fissures diminish the strength of the metal, leading to the development of cracks. High-temperature hydrogen attack (HTHA) cracking has the potential to result in the complete failure of essential steel components, including welds, piping, exchangers, and other critical equipment.

With over three decades of experience in non-destructive evaluation (NDE) in the field of hot hydrogen damage, Sonomatic has amassed valuable expertise. The company has engaged in extensive technique development, validated through metallography. Sonomatic also actively participates in API working groups, contributing to the authorship of sections in API 586 Recommended Practice for the inspection of high-temperature hydrogen attack (HTHA).