Inspection of Both Desuperheaters after Five Years of Service
Step 1: Superheater desuperheater
disassembly. The desuperheater installed
during the superheater inspection began with
removal of the actuator. Part of the main steam
lagging also was removed for proper access to
the lower nuts of the steam flange connection.
Courtesy: Tyco Flow Control
scratches showed up on the cylindrical part
of the spray cylinder, and visual inspection
led to the conclusion that these were most
likely mechanical fissures. A nondestructive
examination (NDE) test would confirm that
observation. Courtesy: Tyco Flow Control
Step 6: Reheat desuperheater disassembly. There was much more access to
the reheat desuperheater given the larger size
of its pipe—32-inch outer diameter (OD)—
than the superheat pipe (18-inch OD). The
liquid on the bolting is WD- 40 used as a rust
solvent. Courtesy: Tyco Flow Control
Step 4: NDE test. Next, a dye penetrant
NDE test was performed on the entire assembly. The investigation showed that zero
cracks or imperfections were present in the
spray cylinder, the flange area, and the nozzle area. Courtesy: Tyco Flow Control
Step 2: Remove for inspection.
Bolts from the steam flange were removed,
and the unit was raised from its stub connection. A visual inspection did not reveal any
cracks or imperfections. The flanged upper
part of the spray cylinder was in perfect condition as well as the sealing indication of the
RTJ groove. Courtesy: Tyco Flow Control
Step 5: Return to service. Plant management decided to reinstall the unit with no
further dismantling or testing. Plant records
showed excellent temperature control and
smooth responsiveness over the entire operating range since start-up, five years earlier. The
offset from setpoint was never more than 4C
on a controller over a 600C span. All operating and mechanical inspection results showed
that a complete overhaul was not required. The
desuperheater was then reinstalled and returned to service. Courtesy: Tyco Flow Control
Step 7: Remove for inspection. The
spray cylinder shows considerably more corrosion than the superheat unit because the unit
is fabricated from a ferritic steel that is prone
to oxidation. The superheat unit is constructed
from F91. Courtesy: Tyco Flow Control
Step 3: Visual inspection. The splash
pattern around the nozzles is typical of probe
type spray units. Because the plant was
standing idle for some days, oxidation of
the magnetite had occurred. Some small
Step 8: Visual inspection. The
flanged upper part also revealed no imperfections during visual inspection. Courtesy:
Tyco Flow Control
