[4C1] Reducing false calls in HTHA inspection through phase coherence imaging (PCI)
S Baba, V Chumillas and F Turcu
Evident Europe GmbH – UK Branch
Presented by G Luckett, Evident Europe GmbH – UK Branch
High-temperature hydrogen attack (HTHA) is a critical damage mechanism that can occur in ageing in-service pressure vessels and heat exchangers in the oil & gas industry. In its initial stages, HTHA typically develops as micron-sized fissures in a component’s material under certain conditions: the presence of hydrogen molecules from the petrochemical product; the elevated temperature of production; and the type of alloy or age of the component. Industry-recommended practices such as API RP 941 mention the use of a combination of NDT technologies, including time-of-flight diffraction (TOFD), phased array (PA), total focusing method (TFM), velocity ratio, etc, to detect potential HTHA damage and assess its stage. While early-stage detection of HTHA is essential for the safe operation of petrochemical assets, the industry has been searching for effective and reliable ways to distinguish such indications from manufacturing flaws such as inclusions or porosities.
Phase coherence imaging (PCI) is an ultrasound technique derived from the total focusing method. It has been developed and deployed on portable flaw detectors to help detect discontinuities that generate diffracted signals rather than reflections in ultrasonic testing using TFM. Its potential in detecting small-sized porosities and inclusions may generate, together with the other techniques, a more comprehensive picture of the component under test and help differentiate between clusters of HTHA indications and randomly distributed material-characteristic indications.
This paper presents the PCI technique and assesses its potential to detect both HTHA and porosities. Data acquired on real samples using TOFD, PA, TFM and PCI shows how PCI can contribute to an improved assessment of the sample under study and help reduce false calls in HTHA inspection.
High-temperature hydrogen attack (HTHA) is a critical damage mechanism that can occur in ageing in-service pressure vessels and heat exchangers in the oil & gas industry. In its initial stages, HTHA typically develops as micron-sized fissures in a component’s material under certain conditions: the presence of hydrogen molecules from the petrochemical product; the elevated temperature of production; and the type of alloy or age of the component. Industry-recommended practices such as API RP 941 mention the use of a combination of NDT technologies, including time-of-flight diffraction (TOFD), phased array (PA), total focusing method (TFM), velocity ratio, etc, to detect potential HTHA damage and assess its stage. While early-stage detection of HTHA is essential for the safe operation of petrochemical assets, the industry has been searching for effective and reliable ways to distinguish such indications from manufacturing flaws such as inclusions or porosities.
Phase coherence imaging (PCI) is an ultrasound technique derived from the total focusing method. It has been developed and deployed on portable flaw detectors to help detect discontinuities that generate diffracted signals rather than reflections in ultrasonic testing using TFM. Its potential in detecting small-sized porosities and inclusions may generate, together with the other techniques, a more comprehensive picture of the component under test and help differentiate between clusters of HTHA indications and randomly distributed material-characteristic indications.
This paper presents the PCI technique and assesses its potential to detect both HTHA and porosities. Data acquired on real samples using TOFD, PA, TFM and PCI shows how PCI can contribute to an improved assessment of the sample under study and help reduce false calls in HTHA inspection.
