Long Term Operating Experience With Corrosion Control In Industrial Axial Flor Compressors

One of the primary causes of flow path failures in industrial axial flow compressors has been attributed to or is related to corrosion damage. Over the years, a number of corrosion mitigations have been utilized by various manufacturers and users. This paper summarizes several long term monitoring and assessment programs that evaluated the effectiveness of the mitigation steps and makes recommendations for future operation. The monitoring programs included detailed metallurgical analyses of corroded stator and rotor blades, material captured in inlet filter pads, flow path deposits and corrosion coupons. The hardware was examined at various run time intervals that ranged between 2 to 12 years. When possible, corrosion damage was mapped and quantified. The hardware was then returned to service and later re-evaluated in the exact same locations after the additional operating time. INTRODUCTION This paper summarizes comprehensive corrosion studies carried out in seven industrial axial flow compressor installations. The operating experience of five FCC (refinery) main air blower applications and two lake side steel mill main air blower applications are the subject of this paper. Of interest, was the steel mill air quality and corrosion experiences were very similar to those measured in the refinery applications. The purpose of these studies was to determine what are the causes of flow path (rotor blades, stator vanes and rotor drum or disk) corrosion and when does the corrosion damage cause risk to the compressor reliability or significant performance deterioration. Additional goals of the evaluations were to determine if the noted corrosion in these compressors could be minimized or eliminated via metallurgical upgrades of the rotor. Long term reliable operation of the compressors is critical to successful process operation. All of the studied compressors were existing installations that were initially started between 1960 and 2003. In addition, all of the subject compressors had experienced at least a one rotor (blades and/or disc) failure in which rotor corrosion was either the cause or a major contributor to the failures. The basic methodology of the corrosion monitoring started by base-lining the condition of new hardware being installed into the compressors. Periodic assessment of the compressor hardware was then made via in-place crawl in inspection during unit shut downs, borescopic inspections during quick unit shut downs and unit disassembly at major turnarounds. In addition, several of the compressors were modified to accept online removable corrosion coupons.