Rudder Repair

A rudder of a vessel requires an extensive welding repairs and as a chief engineer you are requested to supervise.

Suggest a suitable type of welding process.

The welding process most suitable for rudder repair is MANUAL METAL ARC WELDING.

The reasons for using the basic process are:-

It will probably be in-situ repair in Dry-dock requiring multi-position welding (down hand, overhead, horizontal, vertical).

MMA is versatile in this respect.

There will be no special steel involved, thus basic electrodes techniques are to be used. (although coatings may be in rudder structure taken care by pre-heating.)

Welding in an exposed environment means the semi-automatic process such as MIG would be difficult(shielding gas blown away) unless protected by an enclosure.

State with reasons 4 common welding defects

Undercut - This is a groove or channel along the toe of the weld caused wastage of the parent metal which could be due to too high a welding current or low welding speed.

Inclusions- Any slag or other entrapped material is an inclusion defect. Surfaces to be welded must be free from foreign matter. 

E.g.:- grease oil, millscale, metal chipping etc. 

During welding the slag must not be allowed to get front of the molten metal or it may get entrapped.

Also when welding is interrupted, or another run is to be laid, the already deposited metal should be allowed to cool, slag should be chipped and brushed off.

Incomplete root penetration - It is a gap caused by failure of the weld metal to fill the root. This may due to fast welding speed or too low current.

Lack of Fusion- This would occur between weld metal and the parent metal, between different layers of weld metal or between contact surfaces of parent metal. It could be caused by incorrect current or voltage, dirt or grease etc. 

State what tests may be carried out before returning the rudder in service

Rudder should be hydraulically pressure tested upto 2.45 m of water head for confirming water-tight integrity from the top surface of rudder.

Welding work first should be tested by Non-Destructive Testing means X-rays, Ultrasonic testing. If it is satisfactory then hydraulic test should be carried out. 

Rudder drop to be checked to confirm load on the pintle bearings, condition of the pintle bearings, free movement of rudder 35 deg. on either side, external rudder stoppers before rudder is put back into service.

Proper fitment of sacrificial anodes. rudder closing plates and bottom drain to be checked for proper fitment. Rudder stock palm nuts to be covered with cementing.