Oxidation | Materials And Corrosion Control
| Damage Mechanism | Oxidation |
| Damage Description | Oxygen reacts with carbon steel and other alloys at high temperature converting the metal to oxide scale. It is most often present as oxygen in the surrounding air (approximately 20%) used for combustion in fired heaters and boilers. |
| Affected Materials | · Iron based materials including carbon steel and low alloy steels.
· All 300 Series SS, 400 Series SS and nickel base alloys also oxidize to varying degrees, depending on composition and temperature. |
| Control Methodology | · Resistance to oxidation is best achieved by upgrading to a more resistant alloy.
· Chromium is the primary alloying element that affects resistance to oxidation. |
| Monitoring Techniques | · Process conditions should be monitored for establishing trends of high temperature equipment where oxidation can occur.
· Oxidation of carbon steel begins to become significant above about 1000°F (538°C). · The 300 Series SS are resistant to scaling up to about 1500°F (816°C). · Temperatures can be monitored through the use of tube skin thermocouples and/or infrared thermography. · Loss in thickness due to oxidation is usually measured using external ultrasonic thickness measurements. |
| Inspection Frequency | · NDE and visual inspection at T&I |
| KPIs | · Strictly avoid scaling as this generally indicates that a metal has been exposed to a temperature exceeding its high temperature mechanical capability (i.e., it is in the creep range).
· Establish a maximum temperature for the metal beyond which it should not be operating. Maximum temperatures are given by API RP 571. Maximum temperatures established based on creep life may be lower than for oxidation. These maximum temperatures limited by creep are given by API 530. · Monitor O2 levels in the cold VGO feed and use anti oxidant as needed. |
| Reference Resources (Standards/GIs/BPs) | · API RP 571 (DM #11)
· API STD 579 Part 11 |