Evaluation and Simulation of HTHA Damaged Specimen using UT Advanced Techniques

High Temperature Hydrogen Attack (HTHA) is a wellknown phenomenon that impacts the design, operation, and maintenance for syngas production facilities (e.g., hydrogen and carbon monoxide plants). Recommendations regarding material selection and inspection are given by API 941 and API RP 586 [1], that is currently under revision after Tesoro accident. The new rules have highlighted the need to adapt inspection with more advanced NDT methodology, improving the detection of early stage HTHA damage, then supporting a Fitness for Service approach. This paper makes an overview of various projects funded by Materials Technology Institute (MTI) regarding the assessment and improvement of the performance of such UT advanced NDT for HTHA detection, by means of CIVA UT simulations after a detailed metallographic review and statistical modeling of material inclusions and HTHA damage distributions of field samples. HTHA damage inputs and comparisons between experimental and simulated UT images are consistent for different damaged samples (different levels and types of damage, especially for welded samples), different UT acquisition settings and different inspection frequencies. The unprecedented use of HTHA damage distribution laws and NDT simulations of nonmetallic defects and HTHA damage are promising tools which may then used to assess the limits of existing NDT and to define optimized probes and procedures relying on advanced ultrasonic examinations.