Liquid metal cracking is a form of environmental cracking
where molten metal penetrates the grain boundaries of the steel. Series 300
austenitic stainless steel tubes are particularly susceptible to this mechanism
from molten aluminum, zinc and cadmium. Fireboxes provide adequate temperatures
for these metals to be molten since they have relatively low melting points.
Contact of stainless steel surfaces with a low melting point metal should be
avoided during maintenance outages in particular; including incidental contact
such as using marking pens containing zinc and galvanized or aluminum
scaffolding poles rubbing against tubes.
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