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Bài gửi by shipdesign on Thu Aug 28, 2008 3:45 pm

Bowthruster Tunnel and Support Tube Corrosion


Inspection of a CP Tunnel thruster was carried out during a docking
period due to slight contamination of the gearbox oil by sea water. The
intention was to inspect with the head of oil still on the unit to see
if it was possible to ascertain if this was due to blade seal leakage,
or if it was necessary to remove the output shaft assembly
It was noted that of 8 anodes fitted in this space, 7 had no remaining anodic material. The final anode was severely depleted.


Anodes fitted to the output shaft flange were found absent

The ropeguard was damaged by corrosion and the effects of cavitation and turbulence


This excessive damage was attributed to lack of protection from the anodes exacerbated by cavitation and localised turbulence

The Support tube was pitted to a depth of 20 mm on the blade facing face.


Again this is attributed to corrosion damage exacerbated by localised turbulence.

This damage in particular was carefully examined to ensure that there were no structural strength or stress raiser issues
The adjacent areas to the blades on the tunnel were pitted and evidence of grooving either side of a circumferential weld.

Although this damage is typical of tunnel thrusters the degree in
comparison to age of the vessel and normal thrusters usage with regard
to zero pitch operation was deemed excessive Repairs

The areas were grit blasted to
allow further inspection. This revealed that there was sufficient depth
of material remaining to allow repairs to be carried out.
Shown is an area on the Tunnel adjacent to the blades after blasting and part coated with repair product




The selected method was build up using a two compound Metallic polymer product supplied by Belzona
After further cleaning and friable material removal Belzona 1111 was
applied to the damaged support tube and tunnel areas. An overlap of
around 50mm was given to ensure that any edge lifting would not affect
the main repair.
The initial application concentrated on ensuring full contact with the
base material by forcing small quantities of product into the pits
removing any air bubbles. The main layer was then built up on top of
this.

After a suitable cure period the areas were overcoated with a smooth
layer to reduce turbulence and improve the longevity of the repair.

The product used was Belzona 1341 applied by use of a brush to provide
a very smooth tenacious outer layer which also provides extra
protection against edge lifting.
Cleaning of tools was made possible by use of a release agent Belzona 9111Notes were made to specially inspect the damage at next docking. Were
edge lifting is evident it is possible to cut back the damaged areas
and overlay again with Belzona 1341.
The shaft seal landing face was machined to remove a grove formed by
rub of the two parts. The blade palms were inspected and no significant
damage noted. All seals were replaced and new anodes and ropeguard
fitted.

shipdesign
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Tổng số bài gửi : 174
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Đến từ: : shipdesign company
Nghề nghiệp/sở thióch : research
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Registration date : 24/05/2008

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