Hand Held Ultrasonic Sizing of Stress Corrosion Cracking

Stress corrosion cracking (SCC) is now globally recognized by pipeline operators as a significant threat to the safe and efficient operation of their systems. Onshore natural gas, oil and refined products line pipe steels have all been susceptible to this form of environmentally assisted cracking, which can develop as either low or high pH SCC. Over the years, the pipeline industry has developed several non destructive examination (NDE) techniques to identify, document and evaluate the severity of a SCC indication, including magnetic particle inspection (MPI) and ultrasonic (UT) sizing. While MPI can locate and assess the surface dimensions of the cracks within the SCC indication, measurements of crack depth within the colony have not been as easily obtained under field conditions. Researchers have been developing field based hand held ultrasonic (UT) sizing techniques to determine the actual crack depths. The UT determined SCC crack depths are incorporated into engineering assessments and crack growth models (used in risk algorithms), potentially enabling operators to effectively address, monitor and thus manage this time dependent threat. This paper will discuss our experiences since the mid 1980’s with UT crack sizing, the techniques that are available in the industry, the limitations that still exist, and the benefits of using a new UT assessment transducer to assess SCC crack depths.