Destructive Examination of Ultra-Selective Exchangers (USX’s)

Chevron Phillips Chemical Company, LP (CPC) operates Stone & Webster cracking furnaces at its various ethylene plants in the Gulf Coast area. Stone & Webster furnace technology utilizes BORSIG USX-Omega primary quench heat exchangers. The USX exchangers are designed to quench the heater effluent by producing steam. Boiler feedwater (BFW) gravity flows from the steam drum through the outer tube of the vertical USX exchangers. Each USX has a primary and secondary pass. During a process upset, the USX exchangers were exposed to temperatures that exceeded their design conditions.

A Fitness-for-Service (FFS) assessment was commissioned on the USX-Omega exchangers after the equipment operated above the design temperatures limits for approximately 5 hours. The FFS assessment followed API 579-1/ASME FFS-1, Part 10 methodology (Assessment of Components Operating in the Creep Range), starting with a Level 3 engineering analysis (Phase 1) and metallurgical analysis and destructive testing (Phase 2).

This paper discusses API 579-1/ASME FFS-1 Part 10, Assessment of Components Operating in the Creep Range, destructive metallurgical testing that was pursued to establish suitable remaining life so that the equipment could be returned back to service with assurance of safe, reliable operations.