Detection and sizing of defects in large foundation bolts using HOMC guided wave annular array ultrasonic sensor

Foundation bolts are used extensively in various areas such as construction, engineering, automobile and mechanical industries for connecting steel structures to concrete structures. These bolts are prone to failure in extreme field conditions, that is, vibrations, elevated temperature, moisty and corrosive environment. Major reason for failure of foundation bolt is opening of fatigue cracks on fillet portion in a T-head foundation bolt due to several reasons like overloading, corrosion and poor installation. Abrupt failure of these bolts may lead to breakdowns, that is, production loss and unsafe condition. Real-time condition assessment of bolts is essential for early detection of defects, that is, predictive maintenance. A state-of-the-art sensor is designed for continuous monitoring of cracks and their growth in foundation bolts using HOMC guided wave ultrasonic testing was developed. The methodology overcomes harsh ambience, that is, high temperature, moist environment and continuous water spillage over the bolt with limited accessibility of tail end (thread side). A higher sensitivity of cracks as small as 2% of the diameter was achieved in M80 and M100 foundation bolts of approximately 2850 to 3350 mm in length. A robust and reliable sensor assembly was designed, and brownfield installation was achieved in harsh conditions of a hot rolling mill.