HOW MANY EXCAVATIONS ARE REQUIRED TO CONFIRM THE ABSENCE OF SCC ON A PIPELINE?

摘要

NACE Standard Practice SP0204, Stress Corrosion Cracking Direct Assessment Methodology (SCCDA), is used by pipeline operators to infer the presence or absence of stress corrosion cracking (SCC) on a pipeline. Results from direct examinations of the pipeline are easy to interpret when SCC is found. It is more complicated when SCC is not found. How many digs are required to confirm that a pipeline has a low probability of SCC? This paper examines the relationship between SCC threat modeling and the number of digs required to conclude that a pipeline is SCC free. Results show that when a reliable inspection prioritization model is used, few digs are required to infer that a pipe has a low probability of SCC. On the other hand, when the SCC model used to select dig locations does not take into account the relevant factor leading to SCC and their interactions, the number of direct inspection required can be high. Consequently the cost of the SCCDA process is directly linked to the quality of the SCC model used to choose direct inspection locations.