Marta grabbed her hard hat and walked to the heater. The unit was humming, but she remembered an internal corrosion probe reading from three months ago—a spike in iron content. The operations crew had blamed a "blip in the feed."
She frowned. The unit processed a heavier, more acidic crude slate than last year. She grabbed the tattered, coffee-stained copy of from her shelf—the "bible" of damage mechanisms. It fell open to Section 5.1.10: Naphthenic Acid Corrosion . api rp 571 pdf
Then she saw the table she was looking for: Parameters that increase susceptibility. Her finger traced the words: Total Acid Number (TAN) > 0.5 mg KOH/g. Temperature range: 450°F to 750°F. Marta grabbed her hard hat and walked to the heater
Silence on the line.
She pulled up the crude assay for the next two years. TAN: 1.2. Temperature at the heater outlet: 620°F. The unit processed a heavier, more acidic crude
"Leo, listen," she said, flipping through RP 571 again. "Section 5.1.10, paragraph 4: 'Failure due to NAP is typically sudden and catastrophic—no thinning warning, just a rupture.' If that transfer line lets go at 700°F, we're not talking about a delay. We're talking about a fire, injuries, and a year of downtime."
Three weeks later, during the turnaround, the UT crew found the wall thickness on one elbow had dropped from 0.5 inches to 0.1 inches—in just 14 months. The "blip" had been the first whisper of naphthenic acid corrosion. Without the extra inspection, that elbow would have failed within the next operating cycle.