The scope of this paper is to discuss the background, design challenges, online damage assessment, repair selection and sustainment efforts undertaken to mitigate large scale caustic stress corrosion cracks in the common low pressure steam system. Caustic ingression in the steam system through contaminated boiler feed water used for de-superheating caused multiple cracks in the steam piping systems. Crack locations were predominantly visible at the longitudinal and circumferential weld joints of the common utilities steam header. Cracks were observed on the intrados and extrados of elbow joints, tee joints and straight pipe sections of the large size (52” and 48”) header. Cracks were also observed downstream of significant capacity de-super heaters and upstream of steam users in the process units. The common steam system is utilised for process heating, pump and compressor drivers. Unplanned shutdown of the common steam header system for repair or replacement would require a multiple mega train outage and majour business impact. Crack propagating beyond critical length will lead to catastrophic failure of the steam system. Online solutions needed to be (1) safe to install, (2) designed for sustainment for over 2 years until a permanent repair could be affected, and (3) not impose any risk of further damage during installation.


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