Phased array UT result for large pipe exposed to carbonate SCC environment in FCC (Fluid Catalytic Cracking) process

Lee, Dong Sik; SK Energy Co Ltd Ulsan Complex; Korea

Lee, D.S.; SK Energy Co Ltd; Korea

ID: ECNDT-0517-2018
Session: Applied PAUT 2
Room: G2
Date: 2018-06-14
Time: 16:20 - 16:40

The reacted product vapor flow from the top of the reactor to the main column (fractionator) in FCC (Fluid Catalytic Crack) process. There exist several corrosion contaminants, i.e. H2S, carbonate, cyanide etc. at the overhead stream of the main column. The prevalent cracking mechanism are carbonate SCC (stress corrosion crack), SSC (sulfide stress crack), and HIC/SOHIC.

During on-stream inspection crack-like flaws are detected by both radiographic test and PAUT (Phased Array Ultrasonic Test). The main column overhead piping system consist of long and large size (more than 30 inches) piping, and piping need inspection shall be expanded to total overhead piping system including overhead receiver, compressor system, and a few absorbing towers. Therefore comprehensive inspection plan shall be established. And piping stock and maintenance time shall be prepared before turnaround if the piping system shall be replaced.

All piping are categorized as 4 groups after assessment according to the POF (Probability of Failure) and COF (Consequence of Failure). Then about 150 points are selected and inspected by PAUT and some points by RT for cross check. Each crack-like indication are evaluated its reliability with API 579 Fitness for Service procedure. Eleven (11) parts are replaced during turnaround and investigated thoroughly to check the accuracy of PAUT result (type of damage, crack sizing), and to reveal what is the cause of the damage. This paper expresses the result of PAUT on-stream inspection, the result of comparison PAUT with detail investigation, and the result of root cause of the crack.