16
6.2.
INTERNAL INSPECTION AND TUBE
PLUGGING
Hot fluid under pressure
Do not remove the piping or water covers until:
Ø
the system has been shut down (see section
5.3).
Ø
the box cooler has been isolated from the
system piping system, e.g. by closing the
service valves in the supply and return piping.
Ø
the box cooler and the attached piping are
cooled down to a safe temperature.
Ø
all pressure in the box cooler has been
relieved (slowly open the vent valve).
Ø
all liquid inside the system has been drained
Severe water leakage
The tube sheet to top plate connection is below
the waterline. Loosening the collar bolts/Allen
head screws of the tube bundle will result into
severe water leakage and is a breakdown of the
watertight integrity of the vessel.
DO NOT REMOVE THE TUBE BUNDLE OR THE
COLLAR BOLTS/ALLEN HEAD SCREWS WHEN THE
VESSEL IS AFLOAT!
Internal inspection and tube plugging can take place when
the ship is afloat, as long as the collar bolts/Allen head
screws remain secured.
1)
Remove the supply and return pipes
2)
Disassemble the water cover by loosening the bolts
and nuts of the water cover.
Do not loosen the collar bolts / Allen head screws!
3)
Carefully lift the water cover (see section 3.2).
Mind the weight. Take care not to damage the
coating nor the gasket faces of the flanges.
4)
Inspect the interior for fouling or signs of corrosion.
(It is not expected that internal cleaning of the tubes
will be necessary because the liquid should be
conditioned and circulates in a closed circuit.)
Flush each tube separately with a jet of water to check
if the tubes are clogged in the bends.
Clogged tubes or excessive fouling will reduce the heat
transfer and may contribute to internal corrosion of
the tubes, as deposits may retain corrosive elements.
When cleaning is required, refer to section 6.3.
Note that internal cleaning requires that the tube
bundle is dismounted from the top plate of the sea
chest. Therefore this can only be done during dry-‐
docking periods.
5)
Removal of the water cover also allows for the
identification of possible leaks in the tubes, as a leak
will cause seawater to seep into the tubes.
An emergency repair can be done by plugging both
ends of the damaged (leaking) tube.
Brass plugs can be obtained from Duramax Marine® or
they can be made from free-‐machining brass
(CuZn39Pb3). Alternatively, plugs can also be made
from wood. The use of other material may damage the
tube sheet.
Figure 15. Dimensions of tube plugs for the
CuZn20Al2 tubes Ø 11 x 0,8 mm.
6)
After inspection or repairs, install the water cover and
the piping according to the instructions of section
4.3.4 and 4.4.
Use new gaskets, do not reuse old gaskets.
7)
Re-‐commission and start the box cooler according the
instructions of sections 5.1 and 5.2
