Thread Content
Protection Techniques against Stress Corrosion Cracking in Equipment of the Catalytic Cracking Regeneration System I. Overview Numerous cracks have been found in the equipment of catalytic cracking units, particularly those for heavy oil catalytic cracking, as well as in the main components of the flue gas system (including regenerators, three-spin separators, etc.). Most of these cracks occur at weld areas, while those that appear in the base material are often located near the weld points made using insulation pins; many of them are penetrating cracks. This issue has become a major hazard for the heavy equipment in refineries, posing a serious threat to their safe operation. The electrochemical theory of stress corrosion suggests that cathodic protection can prevent sensitive systems from suffering from stress corrosion, or stop the growth of cracks that have already formed. Using an anode metal with sufficient activity for coupling, so that the potential after coupling is lower than the stress corrosion potential, is a simple and feasible method. II. Technical Features: Based on the principle of crack formation in catalytic regeneration system equipment, active metals are used for electrochemical protection, which not only prevents the initiation of stress corrosion cracks but also inhibits their further propagation. This technology allows the device to operate at low temperatures, which contributes to its safe operation, reduces heat loss, and facilitates equipment maintenance as well as operational safety. The selected active corrosion-resistant material combines crack protection with resistance to uniform corrosion, thereby enhancing the reliability of protection; its effective corrosion resistance lasts for over 10 years. Active metals were installed using the thermal spraying method, successfully solving the problem of limited space for corrosive media. Active metals provide both dielectric isolation and electrochemical protection. III. Industrial Applications: At Cangzhou Refinery, after the use of heavy oil in the secondary catalytic converter over the past few years, 156 cracks of varying degrees were found in more than a dozen circumferential welds of the secondary catalytic converter during maintenance work. These cracks occurred in the welds, fusion zones, and heat-affected zones; many of them were through-cracks, with the longest crack measuring 500 mm. Due to the significant safety hazards associated with the regenerator, which have severely impacted the safety and normal operation of the facility, metal coating protection technology has been adopted. After one year of operation, inspections of the metal coating applied to the dilute-phase and dense-phase sections of the two catalytic regenerators showed that the metal coating had good adhesion to the heat-insulating and wear-resistant lining; there were no signs of cracking in the wear-resistant lining, and its surface remained in excellent condition. In contrast, the surface of the 20R sample showed some yellow rust. Flaw detection was carried out on the relevant welds; the ultrasonic testing was performed on the B13 and B11 circumferential welds (the upper and lower circumferential welds in the transition zone), and the results showed no cracks detected in any of the inspected areas.