Thursday, June 25, 2020

Steam boiler water tube leakage

How to know
  • Excessive feed water consumption from cascade tank
  • Continuously running boiler feed pump
  • If large amount of leakage, boiler water level low, steam pressure drop & continuous firing of boiler
  • Some water comes out from furnace cover
  • White smoke escaping from boiler uptake
Check Leakage
For water tube boiler (Z boiler)
  • Stop firing and open combustion chamber, leakage can be seen easily.
  • For individually boiler water tube, fill up the boiler water level to full and check. If necessary, pressure test should be done.
For smoke tube boiler
  • Open the smoke side drain valve, water will come out if boiler tube is leaking.
  • After opened up the fireside cover and fill up the boiler water level until all smoke tubes are flooded, we can easily check which one is leaking ligaments.
Possible Sources of water leakage
  • Leakage from tubes
  • Distorted furnace crown plate.
  • Furnace shell plate, opposite to burner opening due to flame impingement.
  • Lower section plate of furnace, due to damage bricks works.
Possible causes of leakage
  • External wastage due to waterside corrosion and pitting caused by using bad quality feed water or improper boiler water treatment.
  • Wastage of the ligaments due to soot blowing with wet steam.
  • Due to local overheating or design fault, unequal thermal expansion between tube and tube plate
  • Due to overheating, deformation or panting tube plate
Remedy and temporary repair at sea(Ref: MIURA Z Boiler)
  • Confirm and identify the leaking water tube.
  • After confirmed, remove castable until its swaged section is exposed so that the stopper can be welded.
  • Cut off one side of the leaking tube by gas.
  • Insert stoppers upward and downward through the cut-off section and seal them all around by welding.
  • Fit anchors on the inside face of the water tube and apply castable .
  • follow the manufacturer's instructions.
This method is only for temporary damage control and the damaged water tube replaced as soon as possible 

Procedure for permanent repair in port
  • If happening in port and enough time and spares, repaired permanently by renewal of leaking tube with ship's crew or availabl e labor.
  • After cool down, inspection of leakage and opening up for renewal of tubes,
  • Cut both ends of leaking tube about 50 mm from tube plate and chisel out.
  • Remove remaining pieces by (i) chiseling and (ii) knocking out by heating and cooling to achieve shrinkage.
  • Clean polish tube holes for dye check for any cracks, minor damage at the tube hole.
  • Diametrical clearance between tube and hole about 1.5 mm.
  • The ends of new tube cleaned thoroughly and carefully expanded by rolling into the hole and tube plate.
  • New tube protruded from tube plate by 6 mm at least.
  • Bell mouthing should be 1 mm for every 25 mm of tube outside diameter plus 1.5 mm

1 comment:

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