Inspection and Repair of Deaerators

Transcription

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

Recommendations:
Spot RT/WFMP
Full Penetration welds
Post Weld Heat Treatment
(PWHT)
Blend Grinding

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Types of Deaerators
Limited to direct contact heaters rather

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than degasifiers
Spray vs. Tray
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Spray Type
Also known as spray scrubber
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
Also known as spray-tray
Uses cascading trays
Essentially 100% turn down
Protects vessel from non
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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
Capacities to 1,000,000#/hr
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

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
Annual Visual Inspection strongly
recommended
Heater and storage
Especially under and at steam inlet end
of the tray enclosure
Track results for year to year
comparison
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)
Most prevalent at steam inlet end
Also in proximity to any flashing returns
Especially just under the steam inlet
end of the tray box
UT any wasted areas and track results
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FAC
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FAC
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FAC
Most prevalent under tray enclosure
Near steam inlet
Around downcomer (vortex breakers?)
UT any wasted areas and track results
Thinning can happen VERY quickly
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
[email protected]
www.deaerator.com
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