Inspection and Repair of Deaerators

Inspection and Repair of
Deaerators
EPRI
Welding and Repair Technology for Power Plants
June 17, 2004
Presented by Paul Craven
Engineering Manager
Kansas City Deaerator Company
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Background
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KCD is a leading supplier of deaerators
worldwide.
Our service engineers have inspected
hundreds of deaerators over the last 30
years.
In 2003, EPRI commissioned KCD to write a
paper regarding the inspection and repair of
deaerators.
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NACE RP0590-96
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In response to catastrophic failures
NACE commissioned a study
Failures due to cracking around
the weld seams
30-40% of vessels inspected
required repair
WFMP testing to detect cracks
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NACE RP0590-96
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Recommendations:
Spot RT/WFMP
‹ Full Penetration welds
‹ Post Weld Heat Treatment
(PWHT)
‹ Blend Grinding
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Types of Deaerators
ƒ Limited to direct contact heaters rather
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than degasifiers
Spray vs. Tray
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Spray Type
ƒ Also known as spray scrubber
ƒ Used fixed orifice mixers rather than
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cascading trays
Limited turn down (20%)
Poor vessel protection
Somewhat uncommon in US utility plants
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Spray Unit Diagram
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Tray Type
ƒ Also known as spray-tray
ƒ Uses cascading trays
ƒ Essentially 100% turn down
ƒ Protects vessel from nonƒ
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condensables
Very typical in US plants
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Vertical Heater
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Vertical Heater
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Vertical Heater
ƒ Capacities to 1,000,000#/hr
ƒ Commonly used up to 700,000#hr
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Horizontal Heater
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Horizontal Heater
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Horizontal Heater
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Capacities to 16,000,000#/hr – so
far
De-facto standard for US utilities
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Sizing Basis
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Three variables affect sizing:
Throughput (over trays?)
‹ Temperature Rise
‹ Oxygen Content
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Changes in ANY of these impact
deaerator performance
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Performance Requirements
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Heat Water Inlet to Saturated Condition
Reduce Oxygen to 7 PPB (HEI Method)
Reduce Free CO2 to Zero (Alpha Method)
Operate Quietly For All Loads
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Typical Problems in
Vertical Units
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Typical Problems in
Vertical Units
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Typical Problems in
Horizontal Heaters
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Typical Problems in
Horizontal Heaters
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Vessel Inspection
ƒ Annual Visual Inspection strongly
recommended
ƒ Heater and storage
ƒ Especially under and at steam inlet end
of the tray enclosure
ƒ Track results for year to year
comparison
ƒ Special attention to the head to shell
seam
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Erosion (LIIE)
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Erosion (LIIE)
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Erosion (LIIE)
ƒ Most prevalent at steam inlet end
ƒ Also in proximity to any flashing returns
ƒ Especially just under the steam inlet
end of the tray box
ƒ UT any wasted areas and track results
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FAC
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FAC
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FAC
ƒ Most prevalent under tray enclosure
ƒ Near steam inlet
ƒ Around downcomer (vortex breakers?)
ƒ UT any wasted areas and track results
ƒ Thinning can happen VERY quickly
ƒ Over 1/8” in 6 months!
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Minimum Thickness
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Grind to sound metal (WFMP or
LDP to confirm)
UT for actual thickness
Check allowable internal/external
pressure
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De-Rate Vessel
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Interim solution to shell thinning
Check calculations
Reset safety valves
Consider re-stamping vessel
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Repair Methods
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Weld Overlay – small areas
Flush patches
Partial shell replacement
Full replacement
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Questions
Paul Craven
Engineering Manager
Kansas City Deaerator Company
913-338-2111
pcraven@deaerator.com
www.deaerator.com
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