Products & Services: Flange Sealing
Flange
Sealing
Air inleakage into steam turbines has far-reaching consequences
on plant efficiency and equipment life. An increase in condenser
back pressure can throttle unit efficiency and, in extreme cases,
cause low pressure turbine blade flutter.
High levels of dissolved O2 elevate corrosion in the feed water
heater train, boiler, and steam generator systems. Corrosion contributes
to poor heat transfer and threatens system integrity. High levels
of dissolved CO2 , balanced with ammonia to control pH, can increase
ionic concentrations in the condensing steam. Turbine disk cracking,
and other failure mechanisms result.
Hydrazene becomes an inefficient oxygen scavenger
at lower temperatures which makes air inleakage from the condenser
particularly troublesome.
Over time, the gasket between the waterbox and tubesheet can start
to breakdown due to embrittlement. Hydrodynamic stresses from waterbox
loading and possible startup water hammer further aggravate gasket
integrity. Differential thermal stresses resulting from steam dumps,
black trips, and the like compound the problem. Air inleakage around
the gasket, through the bolt holes, and into the condenser shell
is the result.
A variety of leak sealing methods have been employed resulting in
various degrees of success. Leak paths can be elusive with new ones
forming. Improperly applied sealing materials can delaminate. Often
additional sealing materials are applied over old repairs which can
result in an ineffective buildup of various paints, anti-sweat coatings,
caulks, and other compounds around the external condenser flange.
Plastocor,® Inc. has developed a methodology
whereby these old materials are completely removed and a new,
sealing system installed,
whereby air inleakage is completely eliminated from the waterbox-to-tubesheet
flange area. In addition, these methods can be applied to most
any other areas in the system where air intrudes.
For the external joint, these methods can be employed while the
unit is either on-line or off. The sealing system can be installed
as the previous materials are removed so severe leaks can be resealed
as they are uncovered. On-line applications should be done in conjunction
with leak detection surveillance.
The system is equally effective when applied on the inside of the
waterbox to stop cooling water inleakage or air inleakage in situations
where the waterboxes are not completely flooded.
