Rebuilding of Stern Boss Flange
Due to bimetallic corrosion the Stern tube Boss Seal Surface has been damaged and required by Class
to be reconstructed / recovered. Traditional rewelding and on-site machining sems too time consuming and is associated with huge costs, and further delays in the docking schedule would be a fact.
Rebuilding a Stern Boss Flange
Location
Gemak Shipyard, Turkey
Job and report done by
Gemak Shipyard
PI-ES Marine AS
Wencon products used
Wencon Ceramic Cream, Wencon Ceramic Coatings & Wencon Release
Agent
Damage due to bimetallic corrosion
The Stern Tube Boss Seal Surface suffered damage due to bimetallic corrosion, necessitating reconstruction or recovery as mandated by Class regulations.
Traditional rewelding and on-site machining methods are both time-consuming and costly, posing a significant risk of further delays in the docking schedule.
The Class Surveyor has confirmed that the physical properties of the Stern Tube construction remain sufficient. Therefore, the primary task was straightforward: rebuilding the deteriorated metal.
The Wencon application process
Step 1: Rope guard removed
Oil drained and propeller dismantled.
Stern tube seal box and flange ring has been
protected with rubber gasket a plastic tape
before blasting. Stern boss corroded parts have been grit basted to SA 2½ / 75 mµ.
Step 2: Preparation
Seal box prepared and positioned on shaft.
Step 3: Release Agent
Wencnon release agent applied by brush to the flange ring surface and remain for about 20-25 min. Thereafter rubbed with clean clutch and
polished.
Step 4: Ceramic Cream
Wencon ceramic cream mixed in
accordance to instructions in the
box and applied to the corroded
parts of the boss.
Step 5: Flange ring bolted
Flange ring is bolted without gasket and
tightened firmly while the Wencon Ceramic
Cream was still wet.
Excess material is cleaned by scraper and left
for curing over the night.
Step 6: Flange ring dismantled
In the morning, which is about 16 hrs. of curing,
flange ring is dismantled. Excess material pop-up on the flange surface & the lubricating holes were recovered by hand to original shape and size. Those areas and the exit material around the flange edge were sanded flush by power disc and sandpaper.
Step 7: New gasket
Seal box has been put back with new gasket
and red silicone underneath. Bolts are
tightened in accordance with the required
torque.
Seal box refitted and Oil Filled and tested for
leaks.
Step 8: Protective coating
Wencon protective coating is applied
to the remaining corroded surface of
the stern boss from flange rings up to the
fwd. edge of the rope guard. The first coat is applied about 300 microns. Second coat is applied about 1 hr. of curing
with the same thickness. After 4 hrs. of curing, rope guard welded in place.
Step 9: Completed
The reconstruction process involves rebuilding the damaged metal surface, followed by the application of a double layer of protective coating. This approach ensures the lifetime extension of the Stern Tube, offering an efficient and cost-effective alternative to traditional methods.
