Offshore Underwater Fixed Structure Integrity Assessment Using LRUT, PEC & ACFM Advanced Technologies with Minimal Marine Growth Removal

Abstract

Abstract Offshore underwater structures degrade over time due to the harsh environment and operating conditions of the structure leading to potential problems such as fatigue cracking or corrosion. This necessitates the need for regular inspection, monitoring, and possibly repair to ensure that the structurescontinue to operate safely. However, conventional inspection techniques face significant challenges when inspecting subsea structures, particularly related to the access of the area of interest. Removal of marine growth in these areas and the safe use of remotely operated vehicles (ROVs) can be time consuming and problematic. To address these challenges, a unique approach was developed that combines different advanced non-destructive testing (NDT) techniques to maximize productivity and minimize intrusions while ensuring the data collected is the high quality needed for integrity assessment, allowing for the safe operation of critical assets. This approach involves a combination of long-range ultrasonic testing (LRUT) technology with marinized transducer tooling, underwater Pulsed Eddy Current (PEC) testing, and underwater Alternating Current Field Measurement (ACFM) to inspect subsea structures. The LRUT technology is initially used to screen piles for overall condition with marine growth only needing to be removed at the tool location. PEC is used to verify critical findings without removing any marine growth. ACFM is used to inspect underwater welds for fatigue cracks, all with minimal removal of marine growth. This approach has successfully implemented in the field, including the use of underwater marinized LRUT collars, to inspect approximately 1000+ piles of circular piles (LRUT for 700+ circular piles and ACFM & PEC for 1000+ piles which includes circular and hexagonal piles) with different diameters and wall thicknesses. This technical paper provides details about the challenges encountered during implementation and how they were overcome. Furthermore, it shares real site experience and results of this innovative inspection program. The results were validated by cross-checking with other techniques such as underwater ultrasonic thickness gauging (UTG) and close visual inspection (CVI) by qualified divers to ensure accuracy and reliability of the results.