1. BOILER SIGHT GLASS FAILURE
CAER Presentation
March 27, 2014
Jim Riley
Acknowledgement: Bill Gamba, Joint Health and Safety Committee Co-Chair for investigation contributions

2. PRESENTATION OVERVIEW
Description of a 600# boiler sight glass failure
Damage mechanism associated with the failure
Progressive degradation over time of mica and glass
ITPM (inspection, testing, and preventive maintenance) tasks to prevent failures
Kicker box (if needed to summarize key point, otherwise delete)
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3. 600# Boiler sight glass failure
Split level gauge with two sight glasses/housings
Normal level in upper sight glass
Glass thinned to the point that it fractured and failed
Small steam release. No process materials were released. No unit upset occurred
Sight glass was isolated using chain wheels located at grade to close the block valves.
Redundant split level sight glasses at other end of the boiler and level float chamber/transmitter provided water level indication while this sight glass was serviced.
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4. Damage mechanisms
Alumina silicate high temperature glass is a silica lattice with alkali oxides as fluxing agents. It corrodes under two conditions:
Leaching (acid effect) where hydronium ions (H3O +) are exchanged for the alkalis in the glass
Etching (alkali effect) by hydroxyl ions (OH-) acting upon the anions Na+, K+, and B+++ followed by dissolution.
Ruby mica shields occur as monoclinic crystals which resist acids and alkalis. It degrades due to the layered pattern.
Condensing drops at the steam vapor/BFW level range
River patterns in the ruby mica layers attacked
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5. PROGRESSIVE DEGRADATION OF MICA/GLASS
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6. ITPM TASKS TO PREVENT FAILURES
Boiler operator surveillance specifically looking for ‘milky appearance’. Train operators on what to look for.
Redundant visual inspections by boiler permit inspectors at annual and 6-month external permit inspections.
Block in the sight glass if the ‘milky appearance’ due to etching/leaching of the glass becomes apparent. Do not leave the sight glass in service to further degrade.
Service the sight glass by replacing both the mica shields and the glass when they are ‘milky appearance’.
Service the sight glass by replacing both the mica shields and the glass when the internal boiler inspection is done based on permit variance period allowance.
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7. Any questions that you may have?
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