20" Dia CS elbow with multiple cracks on the extrados (Rich Benfield Solution)

[Alpha Charlie]

We have a CS 20"-12.7mm THk elbow installed on rich benfield solution. Operating Temp: 123.5 C while pressure: 29.5 Kg/cm2. Line is stress relieved as per process design conditions. Benfield CS lines are monitored against thickness loss. Particular elbow was found with multiple surface cracks on the extrados and few cracks on the intrados. All cracks are in the direction of flow and longest is 4" long but estimated approx. depth is not more than 2-3mm based on hot penetrant test bleed out. CS elbow was insulated with mineral wool.

Any idea what might be the reason of these surface cracks since we never experienced such an anomaly before. Elbow material was confirmed to be CS by PMI of removed shavings.

 

It is technically correct to say there have been no new refineries built in decades, but it's not like there has been no investment.
All of them have had serious revamps, as well as upgrades to climb what I call the 'alloy ladder' in the face of opportunity crude*.

* The 'opportunity' in opportunity crude refers to jobs for corrosion engineers.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."