TL;DR
A scheduled corrosion inspection confirms remaining wall thickness and corrosion rates. Measure ultrasonic thickness at the inspection grid points and compare to the minimum allowable wall.
What you might see
- corrosion rate trend indicating early wall thinning
- previous inspection report identifying active pitting areas
- process fluid changed to a higher H2S or CO2 concentration
- vessel approaching next scheduled API 510 inspection
Likely causes
Uniform corrosion from acidic process fluid (H2S, CO2, organic acids)
Pitting corrosion at the gas-liquid interface zone
Preferential corrosion at weld heat-affected zones
Erosion-corrosion at the inlet nozzle from high-velocity wet gas flow
Required tools
- Ultrasonic thickness measurement (UTM) equipment
- Gas detector (O2, H2S, LEL)
- Confined space entry kit: supplied air, rescue line, retrieval harness
- Calibrated UTM reference block
- Camera and documentation equipment
Safety first
- Confined space entry into a process separator is a permit-required confined space operation. Follow the site confined space entry procedure without exception.
- H2S may be present even after a purge. Use continuous H2S monitoring and supplied-air equipment during entry.
- All inspection findings must be submitted to the authorized inspection engineer. Do not return the vessel to service after an inspection without the engineer's fitness-for-service sign-off.
Procedure
- 1
Coordinate the inspection with a certified API 510 inspection professional. Review the last inspection report to identify the critical areas.[1]
- 2
Isolate, depressurize, drain, and certify the vessel gas-free and oxygen-safe per the confined space entry procedure.[1]
- 3
Enter the vessel following the confined space permit procedure. Conduct a visual inspection of all surfaces, nozzles, and internals.
Warning: Confined space entry into a process separator requires a permit, atmospheric testing (O2, H2S, LEL), rescue team on standby, and continuous monitoring during entry. - 4
Perform an ultrasonic thickness measurement (UTM) survey at the defined grid points. Document all readings.
- 5
Pay special attention to the inlet nozzle area, the gas-liquid interface zone, and any previously identified pitting areas.
- 6
Calculate the corrosion rate based on the difference from the previous inspection and the time between inspections.
- 7
Submit all findings to the authorized inspection engineer for the fitness-for-service assessment and the next inspection interval determination.
Sources
Sulzer Sulzer KnitMesh Process Separator / Knockout Drum general technical documentation, Sulzer
Sulzer KnitMesh process separator general internal inspection and corrosion monitoring procedures (general, API 510 framework)
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