(227b) Corrosion Prevention, Protection & Control in Cdu Overhead System

Saudi Armco's Yanbu Refinery, is commissioned in 1983. The hydro skimming refinery has a crude unit of capacity 235 MBPD.

YR CDU Overhead system condenses the column overhead vapor .It is protected with chemical injections, filming and neutralizing Amine, through the reflux line. Overhead line operates under dry condition without any condensation in the line. In 1997 30? vapor line vertical portion has two pinholes with pipe thickness reducing from 9.5 mm to 5.8 mm.

YR modified the system using technology and operational improvement with a new overhead line provided with wash water and chemical injections .The line is converted into two sections as dry and wet sections. The system operated for the four years and inspected in 2001 revealed metal loss in two locations, the first one in the dry section and the second at upstream and downstream the condenser that was in-services since 1983.

Low thickness in the dry section is due to

? Acid corrosion

? Under deposit corrosion when the pH is in between 6.8-7.2

? The high overhead vapor velocity.

Dry section is modified by

? Cladding at the part upstream of the water injection point to eliminate the under deposit corrosion.

? Moving the water injection to convert the system to wet system

? Upgrading the overhead Line to 36?.

Operating conditions improvement

1. Bettering crude tank supply system with steady crude quality,

2. Desalter operation.

? Condensate as wash water at 3% and 8% of crude flow.

? Desalter upgraded to improve performance.

3. Overhead system;

1. A new line to have the wash water directly from crude unit overhead receiver maximizing steam condensate recycling.

2. Better monitoring with pH analyzers and additional corrosion probes .