Risk Analysis for Operation of Aluminum Heat Exchangers
Contaminated by Mercury
Wilhelm, S. M., "Risk Analysis for Operation of Aluminum Heat Exchangers
Contaminated by Mercury, Proceedings 4th Global Congress on Process Safety, 2008
AIChE Spring Meeting, New Orleans.
ABSTRACT
Brazed aluminum plate-fin heat exchangers are extensively used in gas
separation processes including LNG, LPG, NGL, nitrogen rejection and olefins
manufacture. In situations where mercury is a trace component of feed gas or
liquid feeds to crackers, condensation of liquid or precipitation of solid
mercury can occur in heat exchanger passes, even with functional mercury removal
systems in place. Mercury in liquid phase causes, under certain well-defined
conditions, liquid metal embrittlement of susceptible metallurgy or amalgam
corrosion of core fins, both of which can lead to sudden loss of pressure
containment. Mercury-contaminated aluminum heat exchangers require close
scrutiny and quantitative risk assessment to allow safe operation, remediation
or to justify replacement. The risk analysis procedure involves computational
prediction of mercury deposition, inspection of critical areas, detailed
assessment of metallurgy and fabrication, strain analysis of temperature changes
during trips and shutdowns and oxide fatigue analysis. Differentiation of leak
and rupture failure modes can be accomplished based on calculated amount of
deposition and on location of mercury deposits as determined from focused
inspection. Assigning probability of failure requires an intimate understanding
of the mechanistic influences to Liquid Metal Embrittlement (LME) crack
initiation and propagation. Failure statistics are essential to assignation of
probability-based risk factors.
Request a copy
Inspection Services
|
